IF Digitizing IC
The AD9874 is a member of the company's Mixed-Signal Front End (MxFE) family, and is based on ADI's "smart partitioning" methodology a mixed-signal design technique that partitions the signal path according to performance-enhancing, rather than analog/digital boundaries. The AD9874 MxFE integrates all the functional blocks (excluding the LO and VCO) needed for IF-to-digital conversion in a narrowband superheterodyne receiver. This partitioning reduces IF filtering, enhances demodulation accuracy and delegates all modulation-specific functions to an external digital signal processor.
The AD9874 MxFE digitizes low level IF signals from 10 to 300 MHz with a bandwidth of up to 270 kHz. Typical noise figure is 8.7 dB SSB NF and linearity, as measured by third-order input intercept point (IIP3), is +0 dBm IIP3 (typical maximum bias). The AD9874 is notable for its power efficiency, 21.2 milliAmps versus 45 milliAmps for previous generations. The signal chain consists of a low noise amplifier, a mixer, a bandpass sigma-delta analog-to-digital converter, filters and automatic gain control (AGC) circuitry capable of 12 dB continuous gain adjustment. The high dynamic range and inherent anti-aliasing provided by the bandpass sigma-delta converter allow the AD9874 to cope with blocking signals 80 dB stronger than the desired signal. The AD9874 is fully programmable, providing register-based digital control of AGC and filter parameters, amplifier gain and bias currents through a serial peripheral interface (SPI) port.