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a
FEATURES Supports DOCSIS Standard for Reverse Path Transmission Gain Programmable in 6.02 dB Steps over a 48.16 dB Range Low Distortion at 60 dBmV Output -63 dBc SFDR at 21 MHz -57 dBc SFDR at 42 MHz Output Noise Level -47 dBmV in 160 kHz Maintains 75 Output Impedance Transmit Enable and Transmit Disable Modes Upper Bandwidth: 160 MHz (Full Gain Range) 5 V Supply Operation Supports SPI Interfaces APPLICATIONS Gain-Programmable Line Driver DOCSIS High-Speed Data Modems Interactive Cable Set-Top Boxes PC Plug-in Cable Modems General-Purpose Digitally Controlled Variable Gain Block
5 V CATV Line Driver Coarse Step Output Power Control AD8327
FUNCTIONAL BLOCK DIAGRAM
VCC (5 PINS) BYP
R1
AD8327
VIN+
VIN-
DIFF OR SINGLE INPUT AMP
VERNIER
ATTENUATION CORE
POWER AMP
ZOUT = 75
VOUT
8 R2
ZIN (SINGLE) = 800 ZIN (DIFF) = 1.6k
DECODE 8 DATA LATCH 8
SHIFT REGISTER POWER-DOWN LOGIC
CXR
DATEN
DATA
CLK
GND (5 PINS)
TXEN
SLEEP
GENERAL DESCRIPTION
-50 VOUT = 60dBmV @ MAX GAIN -55
DISTORTION - dBc
The AD8327 is a low-cost, digitally controlled, variable gain amplifier optimized for coaxial line driving applications such as cable modems that are designed to the MCNS-DOCSIS upstream standard. An 8-bit serial word determines the desired output gain over a 48.16 dB range resulting in gain changes of 6.02 dB/major carry. The AD8327 comprises a digitally controlled variable attenuator of 0 dB to -48.16 dB, which is preceded by a low noise, fixed gain buffer and followed by a low distortion, high power amplifier. The AD8327 accepts a differential or single-ended input signal. The output is specified for driving a 75 load, such as coaxial cable. Distortion performance of -63 dBc is achieved with an output level up to 60 dBmV at 21 MHz bandwidth. A key performance and cost advantage of the AD8327 results from the ability to maintain a constant 75 output impedance during Transmit Enable and Transmit Disable conditions. In addition, this device has a sleep mode function that reduces the quiescent current to 5 mA. The AD8327 is packaged in a low-cost 20-lead TSSOP, operates from a single 5 V supply, and has an operational temperature range of -40C to +85C.
HD3 -60 HD2 -65
-70
-75 5 15 25 35 45 55 FUNDAMENTAL FREQUENCY - MHz 65
Figure 1. Harmonic Distortion vs. Frequency
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Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 2001
AD8327-SPECIFICATIONS (T = 25 C, V = 5 V, R = 75
A S L
, VIN(DIFFERENTIAL) = 30 dBmV)
Min Typ 30 13.2 800 1600 2 47.16 29 -19.16 48.16 30 -18.16 6.02 Max Unit dBmV dB pF 49.16 dB 31 dB -17.16 dB dB/Major Carry MHz dB dB dBmV in 160 kHz dBmV in 160 kHz dBmV in 160 kHz dBm dBc dBc dBc dBc dBc dBc dBc dB ns ns dBc
Parameter INPUT CHARACTERISTICS Specified AC Voltage Noise Figure Input Resistance Input Capacitance GAIN CONTROL INTERFACE Gain Range Maximum Gain Minimum Gain Gain Scaling Factor OUTPUT CHARACTERISTICS Bandwidth (-3 dB) Bandwidth Roll-Off Bandwidth Peaking Output Noise Spectral Density
Conditions POUT = 60 dBmV, Max Gain Max Gain, f = 10 MHz Single-Ended Input Differential Input
Gain Code = 10000000 (128 Decimal) Gain Code = 00000000 (0 Decimal)
