Hall sensor trim circuit

1. A Hall sensor trim circuit, comprising:

a current source;

a transistor comprising:

a first terminal;

a second terminal; and

a third terminal coupled to the current source;

a reference voltage circuit;

an amplifier, comprising:

an output terminal coupled to the first terminal of the transistor;

a first input terminal coupled to the second terminal of the transistor; and

a second input terminal coupled to the reference voltage circuit; and

a Hall sensor coupled to the current source.

2. The Hall sensor trim circuit of claim 1 , wherein:

the reference voltage circuit comprises:

a first reference voltage terminal; and

a second reference voltage terminal; and

the Hall sensor trim circuit further comprises:

a first resistor comprising:

a first terminal coupled to the first reference voltage terminal; and

a second terminal coupled to the first input terminal of the amplifier; and

a second resistor comprising:

a first terminal coupled to the second reference voltage terminal; and

a second terminal coupled to the first input terminal of the amplifier.

3. The Hall sensor trim circuit of claim 2 , wherein:

the first resistor is a fixed resistor; and

the second resistor is a variable resistor.

4. The Hall sensor trim circuit of claim 3 , wherein the variable resistor comprises an R-2R resistor ladder network.

5. The Hall sensor trim circuit of claim 1 , wherein the reference voltage circuit comprises:

a first reference voltage terminal;

a second reference voltage terminal;

a first resistor comprising:

a first terminal coupled to the first reference voltage terminal; and

a second terminal coupled to the second input terminal of the amplifier; and

a second resistor comprising:

a first terminal coupled to the second reference voltage terminal; and

a second terminal coupled to the second input terminal of the amplifier.

6. The Hall sensor trim circuit of claim 5 , wherein:

the amplifier is a first amplifier; and

the Hall sensor trim circuit comprises:

a second amplifier comprising:

an input terminal coupled to the second terminal of the first resistor and the second terminal of the second resistor; and

an output terminal coupled to the second input terminal of the first amplifier.

7. The Hall sensor trim circuit of claim 5 , wherein:

the amplifier is a first amplifier; and

the reference voltage circuit comprises:

a second amplifier comprising:

a first output terminal coupled to the first reference voltage terminal;

a second output terminal coupled to the second reference voltage terminal; and

a third output terminal coupled to the second input terminal of the first amplifier.

8. The Hall sensor trim circuit of claim 7 , wherein:

the second amplifier comprises:

a first input terminal; and

a second input terminal; and

the reference voltage circuit comprises:

a first variable resistor comprising:

a first terminal coupled to a power supply terminal; and

a second terminal coupled to the first input terminal of the second amplifier;

a second variable resistor comprising:

a first terminal coupled to a ground terminal; and

a second terminal coupled to the second input terminal of the second amplifier;

a first fixed resistor comprising:

a first terminal coupled to the first output terminal of the second amplifier; and

a second terminal coupled to the first input terminal of the second amplifier;

a second fixed resistor comprising:

a first terminal coupled to the second output terminal of the second amplifier; and

a second terminal coupled to the second input terminal of the second amplifier.

9. A Hall sensor trim circuit, comprising:

a current source;

a Hall sensor coupled to the current source;

a reference voltage circuit;

a voltage divider circuit;

a transistor configured to pass a bias current generated by the current source; and

an amplifier coupled to the voltage divider circuit, the voltage reference circuit, and the transistor, and configured to drive the transistor based on output of the voltage divider circuit, output of the reference voltage circuit, and feedback from the transistor.

10. The Hall sensor trim circuit of claim 9 , wherein the voltage divider circuit comprises:

a first resistor with a first temperature coefficient; and

a second resistor with a second temperature coefficient;

wherein the first temperature coefficient is different from the second temperature coefficient.

11. The Hall sensor trim circuit of claim 10 , wherein:

the first resistor is a fixed resistor; and

the second resistor is a variable resistor.

12. The Hall sensor trim circuit of claim 11 , wherein the variable resistor comprises a digital-to-analog converter.

13. The Hall sensor trim circuit of claim 9 , wherein the voltage reference circuit comprises a first fixed resistor and a second fixed resistor configured as a voltage divider.

14. The Hall sensor trim circuit of claim 9 , wherein:

the amplifier is a first amplifier; and

the voltage reference circuit comprises a second amplifier configured to buffer output of the voltage divider circuit to the first amplifier.

15. The Hall sensor trim circuit of claim 9 , wherein:

the amplifier is a first amplifier; and

the voltage reference circuit comprises:

a second amplifier configured to:

generate a positive reference voltage for application to the voltage divider circuit;

generate a negative reference voltage for application to the voltage divider circuit; and

generate a common mode voltage for input to the first amplifier.

16. The Hall sensor trim circuit of claim 15 , wherein:

the second amplifier comprises:

a non-inverting input terminal; and

an inverting input terminal; and

the voltage reference circuit comprises:

a first variable resistor configured to drive the non-inverting input terminal; and

a second variable resistor configured to drive the inverting input terminal.

17. A method, comprising:

applying a magnetic field to a Hall sensor;

setting a positive reference voltage and a negative reference voltage to a same voltage; wherein the positive reference voltage and the negative reference voltage control a bias current to the Hall sensor;

setting a most significant bit of a voltage divider control code;

applying the voltage divider control code to an analog-to-digital converter of a voltage divider circuit that controls the bias current to the Hall sensor;

measuring a first output of the Hall sensor;

setting the positive reference voltage and the negative reference voltage to different voltages;

measuring a second output of the Hall sensor;

comparing the first output of the Hall sensor to the second output of the Hall sensor; and

adjusting the voltage divider control code to make the second output of the Hall sensor a same voltage as the first output of the Hall sensor.

18. The method of claim 17 , further comprising storing a value of the voltage divider control code that makes the second output of the Hall sensor the same voltage as the first output of the Hall sensor as a final value of the voltage divider control code.

19. The method of claim 17 , further comprising;

increasing a temperature of the Hall sensor; and

changing a difference of the positive reference voltage and the negative reference voltage to make a third output of the Hall sensor the same voltage as the first output of the Hall sensor.

20. The method of claim 19 , further comprising changing a difference of the positive reference voltage and the negative reference voltage to make a fourth output of the Hall sensor a predetermined voltage, wherein the predetermined voltage corresponds to a predetermined change in output of the Hall sensor over temperature.