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5 V Upstream Cable Line Driver AD8328
FEATURES
Supports DOCSIS and EuroDOCSIS standards for reverse path transmission systems Gain programmable in 1 dB steps over a 59 dB range Low distortion at 60 dBmV output -57.5 dBc SFDR at 21 MHz -54 dBc SFDR at 65 MHz Output noise level @ minimum gain 1.2 nV/Hz Maintains 300 output impedance Tx-enable and Tx-disable condition Upper bandwidth: 107 MHz (full gain range) 5 V supply operation Supports SPI interfaces
FUNCTIONAL BLOCK DIAGRAM
BYP
AD8328
VIN+ DIFF OR SINGLE INPUT AMP
VOUT+
VERNIER
VIN-
ATTENUATION CORE 8
POWER AMP
ZOUT DIFF = 300 VOUT-
ZIN (SINGLE) = 800 ZIN (DIFF) = 1.6k
DECODE
8 POWER-DOWN LOGIC
RAMP
DATA LATCH
8 SHIFT REGISTER
APPLICATIONS
DOCSIS and EuroDOCSIS cable modems CATV set-top boxes CATV telephony modems Coaxial and twisted pair line drivers
GND
DATEN SDATA CLK
TXEN
SLEEP
Figure 1.
GENERAL DESCRIPTION
The AD8328 1 is a low cost amplifier designed for coaxial line driving. The features and specifications make the AD8328 ideally suited for MCNS-DOCSIS and EuroDOCSIS applications. The gain of the AD8328 is digitally controlled. An 8-bit serial word determines the desired output gain over a 59 dB range, resulting in gain changes of 1 dB/LSB. The AD8328 accepts a differential or single-ended input signal. The output is specified for driving a 75 load through a 2:1 transformer. Distortion performance of -53 dBc is achieved with an output level up to 60 dBmV at 65 MHz bandwidth over a wide temperature range. This device has a sleep mode function that reduces the quiescent current to 2.6 mA and a full power-down function that reduces power-down current to 20 A. The AD8328 is packaged in a low cost 20-lead LFCSP and a 20-lead QSOP. The AD8328 operates from a single 5 V supply and has an operational temperature range of -40C to +85C.
-50 -52 -54 VOUT = 60dBmV @ MAX GAIN, THIRD HARMONIC
DISTORTION (dBc)
-56 -58 -60 -62 -64 -66 -68 -70 5 15 25 35 45 FREQUENCY (MHz) 55 65
03158-002
VOUT = 60dBmV @ MAX GAIN, SECOND HARMONIC
Figure 2. Worst Harmonic Distortion vs. Frequency
1
Patent pending.
Rev. A
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. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 (c) 2005 Analog Devices, Inc. All rights reserved.
03158-001
AD8328 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Logic Inputs (TTL-/CMOS-Compatible Logic)....................... 4 Timing Requirements .................................................................. 4 Absolute Maximum Ratings............................................................ 6 ESD Caution.................................................................................. 6 Pin Configurations and Function Descriptions ........................... 7 Typical Performance Characteristics ............................................. 8 Applications..................................................................................... 10 General Applications.................................................................. 10 Circuit Description..................................................................... 10 SPI Programming and Gain Adjustment ................................ 10 Input Bias, Impedance, and Termination................................ 10 Output Bias, Impedance, and Termination............................. 10 Power Supply............................................................................... 11 Signal Integrity Layout Considerations................................... 11 Initial Power-Up ......................................................................... 12 RAMP Pin and BYP Pin Features ............................................ 12 Transmit Enable (TXEN) and SLEEP ...................................... 12 Distortion, Adjacent Channel Power, and DOCSIS .............. 12 Noise and DOCSIS..................................................................... 12 Evaluation Board Features and Operation.............................. 12 Differential Signal Source ......................................................... 13 Differential Signal from Single-Ended Source ....................... 13 Single-Ended Source.................................................................. 13 Overshoot on PC Printer Ports ................................................ 13 Installing Visual Basic Control Software................................. 13 Running AD8328 Software ....................................................... 14 Controlling Gain/Attenuation of the AD8328 ....................... 14 Transmit Enable and Sleep Mode............................................. 14 Memory Functions..................................................................... 14 Outline Dimensions ....................................................................... 17 Ordering Guide............................................................................... 18
REVISION HISTORY
10/05--Rev. 0 to Rev. A Updated Format..................................................................Universal Changes to Table 4............................................................................ 6 Updated Outline Dimensions ....................................................... 17 Changes to Ordering Guide .......................................................... 18
11/02--Revision 0: Initial Version
Rev. A | Page 2 of 20
AD8328 SPECIFICATIONS
TA = 25C, VS = 5 V, RL = RIN = 75 , VIN (differential) = 29 dBmV. The AD8328 is characterized using a 2:1 transformer 1 at the device output. Table 1.
