Circuit arrangement to adjust and calibrate a MEMS-sensor device for flow measurement of gases or liquids

1. Circuitry for the adjustment and calibration of a heating element and an ambient temperature sensor, comprising:

a) an amplifier having a positive input, a negative input, and an output;

b) one or more heating metal oxide semiconductor (MOS) transistors selectably coupled in parallel and having a heating transistor gate, a heating transistor source, and a heating transistor drain, wherein:

1) the heating transistor drain is coupled to the positive input of the amplifier; and

2) the heating transistor source is configured to receive a supply voltage;

3) the heating transistor gate is coupled to the amplifier output;

c) one or more ambient MOS transistors selectably coupled in parallel and having an ambient transistor gate, an ambient transistor source, and an ambient transistor drain, wherein:

1) the ambient transistor gate is coupled to the amplifier output; and

2) the ambient transistor source is configured to receive the supply voltage; and

d) a temperature difference resistance configured:

1) to be coupled at least partially between an ambient connection and the ambient transistor drain; and

2) to be coupled at least partially between the ambient connection and the negative input of the amplifier.

2. The circuitry of claim 1 , wherein the temperature difference resistance comprises a fixed resistor having a first terminal and a second terminal, wherein:

the first terminal is configured to be coupled to the ambient sensor connection; and

the second terminal is coupled to the ambient transistor drain and the negative input of the amplifier.

3. The circuitry of claim 1 , wherein the temperature difference resistance comprises a potentiometer having a first terminal, a second terminal, and a wiper, wherein:

the first terminal is configured to be coupled to the ambient connection;

the second terminal is coupled to the ambient transistor drain; and

the wiper is coupled to the negative input of the amplifier.

4. The circuitry of claim 3 , further comprising:

e) a calibration MOS transistor having a calibration transistor gate, a calibration transistor source, and a calibration transistor drain, wherein:

1) the calibration transistor source is configured to receive the supply voltage;

2) the calibration transistor drain is configured to receive a bias current; and

3) the calibration transistor gate is coupled to the calibration transistor drain; and

f) a selection switch, in the coupling between the amplifier output and the ambient and heating transistor gates, having a first input, a second input, and an output, wherein:

1) the first switch input is coupled to the amplifier output;

2) the second switch input is coupled to the calibration transistor gate; and

3) the switch output is coupled to the ambient transistor gate and the heating transistor gate.

5. The circuitry of claim 4 , further comprises an ambient connection coupled to the first terminal of the potentiometer and configured to be coupled to the ambient temperature sensor, and wherein:

the coupling between the heating transistor drain and the positive input of the amplifier comprises a heating connection configured to be coupled to the heating element; and

the coupling between the wiper and the negative input of the amplifier comprises a reference connection.

6. The circuitry of claim 5 , wherein the potentiometer comprises a digital potentiometer and further comprising a temperature difference digital control coupled to the digital potentiometer and configured to select a desired temperature difference.

7. The circuitry of claim 5 , further comprising a heating digital control coupled to the one or more heating MOS transistors for selectably controlling how many of the one or more heating MOS transistors are actively in parallel.

8. The circuitry of claim 5 , further comprising an ambient digital control coupled to the one or more ambient MOS transistors for selectably controlling how many of the one or more ambient MOS transistors are actively in parallel.

9. The circuitry of claim 5 , further comprising:

a heating digital control coupled to the one or more heating MOS transistors for selectably controlling how many of the one or more heating MOS transistors are actively in parallel; and

an ambient digital control coupled to the one or more ambient MOS transistors for selectably controlling how many of the one or more ambient MOS transistors are actively in parallel.

10. The circuitry of claim 9 , further comprising: a multiplexer coupled to the heating connection, the ambient connection, and the reference connection.

