Patent ID: 6147763
Filing Date: 2000-11-14
Classification: G01B,G01S

Abstract:
A signal processing circuit for a reference signal and a measured signal, the reference signal occurring in a heterodyne interferometer, the signal processing circuit comprising:a modulator controlling a particular frequency of an optical beam using a modulation signal which has a predetermined modulation period, the optical beam being emitted by a radiation source;a first arrangement deriving a gate signal from the modulation signal, the gate signal having a period which is equal to the modulation period;a second arrangement receiving the reference signal and filtering the reference signal using the gate signal to generate a first filtered signal, the first filtered signal including first signal components, each of the first signal components having the same phase sign;a third arrangement receiving the measured signal and filtering the measured signal using the gate signal to generate a second filtered signal, the second filtered signal including second signal components, each of the second signal components having the same phase sign; anda phase comparator receiving the first and second filtered signals, and determining a phase difference between the reference signal and the measured signal,wherein the reference signal has a particular heterodyne frequency, and the measured signal has the particular heterodyne frequency, andwherein the particular heterodyne frequency is an integer multiple of a modulation frequency of the modulation signal.