All Gain Codes f = 65 MHz All Gain Codes Max Gain, f = 10 MHz Min Gain, f = 10 MHz Transmit Disable Mode (TXEN = 0), f = 10 MHz Max Gain, f = 10 MHz Transmit Enable (TXEN = 1) and Transmit Disable Mode (TXEN = 0) f = 21 MHz, VOUT = 60 dBmV @ Max Gain f = 42 MHz, VOUT = 60 dBmV @ Max Gain f = 65 MHz, VOUT = 60 dBmV @ Max Gain f = 21 MHz, VOUT = 60 dBmV @ Max Gain f = 42 MHz, VOUT = 60 dBmV @ Max Gain f = 65 MHz, VOUT = 60 dBmV @ Max Gain Adjacent Channel Width = Transmit Channel Width = 160 KSYM/SEC f = 10 MHz, Code to Code Min to Max Gain Max Gain, VIN = 30 dBmV Max Gain, TXEN = 0 V, f = 42 MHz, VIN = 30 dBmV Max Gain, VIN = 0 V Max Gain, VIN = 0 V Max Gain, VIN = 0 V Max Gain, VIN = 0 V Equivalent Output = 31 dBmV Equivalent Output = 60 dBmV
160 0.4 0 -32 -47 -66 14.8 75 20% -63 -61 -54 -63 -57 -57 -62 0.25 60 30 -52
1 dB Compression Point Differential Output Impedance OVERALL PERFORMANCE Second Order Harmonic Distortion Third Order Harmonic Distortion Adjacent Channel Power Gain Linearity Error Output Settling Due to Gain Change (TGS) Due to Input Change Isolation in Transmit Disable Mode POWER CONTROL Transmit Enable Settling Time (TON)1 Transmit Disable Settling Time (TOFF)1 Transmit Enable Settling Time (TON)2 Transmit Disable Settling Time (TOFF)2 Between Burst Transients2 Ramp Setting2 POWER SUPPLY Operating Range Quiescent Current
300 40 2 1.7 3 25 2 4.75 75 40 10 3 -40 5 105 60 15 5 5.25 135 80 20 7 +85
ns ns s s mV p-p mV p-p s V mA mA mA mA C
Transmit Enable Mode (TXEN = 1) @ Dec 128 Transmit Enable Mode (TXEN = 1) @ Dec 0 Transmit Disable Mode @ All Gain Codes Sleep Mode @ All Gain Codes
OPERATING TEMPERATURE RANGE
NOTES 1 For Transmit Enable or Transmit Disable transitions using a 0 pF capacitor (at CXR pin) to ground. 2 For Transmit Enable or Transmit Disable transitions using a 100 pF capacitor (at CXR pin) to ground. Specifications subject to change without notice.
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AD8327 LOGIC INPUTS (TTL/CMOS-Compatible Logic) (DATEN, CLK, SDATA, TXEN, SLEEP, V
Parameter Logic "1" Voltage Logic "0" Voltage Logic "1" Current (VINH = 5 V) CLK, SDATA, DATEN Logic "0" Current (VINL = 0 V) CLK, SDATA, DATEN Logic "1" Current (VINH = 5 V) TXEN Logic "0" Current (VINL = 0 V) TXEN Logic "1" Current (VINH = 5 V) SLEEP Logic "0" Current (VINL = 0 V) SLEEP Min 2.1 0 0 -600 50 -250 50 -250 Typ
CC
= 5 V: Full Temperature Range)
Max 5.0 0.8 20 -100 190 -30 190 -30 Unit V V nA nA A A A A
TIMING REQUIREMENTS
Parameter
(Full Temperature Range, VCC = 5 V, tR = tF = 4 ns, fCLK = 8 MHz unless otherwise noted.)
Min 16.0 32.0 5.0 15.0 5.0 3.0 10 Typ Max Unit ns ns ns ns ns ns ns
Clock Pulsewidth (tWH) Clock Period (tC) Setup Time SDATA vs. Clock (tDS) Setup Time DATEN vs. Clock (tES) Hold Time SDATA vs. Clock (tDH) Hold Time DATEN vs. Clock (tEH) Input Rise and Fall Times, SDATA, DATEN, Clock (tR, tF)
tDS
VALID DATA WORD G1 MSB. . . .LSB
SDATA
VALID DATA WORD G2
tC tWH
CLK
tES
DATEN 8 CLOCK CYCLES
tEH
GAIN TRANSFER (G1)
GAIN TRANSFER (G2)
tOFF
TXEN
tGS tON
ANALOG OUTPUT SIGNAL AMPLITUDE (p-p)
Figure 2. Serial Interface Timing
VALID DATA BIT
SDATA MSB
MSB-1
MSB-2
tDS
CLK
tDH
Figure 3. SDATA Timing
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AD8327
ABSOLUTE MAXIMUM RATINGS* PIN CONFIGURATION
SDATA CLK TXEN VCC GND VCC CXR GND GND
1 2 3 4 5 20 19 18
Supply Voltage +VS Pins 4, 6, 11, 12, 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 V Input Voltages Pins 17, 18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5 V Pins 1, 2, 3, 19, 20 . . . . . . . . . . . . . . . . . . . -0.8 V to +5.5 V Internal Power Dissipation TSSOP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 810 mW Operating Temperature Range . . . . . . . . . . . -40C to +85C Storage Temperature Range . . . . . . . . . . . . -65C to +150C Lead Temperature, Soldering 60 seconds . . . . . . . . . . . 300C
*Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
DATEN SLEEP VIN- VIN+
