Circuitry for processing signals occurring in a heterodyne interferometer
First Claim
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1. 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; and
a 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.
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Abstract
A signal processing circuit for a reference signal occurring in a heterodyne interferometer and a measured signal. The underlying frequency modulation of the radiation source of the heterodyne interferometer results in phase jumps in both signals. Signal filtering of both the reference signal and the measured signal with a gate signal removes from both signals those signal components that have the same phase sign. Further simplification of the signal processing results from signal interpolation by band pass filters and signal down-mixing into a lower frequency range below the heterodyne frequency. The input signals processed by the circuit can be further processed by a conventional phase comparator.
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Citations
10 Claims
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1. 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:
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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; and a 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, and wherein the particular heterodyne frequency is an integer multiple of a modulation frequency of the modulation signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Current AssigneeRobert Bosch GmbH
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Original AssigneeRobert Bosch GmbH
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InventorsSteinlechner, Siegbert
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Primary Examiner(s)Font, Frank G.
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Assistant Examiner(s)NATIVIDAD, PHILIP SANA
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Application NumberUS09/380,229Time in Patent Office323 DaysField of Search356/349, 356/345US Class Current356/484CPC Class CodesG01B 2290/45 Multiple detectors for dete...G01B 9/02002 using two or more frequenciesG01B 9/02083 characterised by particular...G01S 17/34 using transmission of conti...G01S 17/36 with phase comparison betwe...
