AD8321

The AD8321 is a low cost digitally controlled variable gain amplifier optimized for coaxial line driving applications such as cable modems that are designed to the DOCSIS* (upstream) standard. An 8-bit serial word determines the desired output gain over a 53.4 dB range, resulting in gain changes of 0.75 dB/LSB.

The AD8321 comprises a digitally controlled variable attenuator of 0 dB to 53.4 dB, which is preceded by a low noise, fixed gain buffer and followed by a low distortion high power amplifier.The AD8321 accepts a differential or single-ended input signal. The output is specified for driving a 75 load, such as coaxial cable, although the AD8321 is capable of driving other loads. Performance of 53 dBc is achieved with an output level up to 11 dBm at 42 MHz bandwidth using a 9 V supply.

A key performance and cost advantage of the AD8321 results from the ability to maintain a constant 75 output impedance during power-up and power-down conditions. This eliminates the need for external 75 termination, resulting in twice the effective output voltage when compared to a standard operational amplifier, thus eliminating the need for a transformer.The AD8321 is packaged in a low cost 20-lead SOIC, operates from a single +9 V supply, and has an operational temperature range of 40°C to +85°C.