View ADC10D020_973840.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

ADC10D020 Dual 10-Bit, 20 MSPS, 150 mW A/D Converter
September 2001
ADC10D020 Dual 10-Bit, 20 MSPS, 150 mW A/D Converter
General Description
The ADC10D020 is a dual low power, high performance CMOS analog-to-digital converter that digitizes signals to 10 bits resolution at sampling rates up to 30 MSPS while consuming a typical 150 mW from a single 3.0V supply. No missing codes is guaranteed over the full operating temperature range. The unique two stage architecture achieves 9.5 Effective Bits over the entire Nyquist band at 20 MHz sample rate. An output formatting choice of straight binary or 2's complement coding and a choice of two gain settings eases the interface to many systems. Also allowing great flexibility of use is a selectable 10-bit multiplexed or 20-bit parallel mode. An offset correction feature nulls the offset error to less than 1 LSB. To ease interfacing to most low voltage systems, the digital output power pins of the ADC10D020 can be tied to a separate supply voltage of 1.5V to 3.6V, making the outputs compatible with other low voltage systems. When not converting, power consumption can be reduced by pulling the PD (Power Down) pin high, placing the converter into a low power state where it typically consumes less than 1 mW and from which recovery is about 1 ms. Bringing the STBY (Standby) pin high places the converter into a standby mode where power consumption is about 27 mW and from which recovery is 800 ns. The ADC10D020's speed, resolution and single supply operation makes it well suited for a variety of applications, including high speed portable applications. Operating over the industrial (-40 TA +85C) temperature range, the ADC10D020 is available in a 48-pin TQFP. An evaluation board is available to ease the design effort.
Features
n n n n n n n n Internal sample-and-hold Dual gain settings Offset correction Selectable straight binary or 2's complement output Multiplexed or parallel output bus Single +2.7V to 3.6V operation Power down and standby modes 3V TTL Logic input/output compatible
Key Specifications
Resolution 10 Bits Conversion Rate 20 MSPS ENOB 9.5 Bits (typ) DNL 0.35 LSB (typ) Conversion Latency Parallel Outputs 2.5 Clock Cycles -- Multiplexed Outputs, I Data Bus 2.5 Clock Cycles -- Multiplexed Outputs, Q Data Bus 3 Clock Cycles n PSRR 50 dB n Power Consumption -- Normal Operation 150 mW (typ) -- Power Down Mode 1 mW (typ) -- Fast Recovery Standby Mode 27 mW (typ) n n n n n
Applications
n n n n n n Digital Video CCD Imaging Portable Instrumentation Communications Medical Imaging Ultrasound
(c) 2001 National Semiconductor Corporation
DS200255
www.national.com
Connection Diagram
20025501
TOP VIEW
Ordering Information
Industrial Temperature Range (-40C TA +85C) ADC10D020CIVS ADC10D020EVAL NS Package TQFP Evaluation Board
www.national.com
2
Block Diagram
20025502
3
www.national.com
Pin Descriptions and Equivalent Circuits
Pin No. 48 47 Symbol I+ I- Equivalent Circuit Description Analog inputs to "I" ADC. Nominal conversion range is 1.25V to 1.75V with GAIN pin low, or 1.0V to 2.0V with GAIN pin high. Analog inputs to "Q" ADC. Nominal conversion range is 1.25V to 1.75V with GAIN pin low, or 1.0V to 2.0V with GAIN pin high. Analog Reference Voltage input. The voltage at this pin should be in the range of 0.8V to 1.5V. With 1.0V at this pin and the GAIN pin low, the full scale differential inputs are 1 VP-P. With 1.0V at this pin and the GAIN pin high, the full scale differential inputs are 2 VP-P. This pin should be bypassed with a 1 F capacitor.
37 38
Q+ Q-
1
VREF
45
VCMO
This is an analog output which can be used to set the common mode voltage of the input. It should be bypassed with a minimum of 2 F low ESR capacitor in parallel with a 0.1 F capacitor. This pin has a nominal output voltage of 1.5V and has a 1 mA output capability.
Top of the reference ladder. Do not drive this pin. Bypass this pin with a 10 F low ESR capacitor and a 0.1 F capacitor. 43 VRP
Bottom of the reference ladder. Do not drive this pin. Bypass this pin with a 10 F low ESR capacitor and a 0.1 F capacitor. 44 VRN
www.national.com
4
Pin Descriptions and Equivalent Circuits
Pin No. 33 Symbol CLK Equivalent Circuit
(Continued) Description
Digital clock input for both converters. The analog inputs are sampled on the falling edge of this clock input. Output Bus Select. With this pin at a logic high, both the "I" and the "Q" data are present on their respective 10-bit output buses (Parallel mode of operation). When this pin is at a logic low, the "I" and "Q" data are multiplexed onto the "I" output bus and the "Q" output lines all remain at a logic low (multiplexed mode). Offset Correct pin. A low-to-high transition on this pin initiates an independent offset correction sequence for each converter, which takes 34 clock cycles to complete. During this time 32 conversions are taken and averaged. The result is subtracted from subsequent conversions. Each input pair should have 0V differential value during this entire 34 clock period. Output Format pin. When this pin is LOW the output format is Straight Binary. When this pin is HIGH the output format is 2's complement. This pin may be changed "on the fly", but this will result in errors for one or two conversions. Standby pin. The device operates normally with a logic low on this and the PD (Power Down) pin. With this pin at a logic high and the PD pin at a logic low, the device is in the standby mode where it consumes just 27 mW of power. It takes just 800 ns to come out of this mode after the STBY pin is brought low. Power Down pin that, when high, puts the converter into the Power Down mode where it consumes just 1 mW of power. It takes 1 ms to recover from this mode after the PD pin is brought low. If both the STBY and PD pins are low simultaneously, the PD pin dominates. This pin sets the internal signal gain at the inputs to the ADCs. With this pin low the full scale differential input peak-to-peak signal is equal to VREF. With this pin high the full scale differential input peak-to-peak signal is equal to 2 x VREF. 3V TTL/CMOS-compatible Digital Output pins that provide the conversion results of the I and Q inputs. I0 and Q0 are the LSBs, I9 and Q9 are the MSBs. Valid data is present just after the rising edge of the CLK input in the Parallel mode. In the multiplexed mode, valid data is present just after the rising edge of the CLK input for I0-I9 and just after the falling edge of the CLK input for Q0-Q9. Output data valid signal. In the multiplexed mode, this pin transitions from low to high when the data bus transitions from Q-data to I-data, and from high to low when the data bus transitions from I-data to Q-data. In the Parallel mode, this pin transitions from low to high as the output data changes. Positive analog supply pin. This pin should be connected to a quiet voltage source of +2.7V to +3.6V. VA and VD should have a common supply and be separately bypassed with 10 F to 50 F capacitors in parallel with 0.1 F capacitors.
