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FEATURES Supports DOCSIS Standard for Reverse Path Transmission Gain Programmable in 6 dB Steps Over a 42 dB Range Low Distortion at 60 dBmV Output -58 dBc SFDR at 21 MHz -56 dBc SFDR at 42 MHz Output Noise Level -46 dBmV in 160 kHz Bandwidth Maintains 75 Output Impedance Power-Up and Power-Down Condition 180 MHz Bandwidth 5 V Supply Operation Supports SPI Interfaces APPLICATIONS Gain Programmable Line Driver DOCSIS-Compliant Data Modems Interactive Set-Top Boxes PC Plug-in Modems General-Purpose Digitally Controlled Variable Gain Block
5 V CATV Line Driver Coarse Step Output Power Control AD8322
FUNCTIONAL BLOCK DIAGRAM
VCC (7 PINS) R1
AD8322
VOUT+ BUFFER ATTENUATION CORE 8 DECODE 8 DATA LATCH 8 SHIFT REGISTER POWER AMP ZOUT DIFF = 75 POWER-DOWN LOGIC VOUT-
VIN+ VIN-
DIFF OR SINGLE INPUT AMP R2 ZIN (SINGLE) = 210 ZIN (DIFF) = 235
DATEN
DATA CLK
GND (12 PINS)
PD
GENERAL DESCRIPTION
-55 fO = 42MHz VO = 60dBmV @ MAX GAIN -60
DISTORTION - dBc
The AD8322 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 42.14 dB range, with gain steps of 6.02 dB/major carry. The AD8322 comprises a digitally controlled variable attenuator of 0 dB to -42.14 dB, which is preceded by a low-noise, fixed-gain buffer and is followed by a low-distortion, high-power amplifier. The AD8322 accepts a differential or single-ended input signal. The output is specified for driving a 75 load, such as coaxial cable. Distortion performance of -58 dBc is achieved with an output level up to 60 dBmV at 21 MHz bandwidth. A key performance and cost advantage of the AD8322 results from the ability to maintain a constant 75 output impedance during power-up and powerdown conditions. This eliminates the need for external 75 termination resulting in twice the effective output voltage when compared to a standard operational amplifier. The AD8322 is packaged in a low-cost 28-lead TSSOP, operates from a single 5 V supply, and has an operational temperature range of -40C to +85C.
HD3 -65
HD2 -70
-75
1
2
4
8 16 32 GAIN CODE - Decimal
64
128
Figure 1. Harmonic Distortion vs. Gain Control
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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 which 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 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 2000
AD8322-SPECIFICATIONS a 1:1 transformer with insertion loss of 0.5 dB @ 10 MHz unless otherwise noted)
1
(TA = 25 C, VS = 5 V, RL = RIN = 75
, VIN = 92 mV p-p differential, VOUT measured through
Typ 92 11.8 210 235 2 Max Unit mV p-p dB pF 43.2 31.5 -10.64 dB dB dB dB/Major Carry MHz dB dB dBmV in 160 kHz BW dBmV in 160 kHz BW dBmV in 160 kHz BW dBm dBc dBc dBc dBc dBc 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
Conditions POUT = 60 dBmV, Max Gain Max Gain, f = 10 MHz Single-Ended Input Differential Input
Min
Gain Code = 1xxxxxxx Gain Code = 00000001
41.0 42.14 27.5 29.5 -14.64 -12.64 6.02 180 0.25 0.05 -32 -46 -68 19 75 20% -64 -60 -58 -57 -56 -52 -67 -64 -61 -58 -56 -53 0.2 60 30 -24
1 dB Compression Point Differential Output Impedance OVERALL PERFORMANCE Second Order Harmonic Distortion2