16 VCC TOP VIEW 6 (Not to Scale) 15 GND 7 8 9 14 BYP 13 GND 12 11
AD8327
17
VCC VCC
VOUT 10
PIN FUNCTION DESCRIPTIONS
Pin No. 1 2
Mnemonic SDATA CLK
Description Serial Data Input. This digital input allows for an 8-bit serial (gain) word to be loaded into the internal register with the MSB (Most Significant Bit) first. Clock Input. The clock port controls the serial attenuator data transfer rate to the 8-bit masterslave register. A Logic 0-to-1 transition latches the data bit and a 1-to-0 transfers the data bit to the slave. This requires the input serial data word to be valid at or before this clock transition. Logic "0" disables transmission. Logic "1" enables transmission. Common Positive External Supply Voltage. A 0.1 F capacitor must decouple each pin. Common External Ground Reference Transmit Enable/Disable Timing Capacitor. This pin is decoupled with a 100 pF capacitor to GND. Output Signal Internal Bypass. This pin must be externally ac-coupled (0.1 F capacitor). Noninverting Input. DC-biased to approximately VCC/2. Should be ac-coupled with a 0.1 F capacitor. Inverting Input. DC-biased to approximately VCC/2. Should be ac-coupled with a 0.1 F capacitor. Low Power Sleep Mode. Logic 0 enables Sleep mode, where ZOUT goes to 200 and supply current is reduced to 5 mA. Logic 1 enables normal operation. Data Enable Low Input. This port controls the 8-bit parallel data latch and shift register. A Logic 0-to-1 transition transfers the latched data to the attenuator core (updates the gain) and simultaneously inhibits serial data transfer into the register. A 1-to-0 transition inhibits the data latch (holds the previous gain state) and simultaneously enables the register for serial data load.
3 4, 6, 11, 12, 16 5, 8, 9, 13, 15 7 10 14 17 18 19 20
TXEN VCC GND CXR VOUT BYP VIN+ VIN- SLEEP DATEN
ORDERING GUIDE
Model AD8327ARU AD8327ARU-REEL AD8327-EVAL
Temperature Range -40C to +85C -40C to +85C
Package Description 20-Lead TSSOP 20-Lead TSSOP Evaluation Board
JA
Package Option RU-20 RU-20
85C/W* 85C/W*
*Thermal Resistance measured on SEMI standard 4-layer board.
CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD8327 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
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Typical Performance Characteristics-AD8327
0
+VS 10 F
-10 -20
TXEN = 0 VIN = 30dBmV
0.1 F 0.1 F VIN- VIN 165 VIN+ 0.1 F BYP CXR 0.1 F 100pF GND VCC
ISOLATION - dBc
75
-30 -40 -50 -60 -70 -80 MIN GAIN -90 1 100 10 FREQUENCY - MHz 1000 MAX GAIN
AD8327
0.1 F
TPC 1. Basic Test Circuit
TPC 4. Isolation in Transmit Disable Mode vs. Frequency
40
0.6 0.5 0.4
f = 65MHz
30 20
128D 64D 32D 16D
GAIN ERROR - dB
0.3 GAIN - dB 0.2 0.1 0 -0.1
f = 42MHz
10 0
08D 04D 02D
f = 10MHz f = 5MHz
-10 -20
01D 00D
-0.2 -0.3 0 16 32 48 64 80 96 GAIN CONTROL - Decimal Code 112 128
-30 1 10 100 FREQUENCY - MHz 1000
TPC 2. Gain Error vs. Gain Control
TPC 5. AC Response
160 155 150 TXEN = 1 145 TXEN = 0
90 85 80 TXEN = 0
IMPEDANCE -
IMPEDANCE -
140 135
+VS
75 70 65
TXEN = 1
130 125 120 115 1
VIN
0.1 F VIN- 165 VIN+ 0.1 F
AD8327
GND
OUT
0.1 F
75
60 55
10 FREQUENCY - MHz
100
1
10 FREQUENCY - MHz
100
TPC 3. Input Impedance vs. Frequency
TPC 6. Output Impedance vs. Frequency
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AD8327
-50
-50 VOUT = 60dBmV @ MAX GAIN -55
-55
DISTORTION - dBc
VOUT = 61dBmV @ MAX GAIN
DISTORTION - dBc
-60
VOUT = 61dBmV @ MAX GAIN
-60
VOUT = 60dBmV @ MAX GAIN
-65 VOUT = 59dBmV @ MAX GAIN -70
-65 VOUT = 58dBmV @ MAX GAIN -70
VOUT = 59dBmV @ MAX GAIN
-75
VOUT = 58dBmV @ MAX GAIN
-80
5
15
25 35 45 55 FUNDAMENTAL FREQUENCY - MHz
