Lock-in Amplifier and Method for Filtering a Measurement Signal Using Such an Amplifier

摘要

A lock-in amplifier with an additional phase-sensitive detector is provided. A measurement signal is mixed in a multiplicative fashion with a reference signal, which is phase-shifted by 90 degrees, for a modulation frequency. In order to reliably filter out interference signal portions in a widest possible dynamic range and, at the same time, minimize unavoidable influence on the useful signal portion, a control device is connected downstream of the additional phase-sensitive detector. The control device determines a control variable corresponding to the strength of the interference signal from the measurement signal mixed with the reference signal phase shifted by 90 degrees and uses the control variable to change the integration duration of the integrator proportionally to the control variable, a corresponding cut-off frequency of an equivalent low pass being coordinated automatically.