All Gain Codes f = 65 MHz f = 65 MHz Max Gain, f = 10 MHz Min Gain, f = 10 MHz Power-Down Mode, f = 10 MHz Max Gain, f = 10 MHz Power-Up and Power-Down f = 5 MHz, POUT = 60 dBmV @ Max Gain f = 14 MHz, POUT = 60 dBmV @ Max Gain f = 21 MHz, POUT = 60 dBmV @ Max Gain f = 32 MHz, POUT = 60 dBmV @ Max Gain f = 42 MHz, POUT = 60 dBmV @ Max Gain f = 65 MHz, POUT = 60 dBmV @ Max Gain f = 5 MHz, POUT = 60 dBmV @ Max Gain f = 14 MHz, POUT = 60 dBmV @ Max Gain f = 21 MHz, POUT = 60 dBmV @ Max Gain f = 32 MHz, POUT = 60 dBmV @ Max Gain f = 42 MHz, POUT = 60 dBmV @ Max Gain f = 65 MHz, POUT = 60 dBmV @ Max Gain f = 10 MHz, Code to Code Min to Max Gain Max Gain, VIN = 0 V to 0.09 V p-p Max Gain, Power-Down, f = 42 MHz, VIN = 0.09 V p-p Max Gain, VIN = 0 Max Gain, VIN = 0 Equivalent POUT = 17.6 to 35.67 dBmV Equivalent POUT = 60 dBmV 4.75 100 44 -40
Third Order Harmonic Distortion
Gain Linearity Error Output Settling to 1 mV Due to Gain Change Due to Input Change Signal Feedthrough POWER CONTROL Power-Up Settling Time to 1 mV Power-Down Settling Time to 1 mV Between Burst Transients3 POWER SUPPLY Operating Range Quiescent Current OPERATING TEMPERATURE RANGE
300 40 3 16 5 113 54 5.25 126 60 +85
ns ns mV p-p mV p-p V mA mA C
Power-Up Mode Power-Down Mode
NOTES 1 TOKO # 617 DB-A0070 used for above specifications. MACOM ETC-1-IT-15 can be substituted. 2 All distortion measurements taken with differential input signal and represent worst distortion across all gain codes. 3 Between burst transients measured at the output of PULSE B5008 42 MHz diplexer. Specifications subject to change without notice.
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AD8322 LOGIC INPUTS (TTL/CMOS Compatible Logic)
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) PD Logic "0" Current (VINL = 0 V) PD
(DATEN, CLK, SDATA, PD, VCC = 5 V: Full Temperature Range)
Min 2.1 0 0 -600 50 -250 Typ Max 5.0 0.8 20 -100 190 -30 Unit V V nA nA A A
TIMING REQUIREMENTS (Full Temperature Range, V
Parameter 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)
CC
= 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
Table I. Gain vs. Gain Code
Typ
Max
Unit ns ns ns ns ns ns ns
TDS SDATA
VALID DATA WORD G1 MSB. . . .LSB VALID DATA WORD G2
TC TWH CLK TES DATEN TEH
Decimal Gain Code 1 2 4 8 16 32 64 128
8-Bit SPI Data Word MSB LSB 00000001 00000010 00000100 00001000 00010000 00100000 01000000 1xxxxxxx
Nominal Gain (dB) -12.64 -6.62 -0.60 5.42 11.44 17.46 23.48 29.50
8 CLOCK CYCLES
GAIN TRANSFER (G1) TOFF PD TGS
GAIN TRANSFER (G2)
0 = low, 1 = high, x = don't care.
TON
ANALOG OUTPUT SIGNAL AMPLITUDE (p-p) PEDESTAL
Figure 2. Serial Interface Timing
VALID DATA BIT
SDATA MSB
MSB-1
MSB-2
TDS
TDH
CLK
Figure 3. SDATA Timing
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AD8322
ABSOLUTE MAXIMUM RATINGS* PIN CONFIGURATION
SDATA CLK DATEN GND BYP VCC PD VCC VCC GND VCC VIN- VIN+ GND VCC
Supply Voltage +VS Pins 6, 8, 9, 20, 21, 23, 27 . . . . . . . . . . . . . . . . . . . . . . . 6 V Input Voltages Pins 25, 26 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5 V Pins 1, 2, 3, 7 . . . . . . . . . . . . . . . . . . . . . . . -0.8 V to +5.5 V Internal Power Dissipation TSSOP (RU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.90 W 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.
