Abstract: A measuring oscillator for detecting different physical parameters has an all-pass filter (1) which drives a current source (16) having a controllable amplification factor and a control device (17). The control device is connected to the control input of the current source (16) and controls its amplification factor so that the amplitude of the alternating voltage produced by the measuring oscillator assumes a constant value. The all-pass filter comprises a phase-determining bipolar circuit (10) comprising a voltage follower (12) having its input connected to the first pole (9) of the circuit (10) and its output connected through bridge circuit (28) to the inputs of a differential amplifier circuit (33). The four resistance elements (29-32) of the bridge circuit have resistance values varying with the physical parameters to be detected. The output of the differential amplifier circuit is connected through an ohmic resistor (41) to the first pole.

Abstract: A measuring oscillator for measuring temperature has an all-pass filter (1) which drives a current source (16) having a controllable amplification factor and a control element (17). The control element is connected to the control input of the current source (16) and controls its amplification factor in a manner such that the amplitude of the alternating voltage produced by the measuring oscillator assumes a constant value. The all-pass filter comprises a phase-determining bipolar circuit arrangement (10) comprising a voltage follower (12), whose input is connected to one terminal (9) of the circuit arrangement (10) and whose output is connected through an ohmic input resistor (13) to the inverting input of a first operational amplifier (14), which is fed back negatively through a measuring resistor (15) having a temperature-dependent ohmic resistance value. The output of the first op-amp also is connected through an ohmic resistor (41) to the one terminal (9) of the bipolar circuit arrangement.