Design, Simulation, and Implementation of Electronic Sections of Super-Heterodyne Interferometer

The use of super-heterodyne interferometers is a method for precision measurements in nano-metrology systems. According to the low-level measurement and base signals received by optical section of superheterodyne interferometer, the signal conditioner circuit is needed. In the signal conditioner section, the received signals are amplified and self-mixed. Then they are converted to the lower frequencies and are fed to the phase measurement section. In the phase measurement section, the displacement is detected according to the phase shift. In this paper, we design, simulate, and implement the circuits required for electronic part of interferometer by CMOS 0.5μm technology. These circuits include cascade low-noise amplifier to convert the photocurrents of avalanche photodiode to voltage signal, band-pass filters with bandwidth equal to the primary beat frequency, double-balanced mixer and low-pass filter to extract the secondary beat frequency. The results show that the amplifiers have 19.41dB gain and 2.7dB noise factor, mixers have RF/LO range between 80-2500MHz and IF range between DC to 1000MHz. In the phase measurement section, a low-noise circuitbased on time-to-digital converter (TDC) with 1ns resolution is designed and implemented to detect the displacement according to the phase shift.