2
OS
31
OC
32
OF
34
STBY
35
PD
36
GAIN
8 thru 27
I0-I9 and Q0-Q9
28
I/Q
40, 41
VA
5
www.national.com
Pin Descriptions and Equivalent Circuits
Pin No. Symbol Equivalent Circuit
(Continued) Description
4
VD
Positive digital supply pins. These pins should be connected to a quiet voltage source of +2.7V to +3.6V. VA and VD should have a common supply and be separately bypassed with 10 F to 50 F capacitors in parallel with 0.1 F capacitors. Positive digital output pins. These pins should be connected to a clean, quiet voltage source of +1.5V to VD and be bypassed with 10 F to 50 F capacitors in parallel with 0.1 F capacitors. These pins should also be well decoupled from VA and VD and never exceed VD. The ground return for the analog supply. AGND and DGND should be connected together close to the ADC10D020 package. The ground return for the digital supply. AGND and DGND should be connected together close to the ADC10D020 package. The ground return of the digital output drivers.
6, 30
DR VD
3, 39, 42, 46
AGND
5 7, 29
DGND DR GND
www.national.com
6
Absolute Maximum Ratings
2)
(Notes 1,
Operating Ratings (Notes 1, 2)
Operating Temperature Range VA, VD Supply Voltage DR VD Supply Voltage VIN Differential Voltage Range GAIN = Low GAIN = High VCM Input Common Mode Range GAIN = Low GAIN = High VREF Voltage Range Digital Input Pins Voltage Range VREF/4 to (VA-VREF/4) VREF/2 to (VA-VREF/2) 0.8V to 1.5V -0.3V to (VA +0.3V) VREF/2 VREF -40C TA +85C +2.7V to +3.6V +1.5V to VD
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Positive Supply Voltages Voltage on Any Pin Input Current at Any Pin (Note 3) Package Input Current (Note 3) Package Dissipation at TA = 25C ESD Susceptibility (Note 5) Human Body Model Machine Model Soldering Temperature, Infrared, 10 sec. (Note 6) Storage Temperature 2500V 250V 235C -65C to +150C 3.8V -0.3V to (VA or VD +0.3V)
25 mA 50 mA
See (Note 4)
Converter Electrical Characteristics
The following specifications apply for VA = +3.0 VDC, VD = +3.0 VDC, DR VD = +3.0 VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 3.0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50, trc = tfc = 2 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25C (Note 7). Symbol Parameter Conditions Typical (Note 8) Limits (Note 9) Units (Limits) LSB(max) LSB(max) LSB(min) Bits LSB(max) LSB(min) LSB(max) LSM(min) %FS(max) %FS(min) Bits 9.0 Bits(min) Bits Bits dB 56 dB(min) dB dB dB 56 dB(min) dB dB dB -62 dB(min) dB dB
STATIC CONVERTER CHARACTERISTICS INL DNL Integral Non-Linearity Differential Non-Linearity Resolution with No Missing Codes Without Offset Correction VOFF Offset Error With Offset Correction GE Gain Error +0.5 -4 -5
0.65 0.35
1.8
+1.2 -1.0 10 +10 -16 +2.0 -1.5 +6 -14
DYNAMIC CONVERTER CHARACTERISTICS fIN = 1.0 MHz, VIN = FSR -0.1 dB ENOB Effective Number of Bits fIN = 4.7 MHz, VIN = FSR -0.1 dB fIN = 9.5 MHz, VIN = FSR -0.1 dB fIN = 19.5 MHz, VIN = FSR -0.1 dB fIN = 1.0 MHz, VIN = FSR -0.1 dB SINAD Signal-to-Noise Plus Distortion Ratio fIN = 4.7 MHz, VIN = FSR -0.1 dB fIN = 9.5 MHz, VIN = FSR -0.1 dB fIN = 19.5 MHz, VIN = FSR -0.1 dB fIN = 1.0 MHz, VIN = FSR -0.1 dB SNR Signal-to-Noise Ratio fIN = 4.7 MHz, VIN = FSR -0.1 dB fIN = 9.5 MHz, VIN = FSR -0.1 dB fIN = 19.5 MHz, VIN = FSR -0.1 dB fIN = 1.0 MHz, VIN = FSR -0.1 dB THD Total Harmonic Distortion fIN = 4.7 MHz, VIN = FSR -0.1 dB fIN = 9.5 MHz, VIN = FSR -0.1 dB fIN = 19.5 MHz, VIN = FSR -0.1 dB 9.5 9.5 9.5 9.5 59 59 59 59 59 59 59 59 -73 -73 -73 -73
7
www.national.com
Converter Electrical Characteristics
(Continued) The following specifications apply for VA = +3.0 VDC, VD = +3.0 VDC, DR VD = +3.0 VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 3.0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50, trc = tfc = 2 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25C (Note 7). Parameter Conditions Typical (Note 8) -84 -92 -87 -87 -78 -80 -80 -78 76 75 75 74 60 1023 0 140 1 MHz input to tested channel, 4.75 MHz input to other channel fIN = 8 MHz MHz Limits (Note 9) Units (Limits) dB dB dB dB dB dB dB dB dB dB dB dB dB
Symbol
DYNAMIC CONVERTER CHARACTERISTICS fIN = 1.0 MHz, VIN = FSR -0.1 dB HS2 Second Harmonic fIN = 4.7 MHz, VIN = FSR -0.1 dB fIN = 9.5 MHz, VIN = FSR -0.1 dB fIN = 19.5 MHz, VIN = FSR -0.1 dB fIN = 1.0 MHz, VIN = FSR -0.1 dB HS3 Third Harmonic fIN = 4.7 MHz, VIN = FSR -0.1 dB fIN = 9.5 MHz, VIN = FSR -0.1 dB fIN = 19.5 MHz, VIN = FSR -0.1 dB fIN = 1.0 MHz, VIN = FSR -0.1 dB SFDR Spurious Free Dynamic Range fIN = 4.7 MHz, VIN = FSR -0.1 dB fIN = 9.5 MHz, VIN = FSR -0.1 dB fIN = 19.5 MHz, VIN = FSR -0.1 dB IMD Intermodulation Distortion Overrange Output Code Underrange Output Code FPBW Full Power Bandwidth INTER-CHANNEL CHARACTERISTICS Channel - Channel Isolation Channel - Channel Aperture Delay Match Channel - Channel Gain Matching REFERENCE AND ANALOG CHARACTERISTICS VIN CIN RIN VREF IREF VCMO TC VCMO VIH VIL IIH IIL Analog Differential Input Range Analog Input Capacitance (each input) Analog Differential Input Resistance Reference Voltage Reference Input Current Common Mode Voltage Output Common Mode Voltage Temperature Coefficient Logical "1" Input Voltage Logical "0" Input Voltage Logical "1" Input Current Logical "0" Input Current VA = +2.7V VA = +3.6V VIH = VA VIL = DGND 1 -1 DR VD -0.3V 0.4 1 mA load to ground (sourcing current) Gain Pin = AGND Gain Pin = VA Clock High Clock Low 1 2 5 3 90 1.0 1 1.5 20 1.35 1.6 0.8 1.5 VP-P VP-P pF pF k V(min) V(max) A V(min) V(max) ppm/C 90 8.5 0.03 dB ps %FS fIN1 < 4.0 MHz, VIN = FSR -6.1 dB fIN2 < 6.0 MHz, VIN = FSR -6.1 dB (VIN+-VIN-) > 1.1V (VIN+-VIN-) < -1.1V
