Gas sensor with improved sensitivity and gas sensor component

Abstract

A gas sensor with improved sensitivity. The gas sensor comprises an active sensor unit, a reference sensor unit and a temperature control circuit. The active sensor unit has an active detector. The reference sensor unit has a reference detector. The temperature control circuit is provided and configured to keep a detector at a predetermined temperature.

Claims

1. A gas sensor with improved sensitivity, comprising an active sensor unit with an active detector, an active-sensor heater, and a catalyst, a reference sensor unit with a reference detector and a reference-sensor heater, a temperature control circuit provided and configured to keep the active detector at a constant, predetermined temperature, wherein the temperature control circuit comprises an operational amplifier with an inverted input, a non-inverted input, and an output, and wherein the output of the operational amplifier is electrically coupled directly to the active-sensor heater of the active sensor unit and directly to the reference-sensor heater of the reference sensor unit.

2. The gas sensor of claim 1, wherein the catalyst determines the gas selectivity.

3. The gas sensor of claim 1, wherein the active detector and the reference detector are electrically connected in series.

4. The gas sensor of claim 1, wherein the active-sensor heater of the active sensor and the reference-sensor heater of the reference sensor are electrically connected in parallel.

5. The gas sensor of claim 1, wherein the temperature control circuit provides electrical power to the reference-sensor and the active-sensor heaters.

6. The gas sensor of claim 1, wherein the active detector is thermally coupled to the active-sensor heater of the active sensor unit and the reference detector is thermally coupled to the reference-sensor heater of the reference sensor unit.

7. The gas sensor of claim 1, wherein the inverted input is coupled to a supply voltage and the non-inverted input is coupled to a first node at the output side of the active-sensor heater of the active sensor unit.

8. The gas sensor of claim 1, comprising a signal port having a connection coupled to a second node between the active detector and the reference detector.

9. The gas sensor of claim 8, comprising an evaluation circuit connected to the signal port.

10. The gas sensor of claim 9, wherein the evaluation circuit comprises an application-specific integrated circuit, a microcontroller and/or an analog-to-digital converter.

11. A gas sensor component, comprising the gas sensor of claim 1, wherein the active sensor unit is arranged at a membrane at the top side of a base material, the base material being arranged on or above a carrier substrate comprising a recess.

Description

(1) Working principles and details of preferred embodiments are shown in the accompanying schematic Figures.

(2) In the Figures:

(3) FIG. 1 shows circuit elements of an equivalent circuit diagram of the gas sensor.

(4) FIG. 2 shows the special arrangement of corresponding elements of a gas sensor component in a perspective view.

(5) FIG. 1 shows circuit elements of an equivalent circuit diagram of the gas sensor GS. The gas sensor GS has an active sensor unit ASU and a reference sensor unit RSU. Further, the gas sensor has a temperature control circuit comprising an operational amplifier OPAMP. Further, the gas sensor has a first resistance element R1 and a second resistance element R2 and a third resistance element R3 and a fourth resistance element R4. Further, the gas sensor has an analog-to-digital converter A/D.

(6) The active sensor unit ASU comprises an active detector AD and a heater H. The reference sensor unit RSU comprises a reference detector RD and a heater H. The active detector AD comprises an active element AE, e.g. a catalyst covering at least partially the material of the active detector and being in direct contact with the to-be-monitored atmosphere.

(7) The active detector AD and the reference detector RD are electrically connected in series between a supply potential V.sub.cc and a ground potential. Specifically, the active detector AD is electrically connected between the reference potential V.sub.cc and the second node N2. The reference detector is electrically connected between the second node N2 and the ground potential. Further, the second node N2 is electrically arranged between the active detector AD and the reference detector RD.

(8) The second node N2 is connected to the signal port SP, where an analog output signal of the gas sensor GS is provided. An evaluation circuit EC, e.g. comprising an analog-to-digital converter A/D, can be comprised in the evaluation circuit EC to provide a digital output signal to an external circuit environment.

(9) The heater H of the active sensor unit is formally coupled to the active detector AD and electrically connected between the output of the operational amplifier OPAMP and the ground potential. The heater H of the reference detector RD is also electrically connected between the output of the operational amplifier OPAMP and the ground potential. With respect to the operational amplifier and the ground potential the two heaters are electrically connected in parallel. A feedback signal line electrically connects the output side at the first node N1 of the heater H of the active sensor unit ASU to the non-inverted input of the operational amplifier.

(10) The inverted input of the operational amplifier is electrically connected to a node between the first resistance element R1 and the second resistance element R2, establishing a series connection between the supply potential V.sub.cc and ground. Thus, because the heater H of the active sensor unit ASU can have a temperature-dependent resistance, the heater H of the active sensor unit can be kept at a constant and predetermined temperature. Via the thermal coupling between the heater H of the active sensor unit and the active detector, the active detector can be kept at the constant, predetermined temperature, improving the reliability of the output signal of the gas sensor.

(11) A third resistance element R3 is electrically connected between the first node N1 and the ground potential. A fourth resistance element R4 can be electrically connected between the heater H of the reference sensor unit RSU and the ground potential. The third and the fourth resistance element can be used to determine the ratio of electrical powers provided to the two heaters.

(12) FIG. 2 illustrates a possible physical arrangement of the heater H and of the active detector AD of the active sensor unit ASU of the gas sensor. The heater H and the active detector AD can be arranged on a membrane M. The heater H and/or the active detector AD of the active sensor unit ASU can be covered with the material of the catalyst C. A carrier substrate CS can be provided to carry an insulator I, on which the base B carrying the membrane M is arranged. A recess R provided at the bottom side of the carrier substrate CS together with recesses or holes of the insulator I and of the base B allow the mass of the thermally active elements to be as small as possible, reducing thermal inertia and reducing the response time necessary for a change in the concentration of the to-be-monitored gas.

(13) However, it is possible that the carrier substrate CS, the insulator I and the base B also carry the reference sensor unit with the reference detector and the heater of the reference sensor unit such that a small and compact gas sensor component can be obtained. However, it is preferred that the catalyst only covers one of the two sensor units while the other sensor unit is free from the catalyst.

(14) The gas sensor and the gas sensor component are not limited to the specific details described above and shown in the Figures. The gas sensor can comprise further circuit elements, e.g. for stabilizing the temperature control. The gas sensor component can comprise further elements such as a housing, external contacts, power connections, signal connections and the like.