UC Irvine

Frequency-domain diffuse optical spectroscopy systems require accurate phase measurement for precise calculation of optical properties of a medium. Different phase detectors and their drawbacks are examined and it is shown how the non-idealities in conventional phase detectors give rise to nonlinearities in the average voltage vs. phase characteristics. A novel circuit for precise phase detection between two signals with the same frequency is presented. The proposed circuit makes use of a pair of XNOR-type phase detectors, to which signal and quadrature reference clocks are applied. A decision circuit then selects which of the two XNORs is used for the output, which guarantees that the circuit will be well within its linear region. All the blocks are designed and simulated in 0.18 micron standard CMOS.