DIGITAL INPUT CHARACTERISTICS 2.0 0.5 V(min) V(max) A A
DIGITAL OUTPUT CHARACTERISTICS VOH VOL Logical "1" Output Voltage Logical "0" Output Voltage DR VD = +2.7V, IOUT = -0.5 mA DR VD = +2.7V, IOUT = 1.6 mA
8
V(min) V(max)
www.national.com
Converter Electrical Characteristics
(Continued) The following specifications apply for VA = +3.0 VDC, VD = +3.0 VDC, DR VD = +3.0 VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 3.0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50, trc = tfc = 2 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25C (Note 7). Parameter Conditions Typical (Note 8) -7 -14 7 14 47.6 8.8 0.22 1.3 0.1 0.1 150 178 27 1 90 52 169 1.4 55 Limits (Note 9) Units (Limits) mA mA mA mA mA(max) mA mA mA(max) mA mA mW(max) mW mW mW dB dB
Symbol
DIGITAL OUTPUT CHARACTERISTICS +ISC -ISC Output Short Circuit Source Current Output Short Circuit Sink Current VOUT = 0V VOUT = DR VD Parallel Mode Multiplexed Mode Parallel Mode Multiplexed Mode
POWER SUPPLY CHARACTERISTICS PD = LOW, STBY = LOW, dc input IA + ID Core Supply Current PD = LOW, STBY = HIGH PD = HIGH, STBY = LOW or HIGH DR ID Digital Output Driver Supply Current (Note 10) PD = LOW, STBY = LOW, dc input PD = LOW, STBY = HIGH PD = HIGH, STBY = LOW or HIGH PD = LOW, STBY = LOW, dc input PWR Power Consumption PD = LOW, STBY = LOW, 1 MHz Input PD = LOW, STBY = HIGH PD = HIGH, STBY = LOW or HIGH PSRR1 Power Supply Rejection Ratio PSRR2 Power Supply Rejection Ratio Change in Full Scale with 2.7V to 3.6V Supply Change Rejection at output of 20 MHz, 250 mVP-P Riding on VA and VD
AC Electrical Characteristics
OS = Low (Multiplexed Mode)
The following specifications apply for VA = +3.0 VDC, VD = +3.0 VDC, DR VD = +3.0VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50, trc = tfc = 2 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25C (Note 7) Symbol fCLK1 fCLK2 Parameter Maximum Clock Frequency Minimum Clock Frequency Duty Cycle Pipeline Delay (Latency) I Data Q Data tr, tf tOC tOD tDIQ tDIQD tAD tAJ tVALID Output Rise and Fall Times Offset Correction Pulse Width Output Delay from CLK Edge to Data Valid I/O Output Delay I/Q to Data Delay Sampling (Aperture) Delay Aperture Jitter Data Valid Time Overrange Recovery Time tWUPD PD Low to 1/2 LSB Accurate Conversion (Wake-Up Time) Differential VIN step from 1.5V to 0V Load on I/Q pin = 30 pF 13 17 3 1 4 10 18 2.5 3.0 Clock Cycles Clock Cycles ns ns(min) ns(max) ns ns ns ps(rms) ns ns s Conditions Typical (Note 8) 30 1 50 30 70 Limits (Note 9) 20 Units (Limits) MHz(min) MHz %(min) %(max)
< 10
4.5 50 4
9
www.national.com
AC Electrical Characteristics
OS = Low (Multiplexed Mode) (Continued) The following specifications apply for VA = +3.0 VDC, VD = +3.0 VDC, DR VD = +3.0VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50, trc = tfc = 2 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25C (Note 7)
Parameter STBY Low to 1/2 LSB Accurate Conversion (Wake-Up Time) Conditions Typical (Note 8) 450 Limits (Note 9) Units (Limits) ns
Symbol tWUSB
AC Electrical Characteristics
OS = High (Parallel Mode)
The following specifications apply for VA = +3.0 VDC, VD = +3.0 VDC, DR VD = +3.0VDC, VREF = 1.0 VDC, GAIN = OF = 0V, OS = 3.0V, VIN (ac coupled) = FSR = 1.0 VP-P, CL = 15 pF, fCLK = 20 MHz, 50% Duty Cycle, RS = 50, trc = tfc = 2 ns, NOT offset corrected. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25C (Note 7) Symbol fCLK1 fCLK2 Parameter Maximum Clock Frequency Minimum Clock Frequency Duty Cycle Pipeline Delay (Latency) tr, tf toc tOD tDIQ tDIQD tAD tAJ tVALID Output Rise and Fall Times OC Pulse Width Output Delay from CLK Edge to Data Valid I/O Output Delay I/Q to Data Delay Sampling (Aperture) Delay Aperture Jitter Data Valid Time Overrange Recovery Time tWUPD tWUSB PD Low to 1/2 LSB Accurate Conversion (Wake-Up Time) STBY Low to 1/2 LSB Accurate Conversion (Wake-Up Time) Differential VIN step from 1.5V to 0V Load on I/Q pin = 30 pF 15 16 1 1 7 10 21 Conditions Typical (Note 8) 30 1 50 30 70 2.5 Limits (Note 9) 20 Units (Limits) MHz(min) MHz %(min) %(max) Conv Cycles ns ns ns(max) ns ns ns ps(rms) ns ns s ns
< 10
11 50 4 450
