Circuit arrangement for compensating interference signals in the control loop of a linear lambda probe

1. A circuit arrangement for compensating interference signals in the control loop of a linear lambda probe comprising:

an evaluation circuit with a differential amplifier which forms the difference between a Nernst voltage which is subjected to an interference signal and a reference voltage,

a controller generating a controlling voltage from the difference wherein the controlling voltage is converted into a pumping current by a subsequent pumping current source said pumping current being fed back to said linear lambda probe,

a compensation circuit, coupled between the output of the differential amplifier and the input of the controller, for generating a compensation signal which is approximated in its curve profile to the interference signal and has an amplitude and frequency which are identical to the interference signal but phase-shifted through 180°, and for subtracting the compensation signal from the differential signal, wherein the compensation circuit comprises an amplifier which is connected as a buffer and an integrator, the differential signal and the output signal of the integrator are fed to the input of the buffer amplifier, and wherein the output signal of the buffer amplifier is fed to the inverting input of the integrator and to the input of the controller.

2. The circuit arrangement as claimed in claim 1 , wherein the integrator contains an integration capacitor and switching means to reverse the polarity ot the integration capacitor in synchronism with an oscillator frequency of an oscillator signal, wherein the circuit arrangement is operable to connect, in a one—positive—phase, the one terminal of the integration capacitor to the output of the integrator and the other terminal to the inverting input of the integrator, and in a other—negative—phase, to connect the one terminal to the inverting input and the other terminal to the output of the integrator.

3. The circuit arrangement as claimed in claim 2 , wherein the interference signal and the oscillator signal are generated by means of a single signal source.

4. The circuit arrangement as claimed in claim 1 , wherein the integrator comprises at least two integration capacitors and switching means for reversing a polarity of each of the at least two integration capacitors in synchronism with an oscillator frequency, the circuit arrangement being operable to connect, in identical numbers of phase sections, corresponding to the number of integration capacitors, during a one—positive—phase, the first terminals of the integration capacitors to the output of the integrator and successively the other terminals to the inverting input of the integrator, during a other—negative—phase, to connect the first terminals to the inverting input and successively the other terminals to the output of the integrator.

5. The circuit arrangement as claimed in claim 4 , wherein the interference signal and the oscillator signal are generated by means of a single signal source.

6. A method for compensating interference signals in the control loop of a linear lambda probe comprising the steps of:

forming the difference between a Nernst voltage which is subjected to an interference signal and a reference voltage,

generating a controlling voltage from the difference,

converting the controlling voltage into a pumping current,

generating a compensation signal which is approximated in its curve profile to the interference signal and has an amplitude and frequency which are identical to the interference signal but phase-shifted through 180°, wherein the compensation signal is subtracted from the differential signal and as a result largely cancels out the interference signal, wherein the compensation signal is formed by the steps of:

feeding the difference to a buffer amplifier generating a buffered signal,

integrating the buffered signal and feeding the integrated signal back to said buffer amplifier,

feeding the buffered signal to an input of a controller.

7. A method according to claim 6 , wherein the step of integrating is performed by switching the polarity of a capacitor in the feedback loop of an operational amplifier from a first polarity during a—positive—phase to a second polarity during another—negative—phase.

8. A method according to claim 6 , wherein the step of integrating is performed by reversing a polarity of each of at least two capacitors in the feedback loop of an operational amplifier in synchronism with an oscillator frequency whose phase is divided in identical numbers of positive and negative phase sections corresponding to the number of integration capacitors, wherein the capacitors are sequentially coupled in the feedback loop with a first polarity during sections of a positive phase and are sequentially coupled in the feedback loop with a second polarity during sections of a negative phase.

9. A circuit arrangement for compensating interference signals in the control loop of a linear lambda probe comprising:

an evaluation circuit with a differential amplifier which forms the difference between a Nernst voltage which is subjected to an interference signal and a reference voltage,

a controller generating a controlling voltage from the difference wherein the controlling voltage is converted into a pumping current by a subsequent pumping current source said pumping current being fed back to said linear lambda probe,

a compensation circuit, coupled between the output of the differential amplifier and the input of the controller, for generating a compensation signal which is approximated in its curve profile to the interference signal and has an amplitude and frequency which are identical to the interference signal but phase-shifted through 180°, and for subtracting the compensation signal from the differential signal, wherein the controller is combined with the compensation circuit which contains an amplifier which is connected as an inverter and an integrator, the controller is connected as a summing amplifier to two inputs, the differential signal is fed to the one input of the controller, and wherein the output signal of the controller is fed to the input of the integrator whose output signal is fed to the second input of the controller via the inverter.

10. The circuit arrangement as claimed in claim 9 , wherein the integrator contains an integration capacitor and switching means to reverse the polarity of the integration capacitor in synchronism with an oscillator frequency of an oscillator signal, wherein the circuit arrangement is operable to connect, in a one—positive—phase, the one terminal of the integration capacitor to the output of the integrator and the other terminal to the inverting input of the integrator, and in a other—negative—phase, to connect the one terminal to the inverting input and the other terminal to the output of the integrator.

11. The circuit arrangement as claimed in claim 10 , wherein the interference signal and the oscillator signal are generated by means of a single signal source.

12. The circuit arrangement as claimed in claim 9 , wherein the integrator comprises at least two integration capacitors and switching means for reversing a polarity of each of the at least two integration capacitors in synchronism with an oscillator frequency, the circuit arrangement being operable to connect, in identical numbers of phase sections, corresponding to the number of integration capacitors, during a one—positive—phase, the first terminals of the integration capacitors to the output of the integrator and successively the other terminals to the inverting input of the integrator, during a other—negative—phase, to connect the first terminals to the inverting input and successively the other terminals to the output of the integrator.

13. The circuit arrangement as claimed in claim 12 , wherein the interference signal and the oscillator signal are generated by means of a single signal source.

14. A method for compensating interference signals in the control loop of a linear lambda probe comprising the steps of:

forming the difference between a Nernst voltage which is subjected to an interference signal and a reference voltage,

generating a controlling voltage from the difference,

converting the controlling voltage into a pumping current,

generating a compensation signal which is approximated in its curve profile to the interference signal and has an amplitude and frequency which are identical to the interference signal but phase-shifted through 180°, wherein the compensation signal is subtracted from the differential signal and as a result largely cancels out the interference signal, wherein the controlling voltage is formed by a forming a further difference between said difference and the compensation signal;

and the compensation signal is formed by

integrating the controlling voltage and amplifying the integrated voltage.

15. A method according to claim 14 , wherein the step of integrating is performed by switching the polarity of a capacitor in the feedback loop of an operational amplifier from a first polarity during a—positive—phase to a second polarity during another—negative—phase.

16. A method according to claim 14 , wherein the step of integrating is performed by reversing a polarity of each of at least two capacitors in the feedback loop of an operational amplifier in synchronism with an oscillator frequency whose phase is divided in identical numbers of positive and negative phase sections corresponding to the number of integration capacitors, wherein the capacitors are sequentially coupled in the feedback loop with a first polarity during sections of a positive phase and are sequentially coupled in the feedback loop with a second polarity during sections of a negative phase.