Parameter INPUT CHARACTERISTICS Specified AC Voltage Input Resistance Input Capacitance GAIN CONTROL INTERFACE Voltage Gain Range Maximum Gain Minimum Gain Output Step Size Output Step Size Temperature Coefficient OUTPUT CHARACTERISTICS Bandwidth (-3 dB) Bandwidth Roll-Off 1 dB Compression Point 2 Output Noise2 Maximum Gain Minimum Gain Tx Disable Noise Figure2 Maximum Gain Differential Output Impedance OVERALL PERFORMANCE Second-Order Harmonic Distortion 4, 5 Conditions Output = 60 dBmV, max gain Single-ended input Differential input Min Typ 29 800 1600 2 58 30.5 -28.5 0.6 59.0 31.5 -27.5 1.0 0.0005 107 1.2 18.4 3.3 135 1.2 1.1 16.7 75 30% 3 151 1.3 1.2 17.7 60 32.5 -26.5 1.4 Max Unit dBmV pF dB dB dB dB/LSB dB/C MHz dB dBm dBm nV/Hz nV/Hz nV/Hz dB
Gain code = 60 decimal codes Gain code = 1 decimal code TA = -40C to +85C All gain codes (1 to 60 decimal codes) f = 65 MHz Maximum gain, f = 10 MHz, output referred Minimum gain, f = 10 MHz, input referred f = 10 MHz f = 10 MHz f = 10 MHz f = 10 MHz Tx enable and Tx disable
17.9 2.2
Third-Order Harmonic Distortion4, 5 ACPR2, 6 Isolation (Tx Disable)2 POWER CONTROL Tx Enable Settling Time Tx Disable Settling Time Output Switching Transients2 Output Settling Due to Gain Change Due to Input Step Change POWER SUPPLY Operating Range Quiescent Current
f = 33 MHz, VOUT = 60 dBmV @ maximum gain f = 65 MHz, VOUT = 60 dBmV @ maximum gain f = 21 MHz, VOUT = 60 dBmV @ maximum gain f = 65 MHz, VOUT = 60 dBmV @ maximum gain Maximum gain, f = 65 MHz Maximum gain, VIN = 0 Maximum gain, VIN = 0 Equivalent output = 31 dBmV Equivalent output = 61 dBmV Minimum to maximum gain Maximum gain, VIN = 29 dBmV 4.75 98 18 1 1 -40
-67 -61 -57.5 -54 -58 -85 2.5 3.8 2.5 16 60 30 5 120 26 2.6 20
-56 -55 -56 -52.5 -56 -81
dBc dBc dBc dBc dBc dB s s mV p-p mV p-p ns ns
6 54
Maximum gain Minimum gain Tx disable (TXEN = 0) SLEEP mode (power-down)
5.25 140 34 3.5 100 +85
V mA mA mA A C
OPERATING TEMPERATURE RANGE
Rev. A | Page 3 of 20
AD8328
1 2
TOKO 458 PT-1087 used for above specifications. Typical insertion loss of 0.3 dB @ 10 MHz. Guaranteed by design and characterization to 4 sigma for TA = 25C. 3 Measured through a 2:1 transformer. 4 Specification is worst case over all gain codes. 5 Guaranteed by design and characterization to 3 sigma for TA = 25C. 6 VIN = 29 dBmV, QPSK modulation, 160 kSPS symbol rate.
LOGIC INPUTS (TTL-/CMOS-COMPATIBLE LOGIC)
DATEN, CLK, SDATA, TXEN, SLEEP, VCC = 5 V; full temperature range. Table 2.
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 Max 5.0 0.8 20 -100 190 -30 190 -30 Unit V V nA nA A A A A
TIMING REQUIREMENTS
Full temperature range, VCC = 5 V, tR = tF = 4 ns, fCLK = 8 MHz, unless otherwise noted. Table 3.
