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The AD8327 is a low-cost, digitally controlled, variable gainamplifier opTImized for coaxial line driving applicaTIons such ascable modems that are designed to the MCNS-DOCSISupstream standard. An 8-bit serial word determines the desiredoutput gain over a 48.16 dB range resulTIng in gain changes of6.02 dB/major carry.The AD8327 comprises a digitally controlled variable attenuatorof 0 dB to –48.16 dB, which is preceded by a low noise, fixedgain buffer and followed by a low distorTIon, high power amplifier.The AD8327 accepts a differential or single-ended inputsignal. The output is specified for driving a 75 Ω load, suchas coaxial cable.Distortion performance of –63 dBc is achieved with an outputlevel up to 60 dBmV at 21 MHz bandwidth. A key performanceand cost advantage of the AD8327 results from the ability tomaintain a constant 75 Ω output impedance during TransmitEnable and Transmit Disable conditions. In addition, thisdevice has a sleep mode function that reduces the quiescentcurrent to 5 mA.The AD8327 is packaged in a low-cost 20-lead TSSOP, operatesfrom a single 5 V supply, and has an operational temperaturerange of –40°C to +85°C.
