Oscillator having all-pass filter with resistance bridge for detecting physical parameters

US4739285A · kind A · utility

Assignee

• U.S. Philips Corporation · US

Inventors

• Bernd Heck · Hamburg, DE
• Dierk Schröder · Ahlhorn, DE

Key dates

• Filing date: Mar 17, 1987
• Grant date: Apr 19, 1988
• Expiry date: Mar 17, 2007

Classification

• Technology area (CPC G): Physics
• CPC primary: G01L9/04
• WIPO field: Measurement
• WIPO sector: Instruments

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. The second pole (11) of the bipolar circuit (10) is connected to the junction of the two resistance elements (31, 30) of the bridge circuit. A variation of a resistance element of the bridge circuit due to a variation of the physical parame…