Monobit Subsampler for Digital Downconversion in Pulse-Doppler Radar Applications

This paper introduces a monobit RF subsampling technique for digital downconversion in pulse-Doppler radar systems. Design considerations for this application include the level of quantization imbalance given a noise-only input, the relation between input and output signal-to-noise ratio (SNR), the affect of jitter over the complete dynamic range of operation, and sensitivity to intermodulation distortion. An RF integrated circuit is designed to demonstrate the monobit subsampling approach. Measured results show excellent agreement with theoretical predictions. The device can detect a 495-MHz signal at input SNR levels less than -30 dB using a 1-MHz sampling clock. Excellent performance is maintained even in severe timing environments showing more than 400 ps of rms clock jitter.