1 2 3 4 5 6 7 8 9
28 27 26 25 24
AD8322
23 22
GND TOP VIEW (Not to Scale) 21 VCC
20 19 18 17 16 15
VCC OUT+ GND GND GND GND
OUT- 10 GND 11 GND 12 GND 13 GND 14
ORDERING GUIDE
Model AD8322ARU AD8322ARU-REEL AD8322-EVAL
Temperature Range -40C to +85C -40C to +85C
Package Description 28-Lead TSSOP 28-Lead TSSOP Evaluation Board
JA
Package Option RU-28 RU-28
67.7C/W* 67.7C/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 AD8322 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. PIN FUNCTION DESCRIPTIONS Pin No. 1 2 Mnemonic SDATA CLK Description
WARNING!
ESD SENSITIVE DEVICE
3
DATEN
4, 11, 12, 13, 14, 15, 16, 17, 18, 22, 24, 28 5 6, 8, 9, 20, 21, 23, 27 7 10 19 25 26
GND
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 master-slave 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. 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. Common External Ground Reference.
BYP VCC PD OUT- OUT+ VIN+ VIN-
Internal Bypass. This pin must be externally ac-decoupled (0.1 F capacitor). Common Positive External Supply Voltage. A 0.1 F capacitor must decouple each pin. Logic "0" powers down the part. Logic "1" powers up the part. Negative Output Signal. Positive Output Signal. Noninverting Input. DC-biased to approximately V CC/2. Refer to Applications section for proper termination. Inverting Input. DC-biased to approximately V CC/2. Refer to Applications section for proper termination.
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Typical Performance Characteristics- AD8322
5V
10 F 0.1 F 75 +1/2 VIN 432 75 VIN- -1/2 VIN 0.1 F BYP 0.1 F GND 0.1 F VIN+ VCC OUT+
0.1 F + CL OUT- 0.1 F 1:1 TOKO 617DB-A0070 75 VO -
AD8322
DEVICE UNDER TEST
TPC 1. Test Circuit
0.15 0.10 0.05 GAIN ERROR - dB f = 10MHz
32 PO = 60dBmV @ MAX GAIN CL = 0pF
30 0.00 -0.05 -0.10 -0.15 -0.20 26 -0.25 -0.30 -0.35 1 2 4 8 16 32 GAIN CONTROL - Decimal 64 128 24 1 10 FREQUENCY - MHz f = 65MHz f = 5MHz f = 42MHz
GAIN - dB
28 CL = 10pF CL = 20pF
CL = 50pF
100
TPC 2. Gain Error vs. Gain Control
TPC 4. AC Response for Various Capacitor Loads
36 OUTPUT NOISE - dBmV in 160 kHz BW 30 24 18
GAIN - dB
GC128 GC64 GC32 GC16 GC8 GC4 GC2 GC1
-32
f = 10MHz PD = 1
-36
12 6 0 -6 -12 -18 1
-40
-44
-48 10 100 FREQUENCY - MHz 1k 1 2 4 8 16 32 64 128 GAIN CODE - Decimal
TPC 3. AC Response vs. Gain Control
TPC 5. Output Noise vs. Gain Code
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AD8322
0 PD = 0 -10 -20 FEEDTHROUGH - dBc -30
IMPEDANCE -
170 170 PD = 1 MAX GAIN 150 PD = 0 130 110 90 70
-40 -50 -60 -70 -80 -90 -100 1 10 100 FREQUENCY - MHz 1k GAIN CODE 0 MIN GAIN
50 30
1
10 100 FREQUENCY - MHz
1k
TPC 6. Input Signal Feedthrough vs. Frequency
TPC 9. Input Impedance vs. Frequency (Inputs Shunted with 432 )
-45 PO = 62dBmV at MAX GAIN -50 DISTORTION - dBc PO = 60dBmV at MAX GAIN -55
150
125
IMPEDANCE -
100
75
PD = 0 PD = 1
-60
PO = 58dBmV at MAX GAIN
50
-65 5
15
25 35 45 55 FUNDAMENTAL FREQUENCY - MHz
65
25 0.1
1
10 FREQUENCY - MHz
100
1k
TPC 7. Second Order Harmonic Distortion vs. Frequency for Various Output Levels
TPC 10. Output Impedance vs. Frequency
-45 PO = 62dBmV at MAX GAIN -50 DISTORTION - dBc PO = 60dBmV at MAX GAIN
-55
-60
-65 PO = 58dBmV at MAX GAIN -70
-75 5
15
25 35 45 55 FUNDAMENTAL FREQUENCY - MHz
65
TPC 8. Third Order Harmonic Distortion vs. Frequency for Various Output Levels
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AD8322
APPLICATIONS General Application
The AD8322 is primarily intended for use as the upstream power amplifier (PA) in DOCSIS (Data Over Cable Service Interface Specifications) certified cable modems and CATV set-top boxes. Upstream data is modulated in QPSK or QAM format. This is done with DSP or a dedicated QPSK/QAM modulator. The amplifier receives its input signal from the QPSK/QAM modulator or from a DAC. In either case the signal must be low-pass filtered before being applied to the amplifier. Because the distance from the cable modem to the central office will vary with each subscriber, the AD8322 must be capable of varying its output power by applying gain or attenuation to ensure that all signals arriving at the central office are of the same amplitude. The upstream signal path contains components such as a transformer and diplexer that will result in some amount of power loss. Therefore, the amplifier must be capable of providing enough power into a 75 load to overcome these losses without sacrificing the integrity of the output signal.