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 2: All voltages are measured with respect to GND = AGND = DGND = 0V, unless otherwise specified. Note 3: When the input voltage at any pin exceeds the power supplies (VIN < GND or VIN > VA or VD), the current at that pin should be limited to 25 mA. The 50 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 25 mA to two. Note 4: The absolute maximum junction temperature (TJmax) for this device is 150C. The maximum allowable power dissipation is dictated by TJmax, the junction-to-ambient thermal resistance (JA), and the ambient temperature (TA), and can be calculated using the formula PDMAX = (TJmax - TA )/JA. In the 48-pin TQFP, JA is 76C/W, so PDMAX = 1,645 mW at 25C and 855 mW at the maximum operating ambient temperature of 85C. Note that the power dissipation of this device under normal operation will typically be about 170 mW (150 mW quiescent power + 20 mW due to 1 LVTTL load on each digital output). The values for maximum power dissipation listed above will be reached only when the ADC10D020 is operated in a severe fault condition (e.g. when input or output pins are driven beyond the power supply voltages, or the power supply polarity is reversed). Obviously, such conditions should always be avoided. Note 5: Human body model is 100 pF capacitor discharged through a 1.5 k resistor. Machine model is 220 pF discharged through 0. Note 6: See AN450, "Surface Mounting Methods and Their Effect on Product Reliability", or the section entitled "Surface Mount" found in any post 1986 National Semiconductor Linear Data Book, for other methods of soldering surface mount devices. Note 7: The inputs are protected as shown below. Input voltage magnitude up to 300 mV beyond the supply rails will not damage this device. However, errors in the A/D conversion can occur if the input goes beyond the limits given in these tables.
www.national.com
10
AC Electrical Characteristics
OS = High (Parallel Mode)
(Continued)
20025506
Note 8: Typical figures are at TJ = 25C, and represent most likely parametric norms. Note 9: Test limits are guaranteed to National's AOQL (Average Outgoing Quality Level). Performance is guaranteed only at VREF = 1.0V and a clock duty cycle of 50%. The limits for VREF and clock duty cycle specify the range over which reasonable performance is expected. Note 10: DR ID is the current consumed by the switching of the output drivers and is primarily determined by the load capacitance on the output pins, the supply voltage, DR VD, and the rate at which the outputs are switching (which is signal dependent). DR ID = DR VD (CO x fO + C1 x f1 + ... + C11 x f11) where DR VD is the output driver power supply voltage, Cn is the total capacitance on the output pin, and fn is the average frequency at which that pin is toggling.
Timing Diagrams
20025507
ADC10D020 Timing Diagram for Parallel Mode
11
www.national.com
Timing Diagrams
(Continued)
20025508
ADC10D020 Timing Diagram for Multiplexed Mode
20025509
FIGURE 1. AC Test Circuit
www.national.com
12
Specification Definitions
APERTURE (SAMPLING) DELAY is that time required after the fall of the clock input for the sampling switch to open. The Sample/Hold circuit effectively stops capturing the input signal and goes into the "hold" mode tAD after the clock goes low. APERTURE JITTER is the variation in aperture delay from sample to sample. Aperture jitter shows up as input noise. CLOCK DUTY CYCLE is the ratio of the time that the clock waveform is high to the total time of one clock period. CROSSTALK is coupling of energy from one channel into the other channel. DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1 LSB. Measured at 20 MSPS with a ramp input. EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE BITS) is another method of specifying Signal-to-Noise and Distortion Ratio, or SINAD. ENOB is defined as (SINAD - 1.76)/6.02 and says that the converter is equivalent to a perfect ADC of this (ENOB) number of bits. FULL POWER BANDWIDTH (FPBW) is the frequency at which the reconstructed output fundamental drops 3 dB below its 1 MHz value for a full scale input. GAIN ERROR is the difference between the ideal and actual differences between the input levels at which the first and last code transitions occur. That is, how far this difference is from Full Scale. INTEGRAL NON LINEARITY (INL) is a measure of the maximum deviation of each individual code from a line drawn from zero scale (12 LSB below the first code transition) through positive full scale (12 LSB above the last code transition). The deviation of any given code from this straight line is measured from the center of that code value. The end point test method is used. Measured at 20 MSPS with a ramp input. INTERMODULATION DISTORTION (IMD) is the creation of spectral components that are not present in the input as a result of two sinusoidal frequencies being applied to the ADC input at the same time. It is defined as the ratio of the power in the first and second order intermodulation products to the total power in one of the original frequencies. IMD is usually expressed in dB. LSB (LEAST SIGNIFICANT BIT) is the bit that has the smallest value of weight of all bits. This value is m * VREF/2n where "m" is the reference scale factor and "n" is the ADC resolution, which is 10 in the case of the ADC10D020. The value of "m" is determined by the logic level at the gain pin and has a value of 1 when the gain pin is at a logic low and a value of 2 when the gain pin is at a logic high.
