10-Bit Broadband Modem Mixed Signal Front End (MxFE®)
The Tx signal path consists of a bypassable 2×/4× low-pass interpolation filter, a 10-bit TxDAC®, and a line driver. The transmit path signal bandwidth can be as high as 34 MHz at an input data rate of 80 MSPS. The TxDAC provides differential current outputs that can be steered directly to an external load or to an internal low distortion current amplifier. The current amplifier (IAMP) can be configured as a current or voltage mode line driver (with two external npn transistors) capable of delivering in excess of 23 dBm peak signal power. Tx power can be digitally controlled over a 19.5 dB range in 0.5 dB steps.
The receive path consists of a programmable amplifier (RxPGA), a tunable low pass filter (LPF), and a 10-bit ADC. The low noise RxPGA has a programmable gain range of −12 dB to +48 dB in 1 dB steps. Its input referred noise is less than 3.0 nV/ rtHz for gain settings beyond 36 dB. The receive path LPF cut-off frequency can either be set over a 15 MHz to 35 MHz range or simply bypassed. The 10-bit ADC achieves excellent dynamic performance over a 5 MSPS to 80 MSPS span. Both the RxPGA and the ADC offer scalable power consumption allowing power/performance optimization.
The AD9865 provides a highly integrated solution for many broadband modems. It is available in a space-saving 64-pin chip scale package and is specified over the commercial (−40°C to +85°C) temperature range.