The AD8326 is a high-output power, digitally controlled, variable
gain amplifier optimized for coaxial line driving applications
such as data and telephony cable modems that are designed to
the MCNS-DOCSIS upstream standard. An 8-bit serial word
determines the desired output gain over a 53.5 dB range resulting
in gain changes of 0.75 dB/LSB. The AD8326 is offered in
two models, each optimized to support the desired output power
and resulting performance.
The AD8326 comprises a digitally controlled variable attenuator
of 0 dB to –54 dB, that is preceded by a low noise, fixed-gain
buffer and is followed by a low distortion high-power amplifier.
The AD8326 accepts a differential or single-ended input signal.
The output is designed to drive a 75 Ω load, such as coaxial
cable, although the AD8326 is capable of driving other loads.
When driving 67 dBm into a 75 Ω load, the AD8326ARP
provides a worst harmonic of only –59 dBc at 21 MHz and
–57 dBc at 42 MHz. When driving 65 dBmV into a 75 Ω load,
the AD8326ARE provides a worst harmonic of only –62 dBc at
21 MHz and –60 dBc at 42 MHz.