MISSING CODES are those output codes that are skipped or will never appear at the ADC outputs. These codes cannot be reached with any input value. MSB (MOST SIGNIFICANT BIT) is the bit that has the largest value or weight. Its value is one half of full scale. OFFSET ERROR is a measure of how far the mid-scale transition point is from the ideal zero voltage input. OUTPUT DELAY is the time delay after the rising edge of the input clock before the data update is present at the output pins. OVERRANGE RECOVERY TIME is the time required after the differential input voltages goes from 1.5V to 0V for the converter to recover and make a conversion with its rated accuracy. PIPELINE DELAY (LATENCY) is the number of clock cycles between initiation of conversion and when that data is presented to the output driver stage. New data is available at every clock cycle, but the data output lags the input by the Pipelined Delay plus the Output Delay. POWER SUPPLY REJECTION RATIO (PSRR) can be one of two specifications. PSRR1 (DC PSRR) is the ratio of the change in full scale gain error that results from a power supply voltage change from 2.7V to 3.6V. PSRR2 (AC PSRR) is measured with a 20 MHz, 250 mVP-P signal riding upon the power supply and is the ratio of the output amplitude of that signal at the output to its amplitude on the power supply pin. PSRR is expressed in dB. SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in dB, of the rms value of the input signal at the output to the rms value of the sum of all other spectral components below one-half the sampling frequency, not including harmonics or dc. SIGNAL TO NOISE PLUS DISTORTION (S/(N+D) or SINAD) is the ratio, expressed in dB, of the rms value of the input signal at the output to the rms value of all of the other spectral components below half the clock frequency, including harmonics but excluding dc. SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the rms values of the input signal at the output and the peak spurious signal, where a spurious signal is any signal present in the output spectrum that is not present at the input. TOTAL HARMONIC DISTORTION (THD) is the ratio, expressed in dB, of the rms total of the first six harmonic components to the rms value of the input signal at the output.
13
www.national.com
Typical Performance Characteristics
specified Typical INL
VA = VD = DR VD = 3.0V, fCLK = 20 MHz, unless otherwise INL vs. Supply Voltage
20025511
20025512
INL vs. VREF
INL vs. fCLK
20025513
20025514
INL vs. Clock Duty Cycle
INL vs. Temperature
20025515
20025516
www.national.com
14
Typical Performance Characteristics
specified (Continued) Typical DNL
VA = VD = DR VD = 3.0V, fCLK = 20 MHz, unless otherwise
DNL vs. Supply Voltage
20025517
20025518
DNL vs. VREF
DNL vs. fCLK
20025519
20025520
DNL vs. Clock Duty Cycle
DNL vs. Temperature
20025521
20025522
15
www.national.com
Typical Performance Characteristics
specified (Continued) SNR vs. Supply Voltage
@ fIN = 1 MHz to 9.5 MHz
VA = VD = DR VD = 3.0V, fCLK = 20 MHz, unless otherwise
SNR vs. VREF
@ fIN = 4.7 MHz
20025523
20025524
SNR vs. fCLK
@ fIN = 9.5 MHz
SNR vs. fIN
20025525
20025526
SNR vs. Clock Duty Cycle @ fIN = 4.7 MHz
SNR vs. VDR @ fIIN = 4.7 MHz, fQIN = 9.5 MHz
20025527
20025528
www.national.com
16
Typical Performance Characteristics
specified (Continued) SNR vs. VCM @ fIIN = 4.7 MHz, fQIN = 9.5 MHz
VA = VD = DR VD = 3.0V, fCLK = 20 MHz, unless otherwise
SNR vs. Temperature @ fIN = 1 MHz to 9.5 MHz
20025529
20025530
SINAD & ENOB vs. Supply Voltage @ fIN = 1 MHz to 9.5 MHz
SINAD & ENOB vs. VREF @ fIN = 4.7 MHz
20025531
20025532
SINAD & ENOB vs. @ fCLK (fIN = 9.5 MHz)
SINAD & ENOB vs. fIN
20025533
20025534
17
www.national.com
Typical Performance Characteristics
specified (Continued)
VA = VD = DR VD = 3.0V, fCLK = 20 MHz, unless otherwise
SINAD & ENOB vs. Clock Duty Cycle @ fIN = 4.7 MHz
SINAD & ENOB vs. DR VD @ fIIN = 4.7 MHz, fQIN = 9.5 MHz
20025535
20025536
SINAD & ENOB vs. Temperature @ fIN = 1 MHz to SINAD & ENOB vs. VCM @ fIIN = 4.7 MHz, fQIN = 9.5 MHz 9.5 MHz
20025537
20025538
Distortion vs. Supply Voltage @ fIN = 4.7 MHz
Distortion vs. VREF @ fIN = 4.7 MHz
20025539
20025540
www.national.com
18
Typical Performance Characteristics
specified (Continued) Distortion vs. fCLK @ fIN = 9.5 MHz
VA = VD = DR VD = 3.0V, fCLK = 20 MHz, unless otherwise
Distortion vs. fIN
20025541
20025542
Distortion vs. Clock Duty Cycle @ fIN = 4.7 MHz
Distortion vs. DR VD @ fIIN = 4.7 MHz, fQIN = 9.5 MHz
20025543
20025544
Distortion vs. VCM @ fIIN = 4.7 MHz, fQIN = 9.5 MHz
Distortion vs. Temperature
20025545
20025546
19
www.national.com
Typical Performance Characteristics
specified (Continued) SFDR vs. Supply Voltage @ fIN = 4.7 MHz
VA = VD = DR VD = 3.0V, fCLK = 20 MHz, unless otherwise
SFDR vs. VREF @ fIN = 4.7 MHz
20025547
20025548
SFDR vs. fCLK @ fIN = 9.5 MHz
SFDR vs. fIN
20025549
20025550
SFDR vs. Clock Duty Cycle @ fIN = 4.7 MHz
SFDR vs. DR VD @ fIIN = 4.7 MHz, fQIN = 9.5 MHz
20025551
20025552
www.national.com
20
Typical Performance Characteristics
specified (Continued) SFDR vs. VCM @ fIIN = 4.7 MHz, fQIN = 9.5 MHz
VA = VD = DR VD = 3.0V, fCLK = 20 MHz, unless otherwise
SFDR vs. Temperature @ fIIN = 4.7 MHz
20025553
20025554
Crosstalk vs. fIN
Crosstalk vs. VDR @ fIIN = 4.7 MHz, fQIN = 9.5 MHz
20025555
20025556
Crosstalk vs. VCM @ fIIN = 4.7 MHz, fQIN = 9.5 MHz
Crosstalk vs. Temperature
20025557
20025558
21
www.national.com
Typical Performance Characteristics
specified (Continued) Power Consumption vs. Supply Voltage
VA = VD = DR VD = 3.0V, fCLK = 20 MHz, unless otherwise
Power Consumption vs. fCLK
20025559
20025560
Power Consumption vs. Temperature
Spectral Response @ fIN = 1 MHz
20025561
20025562
Spectral Response @ fIN = 4.7 MHz
Spectral Response @ fIN = 9.5 MHz
20025563
20025564
www.national.com
22
Typical Performance Characteristics
specified (Continued) Spectral Response @ fIN = 21 MHz
VA = VD = DR VD = 3.0V, fCLK = 20 MHz, unless otherwise
Spectral Response @ fIN = 49 MHz
20025565
20025566
Spectral Response @ fIN = 99 MHz
IMD Response @ fIN = 4.9 MHz, 5.1 MHz
20025581
20025568
Functional Description
The ADC10D020 uses an internal sample-and-hold amplifier (SHA) to enable sustained dynamic performance for signals of input frequency beyond the clock rate. This SHA also lowers the converter's input capacitance and reduces the number of external components required. Using a subranging architecture, the ADC10D020 achieves 9.5 effective bits over the entire Nyquist band at 20 MSPS while consuming just 150 mW. The use of an internal sample-and-hold amplifier (SHA) not only enables this sustained dynamic performance, but also lowers the converter's input capacitance and reduces the number of external components required. Analog signals at the "I" and "Q" inputs that are within the voltage range set by VREF and the GAIN pin are digitized to ten bits at up to 30 MSPS. VREF has a range of 0.8V to 1.5V, providing a differential peak-to-peak input range of 0.8 VP-P to 1.5 VP-P with the GAIN pin at a logic low, or an input range of 1.6 VP-P to 3.0 VP-P with the GAIN pin at a logic high. Differential input voltages less than -VREF/2 with the GAIN pin low, or less than -VREF with the GAIN pin high will cause the output word to indicate a negative full scale. Differential input voltages greater than VREF/2 with the GAIN pin low, or greater than VREF with the GAIN pin high, will cause the output word to indicate a positive full scale.
