Circuit generating virtual earth for solid electrolyte sensor measuring exhaust gas concentration comprises analog circuit to convert generated pulse width modulated signal into virtual earth

摘要

The microcontroller (20) determines the actual value of the virtual earth (voltage) and generates a pulse width modulated (PWM) signal. An analog circuit (21) converts the PWM signal into a virtual earth. The desired value of the virtual earth is read out from a memory for constants (e.g. an EPROM, 27). Preferred Features: The constant memory is programmable and integral to the microcontroller, which incorporates a subtracter (26) determining a difference value ( DELTA VM) between actual- (VM-ist) and desired- (VM-soll) values of the virtual earth. The PWM unit (22) is controlled (28) to generate the PWM as a function of the difference signal ( DELTA VM). The analog auxiliary circuit (21) includes a filter circuit (23) converting the PWM signal into a DC signal and an impedance transformer (24) matching the output impedance of the microprocessor.