AD9879:  Mixed Signal Front End Set Top Box, Cable Modem (MxFE®)

The AD9879 is a single supply Cable Modem/Set Top Box Mixed Signal Front End. The device contains a transmit path interpolation filter, a complete quadrature digital upconverter and transmit DAC. The receive path contains a 12-bit ADC, a 10-bit ADC, and Dual 7-bit ADCs. All internally required clocks and an output system clock are generated by the PLL from a single crystal or clock input.

The AD9879 is an evolutionary product in the MxFE product portfolio, it is the next generation of the highly successful AD9873. The AD9879 features a lower price and several functional improvements when compared to the AD9873. These improvements include lower power consumption, improved IF under-sampling capability, output gain control in .5dB steps allowing the use of coarse gain output drivers, and improved tuning resolution; 3.2Hz resolution is provided. In addition, the 8-bit ADCs have been replaced with 7-bit devices to reduce cost while still providing sufficient performance for the out-of-band channel I&Q demodulation.

The transmit path interpolation filter provides an upsampling factor of 16x with an output signabandwidth as high as 8.3 MHz. Carrier frequencies up to 65 MHz with 26 bits of frequency tuning resolution can be generated by the direct digital synthesizer (DDS). The transmit DAC resolution is 12 bits and can run at sampling rates as high as 232 MSPS. Analog output scaling from 0 to 7.5dB in 0.5 dB steps is available to preserve SNR when reduced output levels are required.

The 12-bit and 10-bit IF ADCs can convert direct IF inputs up to 70 MHz and run at sample rates up to 33 MSPS. A video input with an adjustable signal clamping level along with the 10-bit ADC allow the AD9879 to process an NTSC and a QAM channel simultaneously.

The programmable sigma delta DAC can be used to control external components such as variable gain amplifiers (VGAs) or voltage controlled tuners. The CA PORT provides an interface to the AD8321/AD8323 or AD8322/AD8327 programmable gain amplifier (PGA) cable drivers enabling host processor control via the MxFE SPORT.

The AD9879 is available in a 100-pin MQFP package. It offers enhanced receive path undersampling performance and lower cost, compared with the pin compatible AD9873. The AD9879 is specified over the commercial (-40ºC to +85ºC) temperature range.