Parameter Clock Pulse Width (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) Min 16.0 32.0 5.0 15.0 5.0 3.0 Typ Max Unit ns ns ns ns ns ns ns
10
Rev. A | Page 4 of 20
AD8328
t DS
SDATA
VALID DATA-WORD G1 MSB. . . .LSB VALID DATA-WORD G2
tC t WH
CLK
t ES
DATEN
t EH
8 CLOCK CYCLES
GAIN TRANSFER (G1)
GAIN TRANSFER (G2)
t OFF
TXEN
t GS t ON
03158-003
ANALOG OUTPUT SIGNAL AMPLITUDE (p-p)
Figure 3. Serial Interface Timing
VALID DATA BIT
SDATA
MSB
MSB-1
MSB-2
t DS
t DH
Figure 4. SDATA Timing
Rev. A | Page 5 of 20
03158-004
CLK
AD8328 ABSOLUTE MAXIMUM RATINGS
Table 4.
Parameter Supply Voltage VCC Input Voltage VIN+, VIN- DATEN, SDATA, CLK, SLEEP, TXEN Internal Power Dissipation QSOP (JA = 83.2C/W) 1 LFCSP (JA = 30.4C/W) 2 Operating Temperature Range Storage Temperature Range Lead Temperature, Soldering 60 sec
1 2
Rating 6V 1.5 V p-p -0.8 V to +5.5 V 700 mW 700 mW -40C to +85C -65C to +150C 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.
Thermal resistance measured on SEMI standard 4-layer board. Thermal resistance measured on SEMI standard 4-layer board, paddle soldered to board.
ESD 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 this product 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.
Rev. A | Page 6 of 20
AD8328 PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
GND VCC GND
GND 1 VCC
2
20 19 18
GND VCC TXEN RAMP
GND 1 GND 2 VIN+ 3 VIN- 4 GND 5
20 19 18 17 16 15 RAMP
GND 3 GND 4 VIN+ VIN- DATEN SDATA
5
16 VOUT+ TOP VIEW 6 (Not to Scale) 15 V OUT- 14 13 12 11
AD8328
17
VCC
TXEN
AD8328
TOP VIEW (Not to Scale)
14 VOUT+ 13 VOUT- 12 BYP 11 NC
GND 7
8 9
BYP NC SLEEP
03158-005
6
DATEN
7
SDATA
8
CLK
9
GND
10
SLEEP
03158-006
CLK 10
GND
NC = NO CONNECT
Figure 5. 20-Lead QSOP Pin Configuration
Figure 6. 20-Lead LFCSP Pin Configuration
Table 5. 20-Lead QSOP and 20-Lead LFCSP Pin Function Descriptions
Pin No. 20-Lead QSOP 1, 3, 4, 7, 11, 20 2, 19 5 6 8 Pin No. 20-Lead LFCSP 1, 2, 5, 9, 18, 19 17, 20 3 4 6
Mnemonic GND VCC VIN+ VIN- DATEN
Description Common External Ground Reference. Common Positive External Supply Voltage. A 0.1 F capacitor must decouple each pin. 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. Data Enable Low Input. This port controls the 8-bit parallel data latch and shift register. A Logic 0-to-Logic 1 transition transfers the latched data to the attenuator core (updates the gain) and simultaneously inhibits serial data transfer into the register. A Logic 1-to-Logic 0 transition inhibits the data latch (holds the previous gain state) and simultaneously enables the register for serial data load. Serial Data Input. This digital input allows an 8-bit serial (gain) word to be loaded into the internal register with the most significant bit (MSB) first. Clock Input. The clock port controls the serial attenuator data transfer rate to the 8-bit master-slave register. A Logic 0-to-Logic 1 transition latches the data bit, and a Logic 1-to-Logic 0 transfers the data bit to the slave. This requires the input serial data-word to be valid at or before this clock transition. Low Power Sleep Mode. In the sleep mode, the AD8328's supply current is reduced to 20 A. A Logic 0 powers down the part (high ZOUT state), and a Logic 1 powers up the part. No Connect. Internal Bypass. This pin must be externally ac-coupled (0.1 F capacitor). Negative Output Signal Positive Output Signal External RAMP Capacitor (Optional) Logic 0 Disables Forward Transmission. Logic 1 enables forward transmission.