65
5
15
25 35 45 55 FUNDAMENTAL FREQUENCY - MHz
65
TPC 7. Second Order Harmonic Distortion vs. Frequency for Various Output Levels
TPC 10. Third Order Harmonic Distortion vs. Frequency for Various Output Levels
-50 -55 -60 FO = 5MHz VOUT = 60dBmV @ MAX GAIN
-50 -55 -60 FO = 21MHz VOUT = 60dBmV @ MAX GAIN
DISTORTION - dBc
-65 -70 -75 -80 -85 -90
DISTORTION - dBc
HD2
-65 -70 -75
HD2
HD3 -80 -85 -90 0 16 32 48 64 80 96 GAIN CONTROL - Decimal Code 112 128
HD3
0
16
32 48 64 80 96 GAIN CONTROL - Decimal Code
112
128
TPC 8. Harmonic Distortion vs. Gain Control
TPC 11. Harmonic Distortion vs. Gain Control
-50 -55 -60
DISTORTION - dBc
-50
FO = 42MHz VOUT = 60dBmV @ MAX GAIN
-55 -60
FO = 65MHz VOUT = 60dBmV @ MAX GAIN HD2
HD2 -65 -70 -75 -80 -85 -90
DISTORTION - dBc
-65 -70 -75 -80 -85 -90
HD3
HD3
0
16
32 48 64 80 96 GAIN CONTROL - Decimal Code
112
128
0
16
32 48 64 80 96 GAIN CONTROL - Decimal Code
112
128
TPC 9. Harmonic Distortion vs. Gain Control
TPC 12. Harmonic Distortion vs. Gain Control
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AD8327
-10 -20 -30 -40 -50
VOUT - dBmV
60
CH PWR ACP UP ACP LOW 9.0dBm -62dBc -62.5dBc
50 40 30 20 10 0 -10 -20
VOUT = 60dBmV @ MAX GAIN
-60 -70 -80 -90 -100 C11 -110 CENTER 21MHz C11 C0 C0 Cu1 Cu1
-30 -40 41.0
75kHz/DIV
SPAN 750kHz
41.2
41.4
41.6
41.8 42.0 42.2 42.4 FREQUENCY - MHz
42.6
42.8
43.0
TPC 13. Adjacent Channel Power
TPC 16. Two-Tone Intermodulation Distortion
-30
-25
f = 10MHz
TXEN = 1 OUTPUT NOISE - dBmV in 160kHz -34
OUTPUT NOISE - dBmV in 160kHz
-30 -35 -40 -45 -50 -55 -60 -65 -70
@ MAX GAIN, TXEN = 1
-38
@ MIN GAIN, TXEN = 1
-42
-46
ALL GAIN CODES, TXEN = 0
-50 0 16 32 48 64 80 96 GAIN CONTROL - Decimal Code 112 128
-75 5 15 25 35 45 FREQUENCY - MHz 55 65
TPC 14. Output Referred Noise vs. Gain Control
TPC 17. Output Referred Noise vs. Frequency for Various Gain Codes
35 VOUT = 60dBmV @ MAX GAIN 30 CL = 10pF CL = 0pF
QUIESCENT SUPPLY CURRENT - mA
120 TXEN = 1 110
100
GAIN - dB
25
+VS
10 F
CL = 20pF
90
20
0.1 F
0.1 F
80
VCC VIN-
0.1 F
VIN
165
AD8327
VIN+ CL GND 100pF BYP CXR
70
15
0.1 F
0.1 F
75
60 50 0 16 32 48 64 80 96 GAIN CONTROL - Decimal Code 112 128
CL = 50pF 10 1 100 10 FREQUENCY - MHz 1000
TPC 15. AC Response for Various Capacitor Loads
TPC 18. Supply Current vs. Gain Code
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AD8327
APPLICATIONS General Application
The AD8327 is primarily intended for use as the upstream power amplifier (PA), also known as a line driver, in DOCSIS (Data Over Cable Service Interface Specification) certified cable modems and CATV set-top boxes. The upstream signal is either a QPSK or QAM signal generated by a DSP, a dedicated QPSK/ QAM modulator, or a DAC. In all cases the signal must be low-pass filtered before being applied to the PA in order to filter out-of-band noise and higher order harmonics from the amplified signal. Due to the varying distances between the cable modem and the headend, the upstream PA must be capable of varying the output power by applying gain or attenuation. The varying output power of the AD8327 ensures that the signal from the cable modem will have the proper level once it arrives at the headend. The upstream signal path commonly includes a diplexer and cable splitters. The AD8327 has been designed to overcome losses associated with these passive components in the upstream cable path.
Circuit Description
which amplifies these currents to the appropriate levels necessary to drive a 75 load. The output stage maintains 75 output impedance, eliminating the need for external matching resistors.
