AD9975

The AD9975 is a single-supply, broadband modem, mixed signal, front end (MxFE™) IC. The device contains a transmit path interpolation filter and DAC and a receive path PGA, LPF, and ADC required for a variety of broadband modem applications. Also on-chip is a PLL clock multiplier that provides all required clocks from a single crystal or clock input.

The TxDAC+ uses a digital 2* interpolation low-pass filter to oversample the transmit data and ease the complexity of analog reconstruction filtering. The transmit path bandwidth is 21 MHz when sampled at 100 MSPS. The 10-bit DAC provides differential current outputs. The DAC full-scale current can be adjusted from 2 to 20 mA by a single resistor, providing 20 dB of additional gain range.

The receive path consists of a PGA, LPF, and ADC. The programmable gain amplifier (PGA) has two modes of operation. One mode allows programming through the serial port and provides a gain range from 6 dB to +36 dB in 2 dB steps. The other mode allows the gain to be controlled through an asynchronous 3-pin port and offers a gain range from 0 dB to 48 dB in 8 dB steps with the use of an external gain stage. The receive path LPF cutoff frequency can be selected to either 12 MHz or 26 MHz. The filter cutoff frequency can also be tuned or bypassed where filter requirements differ. The 10-bit ADC uses a multistage differential pipeline architecture to achieve excellent dynamic performance with low power consumption.

The digital transmit and receive ports are multiplexed onto a 10-bit databus and have individual TX/RX clocks and TX/RX enable lines. This interface connects directly to Homelug 1.0 PHY/MAC chips from Intellon and Conexant.

The AD9975 is available in a space-saving 48-lead LQFP package. The device is specified over the commercial (40°C to +85°C) temperature range.