9 10
7 8
SDATA CLK
12 13 14 15 16 17 18
10 11 12 13 14 15 16
SLEEP NC BYP VOUT- VOUT+ RAMP TXEN
Rev. A | Page 7 of 20
AD8328 TYPICAL PERFORMANCE CHARACTERISTICS
-55
-50
VOUT = 61dBmV @ MAX GAIN
-60
DISTORTION (dBc)
VOUT = 60dBmV @ MAX GAIN
-65
DISTORTION (dBc)
VOUT = 61dBmV @ MAX GAIN
VOUT = 60dBmV @ MAX GAIN
-55
-60
VOUT = 59dBmV @ MAX GAIN
-70
03158-007
VOUT = 59dBmV @ MAX GAIN
-65
03158-010
-75
5 15 25 35 45 FREQUENCY (MHz) 55 65
-70
5
15
25 35 45 FREQUENCY (MHz)
55
65
Figure 7. Second-Order Harmonic Distortion vs. Frequency for Various Output Powers
-50
VOUT = 60dBmV @ MAX GAIN
-50
Figure 10. Third-Order Harmonic Distortion vs. Frequency for Various Output Powers
VOUT = 60dBmV @ MAX GAIN TA = +85C
-55
DISTORTION (dBc)
TA = +25C
TA = -40C
DISTORTION (dBc)
-55
-60
TA = +25C
-65
TA = +85C
03158-008
TA = -40C
-60
-70
-75
5
15
25
35
45
55
65
-65
5
15
FREQUENCY (MHz)
25 35 45 FREQUENCY (MHz)
55
65
Figure 8. Second-Order Harmonic Distortion vs. Frequency vs. Temperature
10
0
CH PWR ACP 60dBmV -58.2dB
Figure 11. Third-Order Harmonic Distortion vs. Frequency vs. Temperature
60 50 40 30
VOUT = 57dBmV/TONE @ MAX GAIN
-10 -20
VOUT (dBmV)
POUT (dBm)
-30 -40 -50 -60 -70 -80 -90
c11 c11 cu1 C0 C0 cu1
03158-009
20 10 0
-10 -20 -30 -40 41.6
03158-012
75kHz/DIV
SPAN 750kHz
41.7
41.8
Figure 9. Adjacent Channel Power
41.9 42.0 42.1 42.2 FREQUENCY (MHz)
42.3
42.4
42.5
Figure 12. Two-Tone Intermodulation Distortion
Rev. A | Page 8 of 20
03158-011
AD8328
40 30 20 10 DEC60 DEC54
ISOLATION (dB)
0 -10 -20 -30 -40 -50 -60 -70 -80
03158-013
TXEN = 0 VIN = 29dBmV
GAIN (dB)
DEC48
0
DEC42
DEC36
-10 DEC30
DEC24
-20 -30
DEC18 DEC12
DEC 1 TO DEC 6 1 10 100 FREQUENCY (MHz)
MAX GAIN MIN GAIN
03158-016
-90 -100
-40 0.1
1000
1
10
100
1000
FREQUENCY (MHz)
Figure 13. AC Response
1.4 f = 10MHz 1.2
Figure 16. Isolation in Transmit Disable Mode vs. Frequency
1.6 1.2 0.8
OUTPUT STEP SIZE (dB)
GAIN ERROR (dB)
0.4 0 -0.4
f = 10MHz f = 5MHz f = 42MHz
1.0
0.8
03158-014
-0.8
03158-017
-1.2 -1.6
f = 65MHz
0 6 12 18 24 30 36 42 48 54 60
0.6
0
6
12
18
24
30
36
42
48
54
60
GAIN CONTROL (Decimal Code)
GAIN CONTROL (Decimal Code)
Figure 14. Output Step Size vs. Gain Control
140
OUTPUT REFERRED VOLTAGE NOISE (nV/Hz)
Figure 17. Gain Error vs. Gain Control
130 120
QUIESCENT SUPPLY CURRENT (mA)
f = 10MHz
TXEN = 1
120 100 80 60 40 20 0
0 6 12 18 24 30 36 42 48 GAIN CONTROL (Decimal Code) 54 60
110 100 90 80 70 60 50 40 30 20 0 10 20 30 40 GAIN CONTROL (Decimal Code) 50 60
03158-018
Figure 15. Output Referred Voltage Noise vs. Gain Control
03158-015
Figure 18. Supply Current vs. Gain Control
Rev. A | Page 9 of 20
AD8328 APPLICATIONS
GENERAL APPLICATIONS
The AD8328 is primarily intended for use as the power amplifier (PA) in Data Over Cable Service Interface Specification (DOCSIS)-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 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 head-end, the upstream PA must be capable of varying the output power by applying gain or attenuation. The ability to vary the output power of the AD8328 ensures that the signal from the cable modem has the proper level once it arrives at the head-end. The upstream signal path commonly includes a diplexer and cable splitters. The AD8328 has been designed to overcome losses associated with these passive components in the upstream cable path.