11. A method of adjusting and calibrating a heating element and an ambient temperature sensor, comprising:

selectably coupling a first number of heating MOS transistors in parallel;

selectably coupling a second number of ambient MOS transistors in parallel;

removeably applying a bias current to a collective gate of the first number of heating MOS transistors, thereby creating a first current through a collective drain of the first number of heating MOS transistors;

removeably applying the bias current to a collective gate of the second number of ambient MOS transistors, thereby creating a second current through a collective drain of the second number of ambient MOS transistors;

determining a first voltage caused by the first current passing through the heating element;

determining a second voltage caused by the second current passing through the ambient temperature sensor; and

adjusting the first number of heating MOS transistors and/or the second number of ambient MOS transistors selectably coupled in parallel to substantially minimize a difference between the first voltage and the second voltage.

12. The method of claim 11 , wherein removeably applying the bias current to the collective gates of the first number of heating MOS transistors and the second number of ambient MOS transistors comprises:

switching the collective gates from a control loop amplifier output to a gate of a calibration MOS transistor, wherein the bias current is coupled to a drain of the calibration MOS transistor, and the gate of the calibration MOS transistor is further coupled to the drain of the calibration MOS transistor.

13. The method of claim 11 , wherein:

selectably coupling the first number of heating MOS transistors in parallel comprises digitally controlling individual gate connections for the first number of heating MOS transistors; and

selectably coupling the second number of ambient MOS transistors in parallel comprises digitally controlling individual gate connections for the second number of ambient MOS transistors.

14. The method of claim 11 , further comprising storing the first number of heating MOS transistors and/or the second number of ambient MOS transistors selectably coupled in parallel which substantially minimizes a difference between the first voltage and the second voltage.

15. Circuitry for the adjustment and calibration of a heating element and an ambient temperature sensor, comprising:

a) a heating connection configured to be coupled to the heating element;

b) an ambient connection configured to be coupled to the ambient temperature sensor;

c) a potentiometer having a first terminal, a second terminal, and a wiper, wherein the first terminal is coupled to the ambient connection;

d) a reference connection configured to be coupled to the potentiometer wiper;

e) an amplifier having a positive input, a negative input, and an output, wherein:

1) the negative input is coupled to the reference connection; and

2) the positive input is coupled to the heating connection;

f) one or more heating metal oxide semiconductor (MOS) transistors selectably coupled in parallel and having a heating gate, a heating transistor source, and a heating transistor drain, wherein:

1) the heating transistor drain is coupled to the heating connection; and

2) the heating transistor source is configured to receive a supply voltage;

g) one or more ambient MOS transistors selectably coupled in parallel and having an ambient gate, an ambient transistor source, and an ambient transistor drain, wherein:

1) the ambient transistor drain is coupled to the second terminal of the potentiometer; and

2) the ambient transistor source is configured to receive the supply voltage;

h) a calibration MOS transistor having a calibration gate, a calibration transistor source, and a calibration transistor drain, wherein:

1) the calibration transistor source is configured to receive the supply voltage;

2) the calibration transistor drain is configured to receive a bias current; and

3) the calibration transistor gate is coupled to the calibration transistor drain;

i) a selection switch having a first input, a second input, and an output, wherein:

1) the first switch input is coupled to the amplifier output;

2) the second switch input is coupled to the calibration transistor gate; and

3) the switch output is coupled to the ambient transistor gate and the heating gate.

16. The circuitry of claim 15 , wherein the potentiometer comprises a digital potentiometer and further comprising a temperature difference digital control coupled to the digital potentiometer and configured to select a desired temperature difference.

17. The circuitry of claim 15 , further comprising a heating digital control coupled to the one or more heating MOS transistors for selectably controlling how many of the one or more heating MOS transistors are actively in parallel.

18. The circuitry of claim 15 , further comprising an ambient digital control coupled to the one or more ambient MOS transistors for selectably controlling how many of the one or more ambient MOS transistors are actively in parallel.

19. The circuitry of claim 15 , further comprising:

a heating digital control coupled to the one or more heating MOS transistors for selectably controlling how many of the one or more heating MOS transistors are actively in parallel; and

an ambient digital control coupled to the one or more ambient MOS transistors for selectably controlling how many of the one or more ambient MOS transistors are actively in parallel.

20. The circuitry of claim 19 , further comprising: a multiplexer coupled to the heating connection, the ambient connection, and the reference connection.