SPI Programming and Gain Adjustment
The AD8327 is composed of three analog functions in the powerup or forward mode. The input amplifier (preamp) can be used single-ended or differentially. If the input is used in the differential configuration, it is imperative that the input signals be 180 degrees out of phase and of equal amplitude. The preamp stage drives a DAC, which provides the AD8327's attenuation (eight bits or 48.16 dB). The signals in the preamp and DAC gain blocks are differential to improve the PSRR and linearity. A differential current is fed from the DAC into the output stage,
The AD8327 is controlled through a serial peripheral interface (SPI) of three digital data lines: CLK, DATEN, and SDATA. Changing the gain requires eight bits of data to be streamed into the SDATA port. The sequence of loading the SDATA register begins on the falling edge of the DATEN pin, which activates the CLK line. With the CLK line activated, data on the SDATA line is clocked into the serial shift register, Most Significant Bit (MSB) first, on the rising edge of the CLK pulses. The 8-bit data word is latched into the attenuator core on the rising edge of the DATEN line. This provides control over the changes in the output signal level. The serial interface timing for the AD8327 is shown in Figures 2 and 3. The programmable gain range of the AD8327 is -18.16 dB to +30 dB with steps of 6.02 dB per major carry. This provides a total gain range of 48.16 dB. The AD8327 was characterized with a TOKO transformer (TOKO#617DB-A0070) on the input, and the stated gain values account for the losses due to the transformer. Table I shows the possible gain states.
Input Bias, Impedance, and Termination
The VIN+ and VIN- inputs have a dc bias level of VCC/2, therefore the input signal should be ac-coupled using 0.1 F capacitors as seen in the typical application circuit (see Figure 4). The differential input impedance of the AD8327 is approximately 1.6 k, while the single-ended input impedance is 800 .
Table I. Gain States
Decimal Code 0 1 2 4 8 16 32 64 128
Bit 7 0 0 0 0 0 0 0 0 1
Bit 6 0 0 0 0 0 0 0 1 0
Bit 5 0 0 0 0 0 0 1 0 0
Bit 4 0 0 0 0 0 1 0 0 0
Bit 3 0 0 0 0 1 0 0 0 0
Bit 2 0 0 0 1 0 0 0 0 0
Bit 1 0 0 1 0 0 0 0 0 0
Bit 0 0 1 0 0 0 0 0 0 0
Gain -18.16 -12.14 -6.12 -0.10 5.92 11.94 17.96 23.98 30
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AD8327
VCC 10 F SLEEP ENB SDATA CLK TXEN 0.1 F 0.1 F 100pF 1 2 3 4 5 6 7 8 9 10 0.1 F 20 19 18 17 16 15 14 13 12 11 0.1 F 0.1 F 0.1 F 0.1 F 0.1 F VIN+ ZIN = 150 165 VIN-
AD8327
SDATA CLK TXEN VCC GND VCC CXR GND GND VOUT ENB SLEEP VIN- VIN+ VCC GND BYP GND VCC VCC
0.1 F
TO DIPLEXER ZIN = 75
Figure 4. Typical Application Circuit
Single-Ended Inverting Input
R13 =
ZIN 1600
1600 - ZIN
When operating the AD8327 in a single-ended input mode VIN+ and VIN- should be terminated as illustrated in Figure 5. On the AD8327 evaluation boards, this termination method requires the removal of R13-R16 and R20, as well as the addition of a 0 jumper at R17. Table II shows the correct values for R11 and R12 for some common input configurations. Other input impedance configurations may be accommodated using the equations in Figure 5. The inverting and noninverting inputs of the AD8327 must be balanced for all input configurations
R12 = ZIN 800 800 - ZIN R11 = ZIN R12 R12 + ZIN - R12 + ZIN R11
VIN+ R13 ZIN
AD8327
Figure 6. Single to Differential Input
Differential Signal Source
The AD8327 evaluation board is also capable of accepting a differential input signal. Remove R11-R12, R14-R15, and R20, and place 0 jumpers for R16-R17. See Table II for common values of R13, or calculate other input configurations using the equation in Figure 7.
R13 = ZIN 1600 1600 - ZIN
AD8327
Figure 5. Single-Ended Inverting Input
Differential Input from Single-Ended Source
VIN+ ZIN VIN- R13
AD8327
The default configuration of the evaluation board implements a differential signal drive from a single-ended signal source. A TOKO 1:1 transformer is included on the board for this purpose (T3). Enabling the evaluation board for single to differential input conversion requires R11-R12 and R16-R17 to be removed, and 0 jumpers must be installed on the placeholders for R14, R15, and R20. Table II provides typical R13 values for common input configurations. Other input impedances may be calculated using the equation in Figure 6. Refer to Figure 10 for evaluation board schematic. To utilize the transformer for converting a singleended source into a differential signal, the input signal must be applied to VIN+.