SPI PROGRAMMING AND GAIN ADJUSTMENT
The AD8328 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 on the rising edge of the CLK pulses, MSB first. 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 AD8328 is shown in Figure 3 and Figure 4. The programmable gain range of the AD8328 is -28 dB to +31 dB with steps of 1 dB per least significant bit (LSB). This provides a total gain range of 59 dB. The AD8328 was characterized with a differential signal on the input and a TOKO 458PT-1087 2:1 transformer on the output. The AD8328 incorporates supply current scaling with gain code, as shown in Figure 18. This allows reduced power consumption when operating in lower gain codes.
CIRCUIT DESCRIPTION
The AD8328 is composed of three analog functions in the power-up 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 out of phase and of equal amplitude. A vernier is used in the input stage for controlling the fine 1 dB gain steps. This stage then drives a DAC, which provides the bulk of the AD8328's attenuation. 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 output stage maintains 300 differential output impedance, which maintains proper match to 75 when used with a 2:1 balun transformer.
5V
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 as shown in Figure 20. The differential input impedance of the AD8328 is approximately 1.6 k, while the single-ended input is 800 . The high input impedance of the AD8328 allows flexibility in termination and properly matching filter networks. The AD8328 exhibits optimum performance when driven with a pure differential signal.
OUTPUT BIAS, IMPEDANCE, AND TERMINATION
The output stage of the AD8328 requires a bias of 5 V. The 5 V power supply should be connected to the center tap of the output transformer. In addition, the VCC applied to the center tap of the transformer should be decoupled as seen in Figure 20.
VCC VIN+ VOUT+
AD8328
1V 2 IN 1V 2 IN
VIN- BYP GND VOUT-
RL
Figure 19. Characterization Circuit
Rev. A | Page 10 of 20
03158-019
AD8328
VCC
10F
1
AD8328
QSOP
0.1F
VIN+
ZIN = 150
165
0.1F
VIN-
DATEN SDATA CLK TXEN SLEEP
1k 1k 1k
GND 2 VCC 3 GND 4 GND 5 VIN+ 6 VIN- 7 GND 8 DATEN 9 SDATA 10 CLK
20 GND 19 VCC 18 TXEN 17 RAMP 16 VOUT+ 15 VOUT- 14 BYP 13 NC 0.1F 12 SLEEP 11 GND
0.1F
TO DIPLEXER ZIN = 75
TOKO 458PT-1087
0.1F
1k
Figure 20. Typical Application Circuit
Table 6. Adjacent Channel Power
Channel Symbol Rate (kSym/s) 160 320 640 1280 2560 5120 Adjacent Channel Symbol Rate (kSym/s) 160 320 640 1280 -58 -60 -63 -66 -58 -59 -60 -64 -60 -58 -59 -61 -62 -60 -59 -60 -64 -62 -60 -59 -66 -65 -62 -61 2560 -66 -66 -64 -61 -60 -59 5120 -64 -65 -65 -63 -61 -60
The output impedance of the AD8328 is 300 , regardless of whether the amplifier is in transmit enable or transmit disable mode. This, when combined with a 2:1 voltage ratio (4:1 impedance ratio) transformer, 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. The AD8328 evaluation board provides a convenient means to implement a matching attenuator. Soldering a 43.3 resistor in the R15 placeholder and an 86.6 resistor in the R16 placeholder allows testing on a 50 system. When using a matching attenuator, it should be noted that there is a 5.7 dB of power loss (7.5 dB voltage) through the network.
AD8328 and the output transformer. All AD8328 ground pins must be connected to the ground plane to ensure proper grounding of all internal nodes.
SIGNAL INTEGRITY LAYOUT CONSIDERATIONS
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. Keeping the traces short minimizes parasitic capacitance and inductance. This is most critical between the outputs of the AD8328 and the 2:1 output transformer. It is also critical that all differential signal paths be symmetrical in length and width. In addition, the input and output traces should be adequately spaced to minimize coupling (crosstalk) through the board. Following these guidelines optimizes the overall performance of the AD8328 in all applications.