Operational Description
from decimal 1-128 (decimal values 1, 2, 4, 8, 16, 32, 64, 128). The resulting gain for each code can be seen in Table I. Although the AD8322 is designed for use with the previous eight codes, the intermediate codes can be used. The gain transfer function is as follows: AV = 20 x LOG (0.2332 x CODE) for 1 CODE 128 AV = 29.5 dB for CODE 128 where AV is the gain in dB and CODE is the decimal equivalent of the 8-bit word. Figure 4 shows the gain characteristic for all possible values (except 0) in an 8-bit word. Code 0 may be used if more feedthrough isolation is required. It typically provides -85 dB of isolation across the 5 MHz to 65 MHz upstream band.
35 30 25 20 15
GAIN - dB
The AD8322 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 amplitudes. This will ensure the proper gain accuracy and harmonic performance. The preamp stage drives a DAC, which provides the bulk of the AD8322's attenuation (7 bits or 42.14 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, which amplifies these currents to the appropriate levels necessary to drive a 75 load. The output stage utilizes negative feedback to implement a differential 75 output impedance. This eliminates the need for external matching resistors.
SPI Programming and Gain Adjustment
10 5 0 -5 -10 -15 -20 0 32 64 96 128 160 GAIN CODE - Decimal 192 224 256
Figure 4. Gain vs. Gain Code
Input Bias, Impedance, and Termination
Gain programming of the AD8322 is accomplished using a serial peripheral interface (SPI) and three digital control lines, DATEN, SDATA, and CLK. To change the gain, eight bits of data are streamed into the serial shift register through the SDATA port. The SDATA load sequence begins with a falling edge on the DATEN pin, thus activating the CLK line. Although the CLK line is now activated, no change in gain is observed. 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 each CLK pulse. A rising edge on the DATEN line latches the contents of the shift register into the attenuator core resulting in a well-controlled change in the output signal level. The serial interface timing for the AD8322 is shown in Figures 2 and 3. The programmable gain range of the AD8322 is -12.64 dB to +29.5 dB and scales 6.02 dB for each major carry. Because the AD8322 was characterized with a TOKO transformer, the stated gain values already take into account the losses associated with the transformer. Valid gain codes are the major carries
The VIN+ and VIN- inputs have a dc bias level of approximately VCC/2, therefore the input signal should be ac-coupled. The differential input impedance is approximately 235 while the single-ended input impedance is 210 . If the AD8322 is being operated in a single-ended input configuration with a desired input impedance of 75 , the VIN+ and VIN- inputs should be terminated as shown in Figure 5. For input impedances other than 75 , the value of R1 in Figure 5 can be calculated using the following equation: Z IN = R1 210
ZIN = 75
R1 = 118
AD8322
Figure 5. Single-Ended Input Termination
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AD8322
5V 10 F 25V SDATA CLK DATEN 0.1 F 0.1 F PD 0.1 F 0.1 F 1 2 3 4 5 6 7 8 9 10 11 12 13 14
AD8322TSSOP
SDATA CLK DATEN GND1 BYP VCC PD VCC1 VCC2 OUT- GND2 GND3 GND4 GND5 GND12 VCC6 VIN- VIN+ GND11 VCC5 GND10 VCC4 VCC3 OUT+ GND9 GND8 GND7 GND6
0.1 F 28 27 26 25 24 23 22 21 20 19 18 17 16 15 0.1 F 0.1 F 0.1 F VIN+ 0.1 F VIN- ZIN = 150 432
0.1 F
0.1 F
0.1 F
TOKO 617DB-A0070
TO DIPLEXER ZIN = 75
Figure 6. Typical Applications Circuit
Output Bias, Impedance, and Termination