Figure 7. Differential Input
Output Bias, Impedance, and Termination
The output of the AD8327 has a dc bias level of approximately VCC/2; therefore, it should be ac-coupled before being applied to the load. The output impedance of the AD8327 is internally maintained at 75 , regardless of whether the amplifier is in transmit enable or transmit disable mode. This eliminates the need for external back termination resistors. If the output signal is being evaluated using standard 50 test equipment, a minimum loss 75 to 50 pad must be used to provide the test circuit with the proper impedance match.
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AD8327
Table II. Common Input Terminations Asynchronous Power-Down
Differential Input Termination ZIN ( ) 50 75 100 150 ZIN ( ) 50 75
Power Supply
R11 Open Open Open Open R11 ( ) 25.5 39.2
R12 Open Open Open Open R12 ( ) 53.6 82.5
R13 ( ) 52.1 78.7 107 165 R13 Open Open
Single-Ended Input Termination
The asynchronous TXEN pin is used to place the AD8327 into between-burst mode, while maintaining a differential output impedance of 75 . Applying Logic 0 to the TXEN pin activates the on-chip reverse amplifier, providing an 86% reduction in consumed power. For 5 V operation, the supply current is typically reduced from 105 mA to 15 mA. In this mode of operation, between-burst noise is minimized and the amplifier can no longer transmit in the upstream direction. In addition to the TXEN pin, the AD8327 also incorporates an asynchronous SLEEP pin, which may be used to further reduce the supply current to approximately 5 mA. Applying Logic 0 to the SLEEP pin places the amplifier into SLEEP mode. Transitioning into or out of SLEEP mode may result in a transient voltage at the output of the amplifier.
Distortion, Adjacent Channel Power, and DOCSIS
The 5 V supply should be delivered to each of the VCC pins via a low impedance power bus to ensure that each pin is at the same potential. The power bus should be decoupled to ground using a 10 F tantalum capacitor located close to the AD8327ARU. In addition to the 10 F capacitor, each VCC pin should be individually decoupled to ground with 0.1 F ceramic chip capacitors located close to the pins. The bypass pin, labeled BYP (Pin 14), should also be decoupled with a 0.1 F capacitor. The PCB should have a low impedance ground plane covering all unused portions of the board, except in areas of the board where input and output traces are in close proximity to the AD8327. All AD8327 ground pins must be connected to the ground plane to ensure proper grounding of all internal nodes.
CXR Pin
The AD8327 features internal circuitry that controls burst transients. This feature uses a 100 pF capacitor connected to Pin 7 of the AD8327, to slow down the turn-on transient and minimize between-burst transients.
Signal Integrity Layout Considerations
In order to deliver the DOCSIS required +58 dBmV of QPSK signal and +55 dBmV of 16 QAM signal, the PA is required to deliver up to +60 dBmV and +57 dBmV respectively. This level is required to compensate for losses associated with the diplex filter or other passive components that may be included in the upstream path of cable modems or set-top boxes. It should be noted that the AD8327 was characterized with the TOKO 617DB-A0070 transformer on the input to generate a differential input signal. TPC 7 and TPC 10 show the AD8327 second and third order harmonic distortion performance versus fundamental frequency for various output power levels. These figures are useful for determining the in-band harmonic levels from 5 MHz to 65 MHz. Harmonics higher in frequency (above 42 MHz for DOCSIS and above 65 MHz for EuroDOCSIS) will be sharply attenuated by the low-pass filter function of the diplexer. Another measure of signal integrity is adjacent channel power, commonly referred to as ACP. DOCSIS section 4.2.10.1.1 states, "Spurious emissions from a transmitted carrier may occur in an adjacent channel that could be occupied by a carrier of the same or different symbol rates." TPC 13 shows the measured ACP for a +57 dBmV 16 QAM signal taken at the output of the AD8327 evaluation board, through a 75 to 50 matching pad (5.7 dB of loss). The transmit channel width and adjacent channel width in TPC 13 correspond to symbol rates of 160 KSYM/S. Table III shows the ACP results for the AD8327 driving a 16 QAM, +57 dBmV signal for all conditions in DOCSIS Table 4-7 "Adjacent Channel Spurious Emissions."