POWER SUPPLY
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 AD8328. In addition to the 10 F capacitor, each VCC pin should be individually decoupled to ground with ceramic chip capacitors located close to the pins. The bypass pin, BYP, should also be decoupled. 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
Rev. A | Page 11 of 20
03158-020
1k
AD8328
INITIAL POWER-UP
When the supply voltage is first applied to the AD8328, the gain of the amplifier is initially set to Gain Code 1. Since power is first applied to the amplifier, the TXEN pin should be held low (Logic 0) to prevent forward signal transmission. After power is 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. 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) are 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 2.0, Section 6.2.21.1.1 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." Figure 9 shows the measured ACP for a 60 dBmV QPSK signal taken at the output of the AD8328 evaluation board. The transmit channel width and adjacent channel width in Figure 9 correspond to the symbol rates of 160 kSym/s. Table 6 shows the ACP results for the AD8328 driving a QPSK 60 dBmV signal for all conditions in DOCSIS Table 6-9, Adjacent Channel Spurious Emissions.
RAMP PIN AND BYP PIN FEATURES
The RAMP pin is used to control the length of the burst on and off transients. By default, leaving the RAMP pin unconnected results in a transient that is fully compliant with DOCSIS 2.0 Section 6.2.21.2, Spurious Emissions During Burst On/Off Transients. DOCSIS requires that all between-burst transients must be dissipated no faster than 2 s; and adding capacitance to the RAMP pin adds more time to the transient. The BYP pin is used to decouple the output stage at midsupply. Typically, for normal DOCSIS operation, the BYP pin should be decoupled to ground with a 0.1 F capacitor. However, in applications that require transient on/off times faster than 2 s, smaller capacitors can be used, but it should be noted that the BYP pin should always be decoupled to ground.
NOISE AND DOCSIS
At minimum gain, the AD8328 output noise spectral density is 1.2 nV/Hz measured at 10 MHz. DOCSIS Table 6-10, Spurious Emissions in 5 MHz to 42 MHz, specifies the output noise for various symbol rates. The calculated noise power in dBmV for 160 kSym/s is
2 20 x log 1.2 nV x 160 kHz + 60 = -66.4 dBmV Hz
(1)
TRANSMIT ENABLE (TXEN) AND SLEEP
The asynchronous TXEN pin is used to place the AD8328 into between-burst mode. In this reduced current state, the output impedance of 75 is maintained. Applying Logic 0 to the TXEN pin deactivates the on-chip amplifier, providing a 97.8% reduction in consumed power. For 5 V operation, the supply current is typically reduced from 120 mA to 2.6 mA. In this mode of operation, between-burst noise is minimized and high input to output isolation is achieved. In addition to the TXEN pin, the AD8328 also incorporates an asynchronous SLEEP pin, which can be used to further reduce the supply current to approximately 20 A. Applying Logic 0 to the SLEEP pin places the amplifier into SLEEP mode. Transitioning into or out of SLEEP mode can result in a transient voltage at the output of the amplifier.
Comparing the computed noise power of -66.4 dBmV to the +8 dBmV signal yields -74.4 dBc, which meets the required level set forth in DOCSIS Table 6-10. As the AD8328 gain is increased above this minimum value, the output signal increases at a faster rate than the noise, resulting in a signalto-noise ratio that improves with gain. In transmit disable mode, the output noise spectral density is 1.1 nV/Hz, which results in -67 dBmV when computed over 160 kSym/s. The noise power was measured directly at the output of the AD8328AR-EVAL board.
EVALUATION BOARD FEATURES AND OPERATION
The AD8328 evaluation board and control software can be used to control the AD8328 upstream cable driver via the parallel port of a PC. A standard printer cable connected to the parallel port of the PC is used to feed all the necessary data to the AD8328 using the Windows(R)-based control software. This package provides a means of controlling the gain and the power mode of the AD8328. With this evaluation kit, the AD8328 can be evaluated in either a single-ended or differential input configuration. See Figure 26 for a schematic of the evaluation board.
DISTORTION, ADJACENT CHANNEL POWER, AND DOCSIS
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. This added power 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 AD8328 was characterized with a differential input signal. Figure 7 and Figure 10 show the AD8328 second and third harmonic distortion performance vs. the fundamental frequency for
Rev. A | Page 12 of 20
AD8328
DIFFERENTIAL SIGNAL SOURCE
Typical applications for the AD8328 use a differential input signal from a modulator or a DAC. See Table 7 for common values of R4, or calculate other input configurations using Equation 2. This circuit configuration will give optimal distortion results due to the symmetric input signals. Note that this configuration was used to characterize the AD8328.
R4 = Z IN x 1.6 k 1.6 k - Z IN
VIN+ ZIN VIN- R4
requires the removal of R2 and R3 to be shorted with R4 open, as well as the addition of 82.5 at R1 and 39.2 at R17 for 75 termination. Table 7 shows the correct values for R11 and R12 for some common input configurations. Other input impedance configurations can be accommodated using Equation 4 and Equation 5.
