1. A subtractor circuit comprising:
a first signal input to receive a first signal;
a first signal path coupled to the first signal input;
a second signal input to receive a second signal;
a second signal path coupled to the second signal input; and
an operational amplifier comprising:
a first input coupled to the first signal path to receive the first signal;
a second input coupled to the second signal path to receive the second signal;
a first output that provides a subtractor signal output that is a function of a difference between the first signal and the second signal; and
a second output connected to the first input via a feedback path that provides the subtractor signal output as a feedback signal to the first input.
2. The circuit of claim 1, wherein the feedback path comprises a direct connection from the second output to the first input as a current feedback path.
3. The circuit of claim 1, further comprising a cascade circuit coupled to the first output of the operational amplifier that receives the subtractor signal output.
4. The circuit of claim 1, further comprising a power detector having an input that receives a radio-frequency signal and having an output coupled to the first signal input that provides the first signal dependent on a power level of the radio-frequency signal.
5. The circuit of claim 4, further comprising a second power detector having an output coupled to the second signal input that provides the second signal as a reference signal having a constant level.
6. The circuit of claim 5, wherein the first signal path comprises a first resistor and a second resistor, connected in series and having substantially equal resistance.
7. The circuit of claim 1, wherein the feedback path comprises a current-controlled voltage source.
8. The circuit of claim 7, wherein the current-controlled voltage sources comprises a resistor.
9. The circuit of claim 1, wherein the feedback path comprises a current mirror and a current-controlled voltage source, wherein the current-controlled voltage source is connected to the first output of the operational amplifier via the current mirror.
10. A subtractor circuit comprising:
a first power detector to receive a radio frequency signal and generate a first signal having a first voltage level according to a power level of the radio frequency signal;
a second power detector to generate a second signal having a constant voltage level according to a ground reference value; and
a power amplifier comprising:
a first input to receive the first signal and a feedback signal;
a second input to receive the second signal;
a first output to generate the feedback signal according to the first signal and the second signal; and
a second output to generate a differential output signal according to the first signal and the second signal.
11. The circuit of claim 10, wherein the first voltage level is about 0.5 to 2 volts.
12. The circuit of claim 11, wherein the constant voltage level is about 0.5 and a differential voltage of the first signal and the second signal is about 0.0 to 1.5 volts.
13. The circuit of claim 10, wherein the feedback signal has a current value proportional to a differential voltage of the first signal and the second signal.
14. The circuit of claim 10, wherein the differential output signal has a current proportional to a differential voltage of the first signal and the second signal.
15. The circuit of claim 14, further comprising a current conversion circuit to receive the differential output signal and convert the differential output signal into an output voltage signal, wherein the output voltage signal has a voltage level proportional to the differential voltage of the first signal and the second signal.
16. The circuit of claim 10, wherein the feedback signal and the differential output signal are as synchronous signal sources.
17. The circuit of claim 10, wherein the feedback signal has a constant voltage level and the differential output signal has a varying voltage level.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A sensor element comprising a contamination-resistant coating on at least a portion thereof, the coating comprising gamma alumina and magnesium titanate.
2. The element of claim 1, wherein the coating has a thickness of about 50 to about 300 microns.
3. The element of claim 1, wherein the coating has a porosity of about 10 to about 55 percent.
4. The element of claim 1, wherein the portion of the sensor element is a substrate having a plurality of edges, and wherein the coating does not touch or cover at least one of the edges.
5. The element of claim 4, wherein the substrate is a surface of an electrolyte foil, and the surface has an exposed portion that is not covered by the coating.
6. The element of claim 5, wherein the coating at least partially covers an electrode.
7. The element of claim 1, wherein the portion of the sensor element is a protective layer comprising at least one of zirconium oxide, aluminum oxide, titanium oxide, magnesium oxide, and a combination thereof.
8. The element of claim 1, wherein the coating further comprises boehmite alumina.
9. The element of claim 8, wherein the coating has a thickness of about 50 to about 300 microns.
10. A sensor element comprising a contamination-resistant coating on at least a portion thereof, the coating comprising gamma alumina, magnesium titanate, and boehmite alumina.
11. A method of making a contamination-resistant sensor element:
mixing gamma alumina and magnesium titanate to form a mixture;
applying the mixture to at least a portion of a sensor element; and
temperature treating the mixture to form a contamination-resistant coating on the sensor element.
12. The method of claim 11, wherein the mixture further comprises boehmite alumina.
13. The method of claim 12, wherein the mixture comprises about 20 to about 40 percent by weight gamma alumina, about 0.01 to about 8 percent by weight magnesium titanate, and about 1 to about 20 percent by weight boehmite alumina.
14. The method of claim 12, wherein the mixture further comprises a low temperature binder.
15. The method of claim 14, wherein the low-temperature binder comprises at least one of hydroxyethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetate, polyacrylic resins, and a combination thereof.
16. The method of claim 14, wherein the low temperature binder comprises polyvinyl alcohol.
17. The method of claim 14, wherein the mixture comprises about 20 to about 40 percent by weight gamma alumina, about 0.01 to about 8 percent by weight magnesium titanate, about 1 to about 20 percent by weight boehmite alumina, and about 0.5 to about 10 percent by weight low temperature binder.
18. The method of claim 17, wherein the contamination-resistant coating has a thickness of about 50 to about 300 microns and a porosity of about 10 to about 55 percent.
19. The method of claim 12, wherein the portion of the element is a substrate having a plurality of edges, and the coating does not touch or cover at least one of the edges.
20. The method of claim 19, wherein the substrate is a surface of an electrolyte foil, and the surface has an exposed portion that is not covered by the coating.
21. The method of claim 20, wherein an adhesive is used to secure the coating to the substrate, and the adhesive adheres to at least a portion of the exposed portion and at least a portion of the coating.
22. The method of claim 21, wherein the electrolyte foil has a side, and the adhesive adheres to at least a portion of the side.
23. The method of claim 22, further comprising a protective layer comprising at least one of zirconium oxide, aluminum oxide, titanium oxide, magnesium oxide, and a combination thereof, the protective layer being positioned between the coating and the foil.
24. The method of claim 12, wherein the portion of the sensor element is a protective layer.
25. The method of claim 24, wherein the protective layer is mechanically structured to improve adhesion between the coating and the sensor element.
26. The method of claim 25, wherein the protective layer comprises at least one of zirconium oxide, aluminum oxide, titanium oxide, magnesium oxide, and a combination thereof.
27. The method of claim 12, wherein the sensor element is a part of an automotive exhaust gas sensor.
28. The method of claim 11, wherein the mixture is temperature-treated by drying the mixture at room temperature for at least about 10 minutes and then heating the mixture in the range of about 250\xb0 C. to about 1200\xb0 C. for about 30 minutes to about 8 hours.
29. A sensor element comprising:
a substrate having a plurality of edges;
a contamination-resistant coating comprising gamma alumina and magnesium titanate applied to at least a portion of the substrate such that the coating does not touch or cover at least one of the edges, thereby leaving an exposed part of the substrate not covered by the coating; and
an adhesive adhering to at least a portion of the exposed part and at least a portion of the coating to secure the coating to the substrate.