Table III. Adjacent Channel Power
ADJACENT CHANNEL SYMBOL RATE TRANSMIT SYMBOL RATE 160 KSYM/SEC 320 KSYM/SEC 640 KSYM/SEC 1280 KSYM/SEC 2560 KSYM/SEC 160 KSYM/SEC 320 KSYM/SEC 640 KSYM/SEC 1280 KSYM/SEC 2560 KSYM/SEC ACP (dBc) -62 -62 -63 -64 -66 ACP (dBc) -63 -63 -62 -63 -63 ACP (dBc) -65 -64 -63 -63 -63 ACP (dBc) -66 -66 -65 -63 -62 ACP (dBc) -66 -66 -66 -64 -63
Careful attention to printed circuit board layout details will prevent problems due to board parasitics. Proper RF design techniques are mandatory. The differential input and output traces should be kept as short as possible. It is also critical that all differential signal paths be symmetrical in length and width. In addition, the input and output traces should be kept far apart, to minimize coupling (crosstalk) through the board. Following these guidelines will optimize the overall performance of the AD8327 in all applications.
Initial Power-Up
When the supply voltage is first applied to the AD8327, the gain of the amplifier is initially set to gain code 0. As power is first applied to the amplifier, the TXEN pin should be held low (Logic 0) to prevent forward signal transmission. After power has been applied to the amplifier, the gain can be set to the desired level by following the procedure provided in the SPI Programming and Gain Adjustment section. The TXEN pin can then be brought from Logic 0 to Logic 1, enabling forward signal transmission at the desired gain level.
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AD8327
Noise and DOCSIS Running AD8327 Software
At minimum gain, the AD8327 output noise spectral density is 11 nV/Hz measured at 10 MHz. DOCSIS Table 4-8,"Spurious Emissions in 5 MHz to 42 MHz," specifies the output noise for various symbol rates. The calculated noise in dBmV for 160KSYM/SECOND is:
2 20 log 11 nV x 160 kHz + 60 = -47 dBmV Hz
To load the control software, go to START, PROGRAMS, CABDRIVE_27, or select the AD8327.exe from the installed directory. Once loaded, select the proper parallel port to communicate with the AD8327 (Figure 8).
Comparing the computed noise power of -47 dBmV to the +8 dBmV signal yields -55 dBc, which meets the required level set forth in DOCSIS Table 4-8. As the AD8327 gain is increased above this minimum value, the output signal increases at a faster rate than the noise, resulting in a signal to noise ratio that improves with gain. In transmit disable mode, the output noise spectral density is 1.3 nV/Hz, which results in -66 dBmV when computed over 160 KSYM/S. The noise power was measured directly at the output of the AD8327AR-EVAL board.
Evaluation Board Features and Operation
The AD8327 evaluation board (Part #AD8327AR-EVAL) and control software can be used to control the AD8327 upstream cable driver via the parallel port of a PC. A standard printer cable connected between the parallel port of the personal computer is used to feed all the necessary data to the AD8327 using the Windows-based control software. This package provides a means of evaluating the amplifier with a convenient way to program the gain/attenuation, as well as offering easy control of the asynchronous TXEN and SLEEP pins. With this evaluation kit, the AD8327 can be evaluated in either a single-ended or differential input configuration. A schematic of the evaluation board is provided in Figure 10.
Overshoot on PC Printer Ports
Figure 8. Parallel Port Selection
Controlling Gain/Attenuation of the AD8327
The slide bar controls the gain/attenuation of the AD8327, which is displayed in dB and in V/V. The gain scales 6 dB per major carry. The gain code from the position of the slide bar is displayed in decimal, binary, and hexadecimal (Figure 9).
The data lines on some PC parallel printer ports have excessive overshoot that may cause communications problems when presented to the CLK pin of the AD8327. The evaluation board was designed to accommodate a series resistor and shunt capacitor (R2 and C5 in Figure 10) to filter the CLK signal if required.
Installing Visual Basic Control Software
Install the "CabDrive_27" software by running "setup.exe" on disk one of the AD8327 Evaluation Software. Follow on-screen directions and insert disk two when prompted. Choose installation directory, and then select the icon in the upper left to complete installation.
Figure 9. Control Software Interface
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Transmit Enable and Sleep Mode Memory Functions
The Transmit Enable and Transmit Disable buttons select the mode of operation of the AD8327 by asserting logic levels on the asynchronous TXEN pin. The Transmit Disable button applies Logic 0 to the TXEN pin, disabling forward transmission while maintaining a 75 back termination. The Transmit Enable button applies Logic 1 to the TXEN pin, enabling the AD8327 for forward transmission. Checking the "Enable SLEEP Mode" checkbox applies logic "0" to the asynchronous SLEEP pin, setting the AD8327 for SLEEP mode.
The MEMORY section of the software provides a way to alternate between two gain settings. The "X->M1" button stores the current value of the gain slide bar into memory while the "RM1" button recalls the stored value, returning the gain slide bar to the stored level. The same applies to the "X->M2" and "RM2" buttons.