R1 =
(2)
Z IN x 800 800 - Z IN
(4)
R17 =
AD8328
03158-021
Z IN x R1 R1 + Z IN
VIN+
(5)
R1
ZIN
AD8328
R17
03158-023
Figure 21. Differential Circuit
DIFFERENTIAL SIGNAL FROM SINGLE-ENDED SOURCE
The default configuration of the evaluation board implements a differential signal drive from a single-ended signal source. This configuration uses a 1:1 balun transformer to approximate a differential signal. Because of the nonideal nature of real transformers, the differential signal is not purely equal and opposite in amplitude. Although this circuit slightly sacrifices even-order harmonic distortion due to asymmetry, it does provide a convenient way to evaluate the AD8328 with a singleended source. The AD8328 evaluation board is populated with a TOKO 617DB-A0070 1:1 for this purpose (T1). Table 7 provides typical R4 values for common input configurations. Other input impedances can be calculated using Equation 3. See Figure 26 for a schematic of the evaluation board. To use the transformer for converting a single-ended source into a differential signal, the input signal must be applied to VIN+.
Figure 23. Single-Ended Circuit
Table 7. Common Matching Resistors
ZIN () 50 75 100 150 ZIN () 50 75 Differential Input Termination R2/R3 R4 () R1/R17 Open 51.1 Open/Open Open 78.7 Open/Open Open 107.0 Open/Open Open 165.0 Open/Open Single-Ended Input Termination R2 ()/R3 () R4 () R1 ()/R17 () 0/0 Open 53.6/25.5 0/0 Open 82.5/39.2
OVERSHOOT ON PC PRINTER PORTS
The data lines on some PC parallel printer ports have excessive overshoot that can cause communication problems when presented to the CLK pin of the AD8328. The evaluation board was designed to accommodate a series resistor and shunt capacitor (R2 and C5 in Figure 26) to filter the CLK signal if required.
R4 =
Z IN x 1.6 k 1.6 k - Z IN
VIN+
03158-022
(3)
INSTALLING VISUAL BASIC CONTROL SOFTWARE
R4
ZIN
AD8328
Figure 22. Single-to-Differential Circuit
SINGLE-ENDED SOURCE
Although the AD8328 was designed to have optimal DOCSIS performance when used with a differential input signal, the AD8328 can also be used as a single-ended receiver, or an IF digitally controlled amplifier. However, as with the singleended-to-differential configuration previously noted, evenorder harmonic distortion is slightly degraded. When operating the AD8328 in a single-ended input mode, VIN+ and VIN- should be terminated as shown in Figure 23. On the AD8328 evaluation boards, this termination method
Install the CabDrive_28 software by running the setup.exe file on Disk One of the AD8328 evaluation software. Follow the onscreen directions and insert Disk Two when prompted. Choose the installation directory and then select the icon in the upper left to complete the installation.
Rev. A | Page 13 of 20
AD8328
RUNNING AD8328 SOFTWARE
To load the control software, go to Start, Programs, CABDRIVE_28 or select the AD8328.exe file from the installed directory. Once loaded, select the proper parallel port to communicate with the AD8328 (see Figure 24).
TRANSMIT ENABLE AND SLEEP MODE
The Transmit Enable and Transmit Disable buttons select the mode of operation of the AD8328 by asserting logic levels on the asynchronous TXEN pin. The Transmit Disable button applies Logic 0 to the TXEN pin, disabling forward transmission. The Transmit Enable button applies Logic 1 to the TXEN pin, enabling the AD8328 for forward transmission. Checking the Enable SLEEP Mode box applies Logic 0 to the asynchronous SLEEP pin, setting the AD8328 for SLEEP mode.
MEMORY FUNCTIONS
The Memory section of the software provides a way to alternate between two gain settings. The XM1 button stores the current value of the GAIN SLIDER into memory, while the RM1 button recalls the stored value, returning the gain SLIDER to the stored level. The same applies to the XM2 and RM2 buttons.
Figure 24. Parallel Port Selection
CONTROLLING GAIN/ATTENUATION OF THE AD8328
The SLIDER controls the gain/attenuation of the AD8328, which is displayed in dB and in V/V. The gain scales 1 dB per LSB. The gain code from the position of the SLIDER is displayed in decimal, binary, and hexadecimal (see Figure 25).
