The AD8325 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.
The AD8325 is a digitally controlled variable gain line driver intended for DOCSIS‑compatible cable modems and set‑top boxes. It accepts differential or single‑ended inputs and drives a 75 Ω coaxial load, providing up to 61 dBmV output power.
Key features include a gain range of –29.45 dB to +30 dB in 0.7526 dB steps, SPI‑based programming, low‑distortion performance (‑57 dBc SFDR at 21 MHz), and a sleep mode that reduces quiescent current to 4 mA. The device is supplied in a 28‑lead TSSOP package and operates from a single 5 V supply.
| Gain range | -29.45 dB to +30 dB |
|---|---|
| Gain step size | 0.7526 dB per LSB |
| Maximum output voltage | 61 dBmV |
| Output noise spectral density (max gain, 10 MHz) | 33 dBmV in 160 kHz |
| Output impedance (TX enable/disable) | 75 Ω ±20 % |
| Supply voltage range | 4.75 V to 5.25 V |
| Quiescent current (TX enable) | 123 mA typical |
| Sleep mode current | 2 mA min – 7 mA max |
| Operating temperature range | -40 °C to +85 °C |
The gain changes in steps of 0.7526 dB per least‑significant bit.
Gain is programmed via an 8‑bit serial word over an SPI interface using the DATEN, SDATA, and CLK pins.
The device maintains a differential output impedance of 75 Ω ±20 % in both transmit‑enable and transmit‑disable modes.
It can deliver up to 61 dBmV at 21 MHz.