DATEN SDATA
TP9 VCC C12 10 F TP10 TP11 TP12 AGND Z1 AGND 1 2 3 4 5 6 7 8 9 10 TP2 TSSOP20 SDATA DATEN 20 SLEEP 19 CLK TXEN VIN- 18 VIN+ 17 VCC GND VCC 16 GND 15 VCC BYP 14 CXR GND 13 GND VCC 12 GND VCC 11 VOUT C11 0.1 F C16 0.1 F R12 DNI AGND TP23 R17 DNI R19 DNI VIN- R15 0
4 T4 3 2
CLK TXEN SLEEP
AGND
4 T3 6 2 3 1
R21 DNI AGND
C1 0.1 F C2 0.1 F
TP1
R13 78.7 C10 0.1 F C8 0.1 F C7 0.1 F AGND C15 0.1 F R11 DNI AGND TP24 R14 0
5
1
PRI SEC
PRI SEC
DNI
TOKO1
R20 0 VIN+
R16 DNI TP22 0
C3 100pF AGND TP3 R1 0 TP4 TP6 VCC
HPF
9
TB1 AGND
1
HPP LPP CBL
5
TP21
P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
P1 P1
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
DEVICE = 2LUGPWR
TP5
C4 DNI
P1 P1 P1 P1
COM CX6002 3 10-18 DNI AGND R6 DNI R7 0 R8 DNI TP20 CABLE R9 0 R10 DNI
TP14
TP16
R2 0
C5 DNI
P1 P1 P1 P1
C14 0.1 F
TP7
R3 0
TP8
P1 P1 P1
C6 DNI
P1 P1 P1 P1 P1
R5 DNI AGND
TP15
AGND
AGND
Figure 10. Evaluation Board Schematic
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Figure 11. Evaluation Board Layout--Top Silkscreen
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Figure 12. Evaluation Board Layout--Component Side
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Figure 13. Evaluation Board Layout--Internal Ground Plane
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Figure 14. Evaluation Board Layout--Internal Power and Ground Plane
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Figure 15. Evaluation Board Layout--Circuit Side
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Figure 16. Evaluation Board Layout--Bottom Silkscreen
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EVALUATION BOARD BILL OF MATERIALS
AD8327 Evaluation Board Rev. B, Single-Ended-to-Differential Input--Revised-February 21, 2001 Qty. 1 1 2 7 11 1 2 1 1 1 1 4 1 1 1 1 4 4 2 2 2 2 Description 10 F 25 V. `D' size tantalum chip capacitor 100 pF 0603 ceramic chip capacitor 0.1 F 50 V. 1206 size ceramic chip capacitor 0.1 F 25 V. 0603 size ceramic chip capacitor 0 5% 1/8 W. 1206 size chip resistor 78.7 1% 1/8 W. 1206 size chip resistor Yellow Test Point Red Test Point Black Test Point Centronics-type 36-pin Right-Angle Connector Terminal Block 2-Pos Green ED1973-ND SMA End launch Jack (E F JOHNSON # 142-0701-801) 1:1 Transformer TOKO # 617DB - A0070 PULSE Diplexer* AD8327 (TSSOP) UPSTREAM Cable Driver AD8327 REV. C Evaluation PC board #4-40 x 1/4 inch STAINLESS panhead machine screw #4-40 x 3/4 inch long aluminum round stand-off # 2-56 x 3/8 inch STAINLESS panhead machine screw # 2 steel flat washer # 2 steel internal tooth lockwasher # 2 STAINLESS STEEL hex. machine nut Ref Description C12 C3 C15, C16 C1, C2, C7-C11 R1-R3, R7, R9, R14, R15, R20 R13 TP23, TP24 TP9 TP10-TP12 (GND) P1 TB1 VIN-, VIN+, CABLE_0, HPF T3 Z2 Z1 Evaluation PC board
(P1 Hardware) (P1 Hardware) (P1 Hardware) (P1 Hardware)
NOTES *PULSE Diplexer part numbers B5008 (42 MHz), CX6002 (42 MHz), B5009 (65 MHz). DO NOT INSTALL C4, C5, C6, R6, R7, R8, R10-R12, R16, R17, R21, T9, TP1-TP8, TP14-TP16, TP20-TP22. SMA's TXEN, CLK, SLEEP, DATEN, SDATA, HPF_0, Z2.
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OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
20-Lead TSSOP (RU-20)
0.260 (6.60) 0.252 (6.40)
20
11
0.177 (4.50) 0.169 (4.30) 0.256 (6.50) 0.246 (6.25)
1 10
PIN 1 0.006 (0.15) 0.002 (0.05) 0.0433 (1.10) MAX
SEATING PLANE
0.0256 (0.65) 0.0118 (0.30) BSC 0.0075 (0.19)
0.0079 (0.20) 0.0035 (0.090)
8 0
0.028 (0.70) 0.020 (0.50)
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PRINTED IN U.S.A.
C02653-.8-10/01(0)

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