Digital phase tightening for millimeter-wave imaging

A new technique called digital phase tightening reduces phase noise from receiver front-end circuits to allow precise phase estimation for digital beamforming in millimeter-wave (MMW) imaging applications. This is achieved by leveraging the large ratio between the MMW carrier frequency and the relatively low frame rates in imaging applications. By mixing down to an intermediate frequency (IF) and then averaging over many samples to estimate the phase, we reduce phase noise and attain phase error of the MMW beamformer in the femtosecond range. A test chip demonstrating the phase tightening concept was designed and fabricated using 0.13μm CMOS, and we show that an RMS error of 3.5fs is feasible with this technique.