The differential output pins VOUT+ and VOUT- are also biased to a dc level of approximately VCC/2. Therefore, the outputs should be ac-coupled before being applied to the load. This may be accomplished by connecting 0.1 F capacitors in series with the outputs as shown in the typical applications circuit of Figure 6. The differential output impedance of the AD8322 is internally maintained at 75 , regardless of whether the amplifier is in forward transmit mode or reverse power-down mode, eliminating the need for external back termination resistors. A 1:1 transformer (TOKO #617DB-A0070) is used to couple the amplifier's differential output to the coaxial cable while maintaining a proper impedance match. If the output signal is being evaluated on standard 50 test equipment, a 75 to 50 pad must be used to provide the test circuit with the correct impedance match.
Power Supply Decoupling, Grounding, and Layout Considerations
minimize coupling (crosstalk) through the board. Following these guidelines will improve the overall performance of the AD8322 in all applications.
Initial Power-Up
When the 5 V supply is first applied to the VCC pins of the AD8322, the gain setting of the amplifier is indeterminate. Therefore, as power is first applied to the amplifier, the PD pin should be held low (Logic 0) thus preventing forward signal transmission. After power has been applied to the amplifier, the gain can be set to the desired level by following the procedure in the SPI Programming and Gain Adjustment section. The PD pin can then be brought from Logic 0 to 1, enabling forward signal transmission at the desired gain level.
Asynchronous Power-Down
Careful attention to printed circuit board layout details will prevent problems due to associated board parasitics. Proper RF design technique is mandatory. The 5 V supply power 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 with a 10 F tantalum capacitor located in close proximity to the AD8322. In addition to the 10 F capacitor, each VCC pin should be individually decoupled to ground with a 0.1 F ceramic chip capacitor located as close to the pin as possible. The pin labeled BYP (Pin 5) 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 component side of the board, except in the area of the input and output traces (see Figure 11). It is important to connect all of the AD8322 ground pins to ensure proper grounding of all internal nodes. The differential input and output traces should be kept as short and as symmetrical as possible. In addition, the input and output traces should be kept far apart in order to
The asynchronous PD pin is used to place the AD8322 into "Between Burst" mode while maintaining a differential output impedance of 75 . Applying a Logic 0 to the PD pin activates the on-chip reverse amplifier, providing a 52% reduction in consumed power. The supply current is reduced from approximately 113 mA to approximately 54 mA. In this mode of operation, between burst noise is minimized and the amplifier can no longer transmit in the upstream direction.
Distortion, Adjacent Channel Power, and DOCSIS
In order to deliver 58 dBmV of high-fidelity output power required by DOCSIS, the PA should be able to deliver about 60 to 61 dBmV in order to make up for losses associated with the transformer and diplexer. It should be noted that the AD8322 was characterized with the TOKO 617DB-A0070 transformer. TPC 7 and TPC 8 show the AD8322 second and third 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 will be sharply attenuated by the low-pass filter function of the diplexer. Another measure of signal integrity is adjacent channel power or ACP. DOCSIS section 4.2.9.1.1 states, "Spurious emissions from a transmitted carrier may occur -8- REV. 0
AD8322
in an adjacent channel which could be occupied by a carrier of the same or different symbol rates." Figure 7 shows the measured ACP, for a 16 QAM, 60 dBmV signal, taken at the output of the AD8322 evaluation board (see Figure 13 for evaluation board schematic). The transmit channel width and adjacent channel width in Figure 7 correspond to symbol rates of 160 KSYM/SEC. Table II shows the ACP results for the AD8322 for all conditions in DOCSIS Table 4-7 "Adjacent Channel Spurious Emissions."
