AD8322

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 Ω 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 Ω output impedance during power-up and powerdown conditions. This eliminates the need for external 75 Ω 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 40°C to +85°C.