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AD8325 Fiches technique(PDF) 1 Page - Analog Devices |
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AD8325 Fiches technique(HTML) 1 Page - Analog Devices |
1 / 16 page a 5 V CATV Line Driver Fine Step Output Power Control AD8325 FEATURES FUNCTIONAL BLOCK DIAGRAM Supports DOCSIS Standard for Reverse Path VCC (7 PINS) BYP Transmission Gain Programmable in 0.75 dB Steps Over a 59.45 dB Range Low Distortion at 61 dBmV Output VIN+ –57 dBc SFDR at 21 MHz DIFF OR SINGLE INPUT AMP ATTENUATION CORE ZOUT DIFF = 75 � 8 8 8 ZIN (SINGLE) = 800� ZIN (DIFF) = 1.6k� R1 R2 AD8325 VERNIER DECODE DATA LATCH SHIFT REGISTER POWER-DOWN LOGIC POWER AMP Output Noise Level –48 dBmV in 160 kHz Maintains 75 � Output Impedance Transmit Enable and Transmit Disable Modes Upper Bandwidth: 100 MHz (Full Gain Range) 5 V Supply Operation Supports SPI Interfaces APPLICATIONS Gain-Programmable Line Driver –55 dBc SFDR at 42 MHz VIN– VOUT+ VOUT– 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 standard. An 8-bit serial word determines the desired output gain over a 59.45 dB range resulting in gain changes of 0.7526 dB/LSB. –52 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 fier. The AD8325 accepts a differential or single-ended input signal. The output is specified for driving a 75 W load, such as coaxial cable. –56 –58 Distortion performance of –57 dBc is achieved with an output –60 level up to 61 dBmV at 21 MHz bandwidth. A key performance –62 and cost advantage of the AD8325 results from the ability to maintain a constant 75 W output impedance during Transmit –64 DATEN DATACLK GND (11 PINS) TXEN SLEEP VOUT VOUT = 62dBmV @ MAX GAIN = 61dBmV @ MAX GAIN VOUT = 60dBmV @ MAX GAIN VOUT = 59dBmV @ MAX GAIN Enable and Transmit Disable conditions. In addition, this 5 15 25 35 45 55 device has a sleep mode function that reduces the quiescent FUNDAMENTAL FREQUENCY – MHz 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 –40 ∞C to +85∞C. 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. No license is granted by implication or otherwise One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. under any patent or patent rights of Analog Devices. Trademarks and Tel: 781/329-4700 www.analog.com registered trademarks are the property of their respective owners. Fax: 781/461-3113 © 2005 Analog Devices, Inc. All rights reserved. 65 |
Numéro de pièce similaire - AD8325_05 |
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Description similaire - AD8325_05 |
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