-10 -20 -30 -40 -50 -60 -70 CL1 -80 CENTER 10MHz CL1 60kHz CU1 F1 SPAN 600kHz C0 C0 CU1 RBW 500Hz RF ATT 40dB VBW 5kHz SWT 12s UNIT dBm CH PWR 5.39dBm ACP UP -54.22dB ACP LOW -56.84dB
Evaluation Board Features and Operation
The AD8322 evaluation board (Part # AD8322-EVAL) and control software can be used to control the AD8322 upstream cable driver via the parallel port of a PC. A standard printer cable connected between the parallel port and the evaluation board is used to feed all the necessary data to the AD8322 by means of the Windows(R) based, Microsoft Visual Basic control software. This package provides a means of evaluating the amplifier by providing a convenient way to program the gain/attenuation as well as offering easy control of the amplifiers asynchronous PD pin. With this evaluation kit the AD8322 can be evaluated with either a single-ended or differential input configuration. The amplifier can also be evaluated with or without the PULSE diplexer in the output signal path. To remove the diplexer from the signal path, move the two 0 chip resistors R18 and R10 to locations R11 and R20. A schematic of the evaluation board is provided in Figure 13.
Overshoot on PC Printer Ports
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 AD8322 (TP5 on the evaluation board). The evaluation board was designed to accommodate a series resistor and shunt capacitor (R1 and C15) to filter the CLK signal if required.
Transformer and Diplexer
Figure 7. Adjacent Channel Power Table II. ACP Performance for All DOCSIS Conditions (All Values in dBc)
ADJACENT CHANNEL SYMBOL RATE TRANSMIT CHANNEL 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
-54.2 -54.7 -55.4 -54.6 -54.5 -53.9 -54.2 -56.6 -55.1 -54.4 -54.3 -53.8 -55.9 -54.8 -54.1 -53.7 -53.5
-53.8
-54.0 -53.9 -54.2
-54.6
-54.1 -54.1 -54.2
A 1:1 transformer is needed to couple the differential outputs of the AD8322 to the cable while maintaining a proper impedance match. The specified transformer is available from TOKO (Part # 617DB-A0070), however, MA/COM part # ETC-1-1T-15 can also be used. The evaluation board is equipped with the TOKO transformer, but is also designed to accept the MA/COM transformer. The PULSE diplexer included on the evaluation board provides a high-order low-pass filter function, typically used in the upstream path. The ability of the PULSE diplexer to achieve DOCSIS compliance is neither expressed nor implied by Analog Devices Inc. Data on the diplexer should be obtained from PULSE.
Differential Inputs
Noise and DOCSIS
At minimum gain, the AD8322's output noise spectral density is 12 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 power in dBmV for 160 KSYM/SEC is: 2 20 log 12 nV x 160 kHz + 60 = -46.4 dBmV Hz Comparing the computed noise power of -46.4 dBmV to the 8 dBmV signal yields -54.4 dBc, which meets the required level of -53 dBc set forth in DOCSIS Table 4-8. As the AD8322's gain is increased from this minimum value, the output signal increases at a faster rate than the noise, resulting in a signal-tonoise ratio that improves with gain. In transmit disable mode the output noise spectral density computed over 160 KSYM/SEC is 1.0 nV/Hz or -68 dBmV.
The AD8322-EVAL evaluation board is designed to accommodate a Mini-Circuits T1-6T-KK81 1:1 transformer for the purpose of converting a single-ended (ground referenced) input signal to differential inputs. Figure 8 and the following paragraphs identify three options for providing differential input signals to the AD8322 evaluation board.
Windows is a registered trademark of Microsoft Corporation.
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AD8322
Single-Ended-to-Differential Input (Figure 8 Option 1) Installing the Visual Basic Control Software
Install the Mini-Circuits T1-6T-KK81 1:1 transformer in the T1 location of the evaluation board. Install 0 chip resistors in R12, R13, and R17, and leave R14, R16, and R19 open. For 75 input impedance, install a 110 resistor in R7 located on the back side of the evaluation board and leave R5 and R6 open. In this configuration the input signal must be applied to the VIN+ port of the evaluation board from a single-ended 75 signal source. For input impedances other than 75 , use the following equation to compute the correct value for R7. Desired Input Impedance = R7 235
Single-Ended-to-Differential Input (Figure 8 Option 2)
To install the "CABDRIVE_22" evaluation board control software, first close all Windows applications and run "SETUP.EXE" located on Disk 1 of the AD8322 Evaluation Software. Follow the on-screen instructions and insert Disk 2 when prompted to do so. Enter the path of the directory into which the software will be installed and select the button in the upper left corner to complete the installation.
