Ratiometric sensor output topology and methods

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Quick Facts

Patent No.: US 10,908,230
App. No.: 16/901,103
Filed: Jun 15, 2020
Granted: Feb 2, 2021
Kind: B2
Examiner: MAINI, RAHUL
Art Unit: 2866
USPC: 324/244

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Abstract

A sensor includes an output circuit configured to generate a sensor output signal based on an input signal having a logic high or low level, as may be provided by a Schmitt trigger circuit. During normal operation, the output switches between a first percentage of the supply voltage for logic high and a second percentage of the supply voltage for logic low. To convey a failure at the output, an output signal is output as either ground or the supply voltage when a fault is detected. As such, a fault can be communicated any time the output voltage is not equal to the first percentage or the second percentage of the supply voltage.

Claims (41)

1. A circuit to generate an output signal at an output coupled to a supply voltage through a pull-up resistor, the output signal generated in response to an input signal having a logic high level or a logic low level, the circuit comprising:

a resistor divider coupled to the supply voltage and configured to produce a first reference voltage that is a first percentage of the supply voltage or a second reference voltage that is a second percentage of the supply voltage not equal to the first percentage of the supply voltage;

an operational amplifier having a first, feedback input coupled to receive the output signal, a second input selectively coupled to receive the first reference voltage when the input signal is at a logic high level or the second reference voltage when the input signal is at a logic low level, and an output at which a difference signal indicative of a difference between the output signal and the first reference voltage or the second reference voltage is provided; and

2. The circuit of claim 1 , further comprising a switch coupled between the second input of the operational amplifier and the resistor divider, the switch configured to couple a first reference resistor of the resistor divider to the second input of the operational amplifier when the input signal is at the logic high level and to couple a second reference resistor of the resistor divider to the second input of the operational amplifier when the input signal is at the logic low level.

3. The circuit of claim 1 , wherein a fault is indicated when the output signal is at a level corresponding to the supply voltage or ground.

4. The circuit of claim 1 , wherein the pass element comprises an NMOS (n-channel metal-oxide-semiconductor) field-effect transistor.

5. The circuit of claim 1 , further comprising a chopper circuit coupled to the operational amplifier to remove offset associated with the operational amplifier.

6. The circuit of claim 1 , wherein the input signal is provided by a Schmitt trigger circuit.

7. The circuit of claim 6 , wherein the circuit forms part of a magnetic field sensor and wherein the Schmitt trigger circuit generates the input signal by comparing a magnetic field signal to a threshold.

8. The circuit of claim 1 , wherein the circuit forms part of a magnetic field sensor and wherein the input signal is provided by a linear signal path that generates a magnetic field signal indicative of a magnetic field strength.

9. The circuit of claim 1 , further comprising a compensation resistor and a compensation capacitor coupled between the output of the operational amplifier and the second input of the operational amplifier.

10. The circuit of claim 1 , wherein the circuit comprises an integrated circuit and wherein the output signal is provided at an output terminal of the integrated circuit.

11. The circuit of claim 1 , wherein the first percentage of the supply voltage is neither zero percent nor one-hundred percent and wherein the second percentage of the supply voltage is neither zero percent nor one-hundred percent.

12. The circuit of claim 1 , further comprising a switching element coupled in parallel with the pass element and configured to be active when the pass element is not active.

13. A method of generating an output signal at an output of a circuit that receives an input signal having a logic high level or a logic low level, the method comprising:

receiving a supply voltage;

providing the output signal at a first level corresponding to a first percentage of the supply voltage when the input signal is a logic low level by generating a first difference signal by comparing a feedback version of the output signal to a first reference voltage corresponding to the first percentage and controlling a pass element based on the first difference signal;

providing the output signal at a second level corresponding to a second percentage of the supply voltage when the input signal is a logic high level by generating a second difference signal by comparing the feedback version of the output signal to a second reference voltage corresponding to the second percentage and controlling the pass element based on the second difference signal; and

providing the output signal at a third level that is different than the first level and the second level when a fault is detected, wherein the third level corresponds to the supply voltage or ground.

14. The method of claim 13 wherein the input signal is provided by a Schmitt trigger circuit.

15. The method of claim 14 , wherein the circuit forms part of a magnetic field sensor and wherein the Schmitt trigger circuit generates the input signal by comparing a magnetic field signal to a threshold.

16. The method of claim 13 , wherein the first percentage of the supply voltage level is neither zero percent nor one-hundred percent and wherein the second percentage of the supply voltage level is neither zero percent nor one-hundred percent.

17. A circuit to generate an output signal in response to an input signal having a logic high level or a logic low level, the circuit comprising:

a resistor divider coupled to a supply voltage and configured to produce a first reference voltage that is a first percentage of the supply voltage or a second reference voltage that is a second percentage of the supply voltage not equal to the first percentage of the supply voltage;

means responsive to the difference signal to generate the output signal at a level corresponding to the first reference voltage or the second reference voltage, wherein the input signal is provided by a Schmitt trigger circuit and the circuit forms part of a magnetic field sensor and wherein the Schmitt trigger circuit generates the input signal by comparing a magnetic field signal to a threshold.

18. The circuit of claim 17 , further comprising means for indicating a fault when the output signal is at a level corresponding to the supply voltage or ground.

19. A circuit to generate an output signal in response to an input signal having a logic high level or a logic low level, the circuit comprising:

a pass element having a first terminal at which the output signal is provided, a second terminal, and a third, control terminal responsive to the difference signal to generate the output signal at a level corresponding to the first reference voltage or the second reference voltage, wherein the input signal is provided by a Schmitt trigger circuit and wherein the circuit forms part of a magnetic field sensor and wherein the Schmitt trigger circuit generates the input signal by comparing a magnetic field signal to a threshold.

20. A circuit to generate an output signal in response to an input signal having a logic high level or a logic low level, the circuit comprising:

a pass element having a first terminal at which the output signal is provided, a second terminal, and a third, control terminal responsive to the difference signal to generate the output signal at a level corresponding to the first reference voltage or the second reference voltage, wherein the circuit forms part of a magnetic field sensor and wherein the input signal is provided by a linear signal path that generates a magnetic field signal indicative of a magnetic field strength.

21. A circuit to generate an output signal in response to an input signal having a logic high level or a logic low level, the circuit comprising:

a switching element coupled in parallel with the pass element and configured to be active when the pass element is not active.