Both "I" and "Q" channels are sampled simultaneously on the falling edge of the clock input, while the timing of the data output depends upon the mode of operation. In the parallel mode, the "I" and "Q" output busses contain the conversion result for their respective inputs. The "I" and "Q" channel data are present and valid at the data output pins tOD after the rising edge of the input clock. In the multiplexed mode, "I" channel data is available at the digital outputs tOD after the rise of the clock edge, while the "Q" channel data is available at the digital outputs tOD after the fall of the clock. Data latency in the parallel mode is 2.5 clock cycles. In the multiplexed mode data latency is 2.5 clock cycles for the "I" channel and 3.0 clock cycles for the "Q" channel. The ADC10D020 will convert as long as the clock signal is present and the PD and STBY pins are low. Throughout this discussion,VCM refers to the Common Mode input voltage of the ADC10D020 while VCMO refers to its Common Mode output voltage.
Applications Information
1.0 THE ANALOG INPUTS Each of the analog inputs of the ADC10D020 consists of a switch (transmission gate) followed by a switched capacitor amplifier. The capacitance seen at each input pin changes
23 www.national.com
Applications Information
(Continued)
with the clock level, appearing as about 3 pF when the clock is low, and about 5 pF when the clock is high. A switched capacitance is harder to drive that is a larger, fixed capacitance. The CLC409 and the CLC428 dual op amp have been found to be a good amplifiers to drive the ADC10D020 because of their wide bandwidth and low distortion. They also have good Differential Gain and Differential Phase performance. Care should be taken to avoid driving the input beyond the supply rails, even momentarily, as during power-up. The ADC10D020 is designed for differential input signals for best performance. With a 1.0V reference and the GAIN pin at a logic low, differential input signals up to 1.0 VP-P are digitized. See Figure 2. For differential signals, the input common mode is expected to be about 1.5V, but the inputs are not sensitive to the common-mode voltage and can be anywhere within the supply rails (ground to VA) with little or no performance degradation, as long as the signal swing at the individual input pins is no more than 300 mV beyond the supply rails. For single ended drive, operate the ADC10D020 with the GAIN pin at a logic low, connect one pin of the input pair to 1.5V (VCM) and drive the other pin of the input pair with 1.0 VP-P centered around 1.5V. Because of the larger signal swing at one input for single-ended operation, distortion performance will not be as good as with a differential input signal. Alternatively, single-ended to differential conversion with a transformer provides a quick, easy solution for those applications not requiring response to dc and low frequencies. See Figure 3. The 330 resistors and 10 pF capacitor values are chosen to provide a cutoff frequency near the clock frequency to compensate for the effects of input sampling. 2.0 REFERENCE INPUTS The VRP and VRN pins should each be bypassed with a 5 F (or larger) tantalum or electrolytic capacitor and a 0.1 F ceramic capacitor. Use these pins only for bypassing. DO NOT connect anything else to these pins.
variability. The reference voltage at the VREF pin should be bypassed to AGND with a 5 F (or larger) tantalum or electrolytic capacitor and a 0.1 F ceramic capacitor. The circuit of Figure 6 may be used if it is desired to obtain a precise reference voltage not available with a fixed reference. The 240 and 1k resistors can be replaced with a potentiometer, if desired.
20025569
FIGURE 2. The ADC10D020 is designed for use with differential signals of 1.0 VP-P with a common mode voltage of 1.5V. The signal swing should not cause any pin to experience a swing more than 300 mV beyond the supply rails.
Figure 4 shows a simple reference biasing scheme with minimal components. While this circuit will suffice for many applications, the value of the reference voltage will depend upon the supply voltage.
The circuit of Figure 5 is an improvement over the circuit of Figure 4 because the reference voltage is independent of supply voltage. This reduces problems of reference voltage
20025570
FIGURE 3. Use of an input transformer for single-ended to differential conversion can simplify circuit design for single-ended signals.
www.national.com
24
Applications Information
(Continued)
20025571
FIGURE 4. Simple Reference Biasing
25
www.national.com
Applications Information
(Continued)
20025572
FIGURE 5. Improved Low Component Count Reference Biasing The VCMO output can be used as the ADC reference source as long as care is taken to prevent excessive loading of this pin. Since the reference input of the ADC10D020 is buffered, there is virtually no loading on the VCMO output by the VREF pin. While the ADC10D040 will work with a 1.5V reference voltage, it is fully specified for a 1.0V reference. To use the VCMO for a reference voltage at 1.0V, the 1.5V VCMO output may need to be divided down. The divider resistor values need to be carefully chosen to prevent excessive VCMO loading. See Figure 7. While the average temperature coefficient of VCMO is 20 ppm/C, that temperature coefficient can be broken down to a typical 50 ppm/C between -40C and +25C and a typical -12 ppm/C between +25C and +85C.