Running the Software
To invoke the control software, go to START -> PROGRAMS -> CABDRIVE_22, or select the AD8322.EXE icon from the directory containing the software.
Controlling the Gain/Attenuation of the AD8322
Install the Mini-Circuits T1-6T-KK81 1:1 transformer in the T1 location of the evaluation board. Install 0 chip resistors in R12, R13, R17, and R19, and leave R14 and R16 open. For 75 input impedance, install 55 resistors in R5 and R6 located on the back side of the evaluation board and leave R7 open. In this configuration the input signal must be applied to the VIN+ port of the evaluation board from a single-ended 75 signal source. For input impedances other than 75 , use the following equation to compute the correct values for R5 and R6. R5 = R6 = R, Desired Input Impedance = 2 x (R 117.5)
Differential Input (Figure 8 Option 3)
The slide bar controls the AD8322's gain/attenuation, which is displayed in dB and in V/V. Although the AD8322 is designed for use at the eight gain codes described in the SPI Programming and Gain Adjustment section, all of the intermediate codes are included in the software. Code 0 is also included because of the high isolation it provides. The gain code (i.e., position of the slide bar) is displayed in decimal, binary, and hexadecimal (see Figure 9).
POWER-UP AND POWER-DOWN
If a differential signal source is available, it may be applied directly to both the VIN+ and VIN- input ports of the evaluation board. In this case, install 0 chip resistors in R8, R14, R15, and R16, and leave R12, R13, and R19 open. Referring to Figure 8 Option 3 and the AD8322 evaluation board, a differential input impedance of 150 can be achieved by installing a 432 resistor in R7, leaving R5 and R6 open. If another input impedance is desired, the following equation can be used to compute the correct value for R7. Desired Input Impedance = R7 235
DIFF IN T1 R7
The "Power-Up" and "Power-Down" buttons select the mode of operation of the AD8322 by controlling the logic level on the asynchronous PD pin. The "Power-Up" button applies a Logic 1 to the PD pin putting the AD8322 in forward transmit mode. The "Power-Down" button applies a Logic 0 to the PD pin selecting reverse mode, where the forward signal transmission is disabled while a back termination of 75 is maintained.
Memory Section
AD8322
The "MEMORY" section of the software provides a convenient 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 that level. The "X->M2" and "RM2" buttons work in the same manner.
OPTION 1 DIFFERENTIAL INPUT TERMINATION
R6 DIFF IN T1
AD8322
R5
OPTION 2 DIFFERENTIAL INPUT TERMINATION
VIN+ R7 VIN-
AD8322
OPTION 3 DIFFERENTIAL INPUT TERMINATION
Figure 8. Differential Input Termination Options
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AD8322
Figure 9. Screen Display of Windows-Based Control Software
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AD8322
Figure 10. Evaluation Board--Assembly (Component Side)
Figure 11. Evaluation Board Layout (Component Side)
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AD8322
Figure 12. Evaluation Board--Solder Side
