5 V CATV Line Driver Fine Step a Output Power Control AD8325 FEATURES FUNCTIONAL BLOCK DIAGRAM Supports DOCSIS Standard for Reverse Path V (7 PINS) BYP CC Transmission Gain Programmable in 0.75 dB Steps Over a 59.45 dB R1 AD8325 Range Low Distortion at 61 dBmV Output V IN+ V OUT+ DIFF OR 57 dBc SFDR at 21 MHz POWER ATTENUATION SINGLE VERNIER AMP CORE INPUT 55 dBc SFDR at 42 MHz V V IN AMP OUT Output Noise Level Z DIFF = OUT 8 75 48 dBmV in 160 kHz R2 DECODE Maintains 75 Output Impedance Z (SINGLE) = 800 IN 8 POWER-DOWN Transmit Enable and Transmit Disable Modes Z (DIFF) = 1.6k IN LOGIC DATA LATCH Upper Bandwidth: 100 MHz (Full Gain Range) 8 5 V Supply Operation SHIFT Supports SPI Interfaces REGISTER APPLICATIONS Gain-Programmable Line Driver TXEN DATEN DATACLK GND (11 PINS) SLEEP DOCSIS High-Speed Data Modems Interactive Cable Set-Top Boxes PC Plug-in Cable Modems General-Purpose Digitally Controlled Variable Gain Block GENERAL DESCRIPTION The AD8325 is a low-cost, digitally controlled, variable gain ampli fier optimized for coaxial line driving applications such as cable modems that are designed to the MCNS-DOCSIS upstream 50 V = 62dBmV OUT standard. An 8-bit serial word determines the desired output gain MAX GAIN 52 over a 59.45 dB range resulting in gain changes of 0.7526 dB/LSB. V = 61dBmV OUT MAX GAIN The AD8325 comprises a digitally controlled variable attenuator 54 of 0 dB to 59.45 dB, which is preceded by a low noise, fixed gain buffer and is followed by a low distortion high power ampli 56 fier. The AD8325 accepts a differential or single-ended input signal. The output is specified for driving a 75 W load, such as 58 coaxial cable. 60 Distortion performance of 57 dBc is achieved with an output V = 60dBmV OUT level up to 61 dBmV at 21 MHz bandwidth. A key performance MAX GAIN 62 and cost advantage of the AD8325 results from the ability to V = 59dBmV OUT MAX GAIN maintain a constant 75 W output impedance during Transmit 64 5 15 25 35 45 55 65 Enable and Transmit Disable conditions. In addition, this FUNDAMENTAL FREQUENCY MHz device has a sleep mode function that reduces the quiescent current to 4 mA. Figure 1. Worst Harmonic Distortion vs. Gain Control The AD8325 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. 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. may result from its use. No license is granted by implication or otherwise Tel: 781/329-4700 www.analog.com under any patent or patent rights of Analog Devices. Trademarks and Fax: 781/461-3113 2005 Analog Devices, Inc. All rights reserved. registered trademarks are the property of their respective owners. DISTORTION dBc(T = 25C, V = 5 V, R = 75 , V (differential) = 31 dBmV, V measured through AD8325SPECIFICATIONS A S L IN OUT 1 a 1:1 transformer with an insertion loss of 0.5 dB 10 MHz unless otherwise noted.) Parameter Conditions Min Typ Max Unit INPUT CHARACTERISTICS Specified AC Voltage Output = 61 dBmV, Max Gain 31 dBmV Noise Figure Max Gain, f = 10 MHz 13.8 dB Input Resistance Single-Ended Input 800 W Differential Input 1600 W Input Capacitance 2 pF GAIN CONTROL INTERFACE Gain Range 58.45 59.45 60.45 dB Maximum Gain Gain Code = 79 Dec 29.2 30.0 30.8 dB Minimum Gain Gain Code = 0 Dec 30.25 29.45 28.65 dB Gain Scaling Factor 0.7526 dB/LSB OUTPUT CHARACTERISTICS Bandwidth (3 dB) All Gain Codes 100 MHz Bandwidth Roll-Off f = 65 MHz 1.6 dB Bandwidth Peaking f = 65 MHz 0 dB Output Noise Spectral Density Max Gain, f = 10 MHz 33 dBmV in 160 kHz Min Gain, f = 10 MHz 48 dBmV in 160 kHz Transmit Disable Mode, f = 10 MHz 68 dBmV in 160 kHz 1 dB Compression Point Max Gain, f = 10 MHz 18.5 dBm Differential Output Impedance Transmit Enable and Transmit Disable Modes 75 20% W OVERALL PERFORMANCE Second Order Harmonic Distortion f = 21 MHz, V = 61 dBmV Max Gain 70 dBc OUT f = 42 MHz, V = 61 dBmV Max Gain 67 dBc OUT f = 65 MHz, V = 61 dBmV Max Gain 60 dBc OUT Third Order Harmonic Distortion f = 21 MHz, V = 61 dBmV Max Gain 57 dBc OUT f = 42 MHz, V = 61 dBmV Max Gain 55 dBc OUT f = 65 MHz, V = 61 dBmV Max Gain 54 dBc OUT Adjacent Channel Power Adjacent Channel Width = Transmit Channel 53.8 dBc Width = 160 K SYM/SEC Gain Linearity Error f = 10 MHz, Code to Code 0.3 dB Output Settling Due to Gain Change (T) Min to Max Gain 60 ns GS Due to Input Change Max Gain, V = 31 dBmV 30 ns IN Isolation in Transmit Disable Mode Max Gain, TXEN = 0 V, f = 42 MHz, 33 dBc V = 31 dBmV IN POWER CONTROL Transmit Enable Settling Time (T ) Max Gain, V = 0 V 300 ns ON IN Transmit Disable Settling Time (T ) Max Gain, V = 0 V 40 ns OFF IN 2 Between Burst Transients Equivalent Output = 31 dBmV 3 mV p-p Equivalent Output = 61 dBmV 50 mV p-p POWER SUPPLY Operating Range 4.75 5 5.25 V Quiescent Current Transmit Enable Mode (TXEN = 1) 123 133 140 mA Transmit Disable Mode (TXEN = 0) 30 35 10 mA Sleep Mode 2 4 7 mA OPERATING TEMPERATURE 40 +85 C RANGE NOTES 1 TOKO 617DB-A0070 used for above specifications. MACOM ETC-1-IT-15 can be substituted. 2 Between Burst Transients measured at the output of a 42 MHz diplexer. Specifications subject to change without notice. 2 REV. A