www.national.com
26
Applications Information
(Continued)
20025573
FIGURE 6. Setting An Accurate Reference Voltage
27
www.national.com
Applications Information
(Continued)
20025574
FIGURE 7. The VCMO output pin may be used as an internal reference source if its output is divided down and not loaded excessively. 2.1 REFERENCE VOLTAGE The reference voltage should be within the range specified in the Operating Ratings table (0.8V to 1.5V). A reference voltage that is too low could result in a noise performance that is less than desired because the quantization level falls below other noise sources. On the other hand, a reference voltage that is too high means that an input signal that produces a full scale output uses such a large input range that the input stage is less linear, resulting in a degradation of distortion performance. Also, for large reference voltages, the internal ladder buffer runs out of head-room, leading to a reduction of gain in that buffer and causing gain error. The Reference bypass pins VRP and VRN are output compensated and should each be bypassed with a parallel combination of a 5 F (minimum) and 0.1 F capacitors. As mentioned in the previous section, the VCMO output can be used as the ADC reference. 2.2 VCMO OUTPUT The VCMO output pin is intended to provide a common mode bias for the differential input pins of the ADC10D020. It can also be used as a voltage reference source. Care should be taken, however, to avoid loading this pin with more than 1 mA. A load greater than this could result in degraded long term and temperature stability of this voltage. The VCMO pin is output compensated and should be bypassed with a 2 F/0.1 F combination, minimum. See 2.0 REFERENCE INPUTS for more information on using the VCMO output as a reference source. 3.0 DIGITAL INPUT PINS The seven digital input pins are used to control the function of the ADC10D020.
www.national.com
28
Applications Information
3.1 CLOCK (CLK) INPUT
(Continued)
voltages do not have to be equal to each other. Because of the uncertainty as to exactly when the conversion sequence starts, it is best to allow 35 clock periods for this sequence. 3.4 OUTPUT FORMAT (OF) PIN The Output Format (OF) pin provides a choice of straight binary or 2's complement output formatting. With this pin at a logic low, the output format is straight binary. With this pin at a logic high, the output format is 2's complement. 3.5 STANDBY (STBY) PIN The Standby (STBY) pin may be used to put the ADC10D020 into a low power mode where it consumes just 27 mW and can quickly be brought to full operation. The device operates normally with a logic low on this and the PD pins. 3.6 POWER DOWN (PD) PIN The Power Down (PD) pin puts the device into a low-power "sleep" state where it consumes just 1 mW when at a logic high. Power consumption is reduced more when the PD pin is high than when the STBY pin is high, but recovery to full operation is much quicker from the standby state than it is from the power down state. When the STBY and PD pins are both high, the ADC10D020 is in the power down mode. 3.7 GAIN PIN The GAIN pin sets the internal signal gain of the "I" and "Q" inputs. With this pin at a logic low, the full scale differential peak-to-peak input signal is equal to VREF. With the GAIN pin at a logic high, the full scale differential peak-to-peak input signal is equal to 2 times VREF. 4.0 INPUT/OUTPUT RELATIONSHIP ALTERNATIVES The GAIN pin of the ADC10D020 offers input range selection, while the OF pin offers a choice of straight binary or 2's complement output formatting. The relationship between the GAIN, OF, analog inputs and the output code are as defined in Table 1. Keep in mind that the input signals must not exceed the power supply rails.
The clock (CLK) input is common to both A/D converters. This pin is CMOS/LVTTL compatible with a threshold of about VA/2. Although the ADC10D020 is tested and its performance is guaranteed with a 20 MHz clock, it typically will function well with low-jitter clock frequencies from 1 MHz to 30 MHz. The clock source should be series terminated and the ADC clock pin should be shunt terminated with a 100 resistor in series with a capacitor whose impedance is 60 to 90 at the fundamental of the clock frequency. The rise and fall times of the clock supplied to the ADC clock pin should be no more than 2 ns. The analog inputs I = (I+) - (I-) and Q = (Q+) - (Q-) are simultaneously sampled on the falling edge of this input to ensure the best possible aperture delay match between the two channels. 3.2 OUTPUT BUS SELECT (OS) PIN The Output Bus Select (OS) pin determines whether the ADC10D020 is in the parallel or multiplexed mode of operation. A logic high at this pin puts the device into the parallel mode of operation where "I" and "Q" data appear at their respective output buses. A logic low at this pin puts the device into the multiplexed mode of operation where the "I" and "Q" data are multiplexed onto the "I" output bus and the "Q" output lines all remain at a logic low. 3.3 OFFSET CORRECT (OC) PIN The Offset Correct (OC) pin is used to initiate an offset correction sequence. This procedure should be done after power up and need not be performed again unless power to the ADC10D020 is interrupted. An independent offset correction sequence for each converter is initiated when there is a low-to-high transition at the OC pin. This sequence takes 34 clock cycles to complete, during which time 32 conversions are taken and averaged. The result is subtracted from subsequent conversions. Because the offset correction is performed digitally at the output of the ADC, the output range of the ADC is reduced by the offset amount. Each input pair should have a 0V differential voltage value during this entire 34 clock period, but the "I" and "Q" input
TABLE 1. ADC10D020 Input/Output Relationships GAIN 0 0 0 0 0 0 1 1 1 1 1 1 OF 0 0 0 1 1 1 0 0 0 1 1 1 I+/Q+ VCM + 0.25*VREF VCM VCM + 0.25*VREF VCM + 0.25*VREF VCM VCM + 0.25*VREF VCM + 0.5*VREF VCM VCM + 0.5*VREF VCM + 0.5*VREF VCM VCM + 0.5*VREF I-/Q- VCM - 0.25*VREF VCM VCM - 0.25*VREF VCM - 0.25*VREF VCM VCM - 0.25*VREF VCM - 0.5*VREF VCM VCM - 0.5*VREF VCM - 0.5*VREF VCM VCM - 0.5*VREF Output Code 11 1111 1111 10 0000 0000 00 0000 0000 01 1111 1111 00 0000 0000 10 0000 0000 11 1111 1111 10 0000 0000 00 0000 0000 01 1111 1111 00 0000 0000 10 0000 0000
29
www.national.com
Applications Information
5.0 POWER SUPPLY CONSIDERATIONS
(Continued)
A/D converters draw sufficient transient current to corrupt their own power supplies if not adequately bypassed. A 10 F to 50 F tantalum or aluminum electrolytic capacitor should be placed within half an inch (1.2 centimeters) of the A/D power pins, with a 0.1 F ceramic chip capacitor placed as close as possible to each of the converter's power supply pins. Leadless chip capacitors are preferred because they have low lead inductance. While a single voltage source should be used for the analog and digital supplies of the ADC10D020, these supply pins should be well isolated from each other to prevent any digital noise from being coupled to the analog power pins. A choke is recommended between the VA and VD supply lines. A choke should also be used between VA and DR VD when the same supply source is used for both VA and DR VD. Be sure to bypass DR VD. The DR VD pins are completely isolated from the other supply pins. Because of this isolation, a separate supply can be used for these pins. This DR VD supply can be significantly lower than the three volts used for the other supplies, easing the interface to lower voltage digital systems. Using a lower voltage for this supply can also reduce the power consumption and noise associated with the output drivers. The converter digital supply should not be the supply that is used for other digital circuitry on the board. It should be the same supply used for the ADC10D020 analog supply. As is the case with all high speed converters, the ADC10D020 should be assumed to have little high frequency power supply rejection. A clean analog power source should be used. No pin should ever have a voltage on it that is more than 300 mV in excess of the supply voltages or below ground, not even on a transient basis. This can be a problem upon application of power to a circuit and upon turn off of the power source. Be sure that the supplies to circuits driving the CLK, or any other digital or analog inputs do not come up any faster than does the voltage at the ADC10D020 power pins.