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AD8322
J1
VCC 1
TP15 RED + C18 10 F 25V SDATA CLK DATEN C1 0.1 F 1 2 3 4 5 6 7 8 9 10 11 12 13 14 28 GND12 SDATA 27 VCC6 CLK 26 VIN- DATEN 25 VIN+ GND1 24 GND11 BYP 23 VCC5 VCC 22 GND10 PD U1 21 VCC4 VCC1 20 VCC3 VCC2 19 OUT+ OUT- 18 GND9 GND2 17 GND8 GND3 16 GND7 GND4 15 GND6 GND5 TP14 YEL
TP20 BLK J2 1
C8
0.1 F
C13 0.1 F R5 DNI
R14 0
R8 0
VIN- S2
C7 C6 C5
0.1 F 0.1 F 0.1 F
R13 DNI R19 DNI
3 2 1
NC = 5
4
R9 DNI
AGND
PD C3 C4 C2 0.1 F 0.1 F 0.1 F
1:1 6 T1 R17 DNI R16 0
18 17 16 15 14 13 12 11 10
Figure 13. Evaluation Board Schematic
C12 0.1 F R6 0
R7 118
R12 DNI R15 0
VIN+ S3
AD8322TSSOP
TP3 WHT AMP-552742 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 P1 DATEN TP4 R2 WHT 0 C14 DNI TP2 SDATA R1 WHT 0 C15 DNI TP5 WHT CLK 3 2 TP17 WHT TP19 WHT TP7 DNI TP8 DNI C10 0.1 F 1 TP6 WHT PD TP12 DNI C11 0.1 F TP11 DNI
TP13 YEL
G1 G2 G3 G4 G5 G6 G7 G8 G9
U2
A-B
TP1 WHT
TP9 DNI C16 DNI ETCC1-1T 4 5 TOKO-B4F NC = 2 4 R18 0
1 A
TP22 DNI R10 0 R11 DNI R20 DNI
9 PULSEB5008
3
5
B
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TP21 HPP DNI S4
1:1 T2A DNI C9 DNI 5 1
1:1 3 T2B
TP10 DNI R3 0 R4 DNI
CABLE S1
AD8322
EVALUATION BOARD BILL OF MATERIALS
AD8322 Evaluation Board Rev. DC SINGLE-ENDED INVERTING INPUT - Revised - June 22, 2000 Qty. 1 12 10 1 8 1 1 2 4 1 2 1 1 1 1 4 4 2 2 2 2 Description 10 F 16 V. `C' size tantalum chip capacitor 0.1 F 50 V. 1206 size ceramic chip capacitor 0 1/8 W. 1206 size chip resistor 118 1% 1/8 W. 1206 size chip resistor White Test Point (CLK, PD, CP, SDATA, DATEN) Black Test Point (GND) Red Test Point (VCC) Yellow Test Point (+/- INPUT) 75 right-angle BNC Telegartner # J01003A1949 Centronics type 36-pin Right-Angle female connector 5-way Metal Binding Post TOKO # 617 DB-A0070 transformer Diplexer PULSE* AD8322 (TSSOP) AD8322 REV. E Evaluation PC board #4 - 40 x 1/4 inch ss panhead machine screw #4 - 40 x 3/4 inch long aluminum round stand-off # 2 - 56 x 3/8 inch ss panhead machine screw # 2 steel flat washer # 2 steel internal tooth lockwasher # 2 ss hex. machine nut Vendor ADS# 4-7-6 ADS# 4-5-18 ADS# 3-18-88 ADS# 3-18-106 ADS# 12-18-42 ADS# 12-18-44 ADS# 12-18-43 ADS# 12-18-32 ADS# 12-6-28 ADS# 12-3-50 ADS# 12-7-7 Toko # 617DB-A0070 PULSE ADS# AD8322 D.S.C. ADS# 30-1-1 ADS# 30-16-3 ADS# 30-1-17 ADS# 30-6-6 ADS# 30-5-2 ADS# 30-7-6 Ref Desc. C18 C1-8, 10-13 R1, 2, 3, 6, 8, 10, 14-16, 18 R7 TP1-6, 17, 19 TP20 TP15 TP13 & TP14 S1-4 (INPUT, OUTPUT) P1 J1, 2 (VCC, GND) T2B U2 D.U.T. (U1) Evaluation PC board
(p1 hardware) (p1 hardware) (p1 hardware) (p1 hardware)
DO NOT INSTALL C9, C14-C16, TP7-TP12, TP21, TP22, R4, R5, R9, R11-R13, R17, R19, R20, T1, T2A. *PULSE Diplexer Part #'s B5008 (42 MHz), CX6002 (42 MHz), B5009 (65 MHz).
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AD8322
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
28-Lead TSSOP (RU-28)
0.386 (9.80) 0.378 (9.60)
28
15
0.177 (4.50) 0.169 (4.30) 0.256 (6.50) 0.246 (6.25)
1 14
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.
C02049-2.5-7/00 (rev. 0)

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