Figure 25. Control Software Interface
Rev. A | Page 14 of 20
03158-025
03158-024
AD8328
VIN+_A R1 R2 T1 TOKO 617DB-A0070 C1A 0.1F TP9 R4 78.7 C2A 0.1F
1 2 3
GND VCC GND GND VIN+ VIN- GND DATEN SDATA CLK QSOP
GND VCC TXEN RAMP VOUT+ VOUT- BYP NC SLEEP GND
20 19 18 17 16 15 14 13 12 11
C9 0.1F
C8 10F
VCC
VIN-_A R17 R5 1k TP1
R3
C10 0.1F
4
P1 2
R6 0
5 6
C11 TOKO R15 458PT-1087 0 C12 0.1F VCC1 1 2 3 4 6 CABLE_OA R16
C3
7 8
P1 3
R7 1k
TP2
R8 0
9 10
C4 TP3
AD8328
C13 0.1F
P1 5
R9 1k
R10 0 TP10 TP11
C5 TP4
P1 6
R11 1k C6
R12 0 TP_AGND1 AGND1
TP12
TP_VCC1 VCC1
P1 7 P1 16
R13 1k C7
TP5
P1 19 P1 20 P1 21 P1 22 P1 23 P1 24 P1 25 P1 26 P1 27 P1 28 P1 29 P1 30 P1 33
R14 0
03158-026
Figure 26. AD8328 Evaluation Board Schematic
Rev. A | Page 15 of 20
AD8328
03158-027
Figure 27. Primary Side
Figure 30. Internal Ground Plane
03158-028
Figure 28. Component Side Silkscreen
Figure 31. Secondary Side
03158-029
Figure 29. Internal Power Plane
Figure 32. Secondary Side Silkscreen
Rev. A | Page 16 of 20
03158-032
03158-031
03158-030
AD8328 OUTLINE DIMENSIONS
4.00 BSC SQ 0.60 MAX PIN 1 INDICATOR TOP VIEW 3.75 BCS SQ 0.75 0.55 0.35 0.05 MAX 0.02 NOM COPLANARITY 0.08
11 10 6 5
0.60 MAX
16 15
PIN 1 INDICATOR
20 1
2.25 2.10 SQ 1.95 0.25 MIN 0.30 0.23 0.18
1.00 0.85 0.80 SEATING PLANE
12 MAX
0.80 MAX 0.65 TYP
0.50 BSC
0.20 REF
COMPLIANT TO JEDEC STANDARDS MO-220-VGGD-1
Figure 33. 20-Lead Frame Chip Scale Package [LFCSP_VQ] 4 mm x 4 mm Body, Very Thin Quad (CP-20-1) Dimensions shown in millimeters
0.345 0.341 0.337
20
11
0.158 0.154 0.150
1
10
0.244 0.236 0.228
PIN 1
0.065 0.049
0.069 0.053 8 0
0.010 0.004 COPLANARITY 0.004
0.025 BSC
0.012 0.008
SEATING PLANE
0.010 0.006
0.050 0.016
COMPLIANT TO JEDEC STANDARDS MO-137-AD
Figure 34. 20-Lead Shrink Small Outline Package [QSOP] (RQ-20) Dimensions shown in inches
Rev. A | Page 17 of 20
AD8328
ORDERING GUIDE
Model AD8328ARQ AD8328ARQ-REEL AD8328ARQZ 1 AD8328ARQZ-REEL1 AD8328ACP AD8328ACP-REEL AD8328ACP-REEL7 AD8328ACPZ1 AD8328ACPZ-REEL1 AD8328ACPZ-REEL71 AD8328ACP-EVAL AD8328ARQ-EVAL
1
Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Package Description 20-Lead QSOP 20-Lead QSOP 20-Lead QSOP 20-Lead QSOP 20-Lead LFCSP_VQ 20-Lead LFCSP_VQ 20-Lead LFCSP_VQ 20-Lead LFCSP_VQ 20-Lead LFCSP_VQ 20-Lead LFCSP_VQ Evaluation Board Evaluation Board
Package Option RQ-20 RQ-20 RQ-20 RQ-20 CP-20-1 CP-20-1 CP-20-1 CP-20-1 CP-20-1 CP-20-1
Z = Pb-free part.
Rev. A | Page 18 of 20
AD8328 NOTES
Rev. A | Page 19 of 20
AD8328 NOTES
(c) 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C03158-0-10/05(A)
Rev. A | Page 20 of 20

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