6.0 LAYOUT AND GROUNDING Proper routing of all signals and proper ground techniques are essential to ensure accurate conversion. Separate analog and digital ground planes may be used if adequate care is taken with signal routing, but may result in EMI/RFI. A single ground plane with proper component placement will yield good results while minimizing EMI/RFI. Analog and digital ground current paths should not coincide with each other as the common impedance will cause digital noise to be added to analog signals. Accordingly, traces carrying digital signals should be kept as far away from traces carrying analog signals as is possible. Power should be routed with traces rather than the use of a power plane. The analog and digital power traces should be kept well away from each other. All power to the ADC10D020 should be considered analog. The DR GND pin should be considered a digital ground and not be connected to the ground plane in close proximity with the other ground pins of the ADC10D020. Each bypass capacitor should be located as close to the appropriate converter pin as possible and connected to the pin and the appropriate ground plane with short traces. The analog input should be isolated from noisy signal traces to avoid coupling of spurious signals into the input. Any external component (e.g., a filter capacitor) connected between the converter's input and ground should be connected to a very clean point in the ground return. The clock line should be properly terminated, as discussed in Section 3.1, and be as short as possible.
Figure 8 gives an example of a suitable layout and bypass capacitor placement. All analog circuitry (input amplifiers, filters, reference components, etc.) and interconnections should be placed in an area reserved for analog circuitry. All digital circuitry and I/O lines should be placed in an area reserved for digital circuitry. Violating these rules can result in digital noise getting into the analog circuitry, which will degrade accuracy and dynamic performance (THD, SNR, SINAD).
www.national.com
30
Applications Information
(Continued)
20025575
FIGURE 8. An Acceptable Layout Pattern
31
www.national.com
Applications Information
7.0 DYNAMIC PERFORMANCE
(Continued)
The ADC10D020 is ac tested and its dynamic performance is guaranteed. To meet the published specifications, the clock source driving the CLK input must be free of jitter. For best dynamic performance, isolating the ADC clock from any digital circuitry should be done with adequate buffers, as with a clock tree. See Figure 9.
operation. It is not uncommon for high speed digital circuits (e.g., 74F and 74AC devices) to exhibit undershoot that goes a few hundred millivolts below ground. A resistor of 50 to 100 in series with the offending digital input, close to the source, will usually eliminate the problem. Care should be taken not to overdrive the inputs of the ADC10D020 (or any device) with a device that is powered from supplies outside the range of the ADC10D020 supply. Such practice may lead to conversion inaccuracies and even to device damage. Attempting to drive a high capacitance digital data bus. The more capacitance the output drivers has to charge for each conversion, the more instantaneous digital current is required from DR VD and DR GND. These large charging current spikes can couple into the analog section, degrading dynamic performance. Adequate bypassing and attention to board layout will reduce this problem. Buffering the digital data outputs (with a 74ACTQ821, for example) may be necessary if the data bus to be driven is heavily loaded. Dynamic performance can also be improved by adding series resistors of 47 to 56 at each digital output, close to the ADC output pins. Using a clock source with excessive jitter. This will cause the sampling interval to vary, causing excessive output noise and a reduction in SNR and SINAD performance. The use of simple gates with RC timing as a clock source is generally inadequate. Using the same voltage source for VD and digital logic. As mentioned in Section 5.0, VD should use the same power source used by VA and other analog components, but should be decoupled from VA.
20025576
FIGURE 9. Isolating the ADC Clock from Digital Circuitry 8.0 COMMON APPLICATION PITFALLS Driving the inputs (analog or digital) beyond the power supply rails. For proper operation, no input should not go more than 300 mV beyond the supply pins. Exceeding these limits on even a transient basis can cause faulty or erratic
www.national.com
32
ADC10D020 Dual 10-Bit, 20 MSPS, 150 mW A/D Converter
Physical Dimensions
inches (millimeters) unless otherwise noted
48-Lead TQFP Package Ordering Number ADC10D020CIVS NS Package Number VBA48A
NOTES UNLESS OTHERWISE SPECIFIED 1. STANDARD LEAD FINISH 7.62 MICROMETERS MINIMUM SOLDER PLATING (85/15) THICKNESS ON ALLOY 42/COPPER. 2. DIMENSION DOES NOT INCLUDE MOLD PROTRUSION. MAXIMUM ALLOWABLE MOLD PROTRUSION 0.15 mm PER SIDE. 3. REFERENCE JEDEC REGISTRATION MS-026, VARIATION ABC, DATED FEBRUARY 1999.
LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user.
National Semiconductor Corporation Americas Email: support@nsc.com National Semiconductor Europe Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Francais Tel: +33 (0) 1 41 91 8790
2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness.
National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: ap.support@nsc.com
National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Fax: 81-3-5639-7507
www.national.com
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

▲Up To Search▲

Price & Availability of ADC10D020

	To Download ADC10D020 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .