The AD9870 is a general-purpose IF subsystem that digitizes a low-level 10 MHz300 MHz IF input with a bandwidth of up to 150 kHz. The signal chain of the AD9870 consists of a low-noise amplifier, a mixer, a variable gain amplifier with integral antialias filter, a bandpass sigma-delta analog-to-digital converter, and a decimation filter with programmable decimation factor. An automatic gain control (AGC) circuit provides the AD9870 with 25 dB of continuous gain adjustment. The high dynamic range of the bandpass sigma-delta converter allows the AD9870 to cope with blocking signals that are as much as 70 dB stronger than the desired signal. Auxiliary blocks include clock and LO synthesizers as well as a serial peripheral interface (SPI) port. The SPI port programs numerous parameters of the AD9870, including the synthesizer divide ratios, the AGC attack and decay times, the AGC target signal level, the decimation factor, the output data format, the 16 dB attenuator, and the bias currents of several blocks. Reducing bias currents allows the user to reduce power consumption at the expense of reduced performance.