US-12618920-B2 - Ratiometric sensor circuit

Abstract

The present disclosure relates to a sensor circuit including a control circuit configured to control a constant first signal to a ratiometric second signal using a first amplifier adjustable by an actuating signal, and an adjustable second amplifier for a sensor signal, the gain of which is adjustable by the actuating signal.

Inventors

• Edwin Mario MOTZ

Assignees

• INFINEON TECHNOLOGIES AG

Dates

Publication Date

20260505

Application Date

20221011

Priority Date

20211029

Claims (20)

1. 1 . A sensor circuit, comprising: a first voltage divider configured to provide a constant first signal as a first differential signal based on a constant voltage source, the first differential signal comprising a first pair of signals representative of a constant first voltage difference; a second voltage divider configured to provide a ratiometric second signal as a second differential signal based on an external supply, the second differential signal comprising a second pair of signals representative of a second voltage difference; a control circuit including a first amplifier, the control circuit configured to control a ratio of the constant first signal to the ratiometric second signal using a differential output of the first amplifier, a first gain of the first amplifier being adjustable by an actuating signal that is different from the constant first signal, the first amplifier comprising a first Metal Oxide Semiconductor (MOS) differential stage that includes a first Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and a second MOSFET, wherein a first current source is coupled to integrated source terminals of the first MOSFET and the second MOSFET of the first MOS differential stage; and an adjustable second amplifier for amplifying a sensor signal, the adjustable second amplifier including a second MOS differential stage corresponding to the first MOS differential stage, and a second gain of the adjustable second amplifier being adjustable by the actuating signal, wherein a second current source is coupled to integrated source terminals of a first MOSFET and a second MOSFET of the second MOS differential stage, wherein the control circuit is configured to: generate the actuating signal based on the ratio, adjust the actuating signal in response to a change in the ratio, and control, based on a current value of the actuating signal, the first current source to adjust source currents of the first MOSFET and the second MOSFET of the first MOS differential stage in order to adjust the first gain, and control, based on the current value of the actuating signal, the second current source to adjust source currents of the first MOSFET and the second MOSFET of the second MOS differential stage in order to adjust the second gain.
2. 2 . The sensor circuit as claimed in claim 1 , wherein the sensor circuit is configured to receive a supply signal from the external supply, and wherein the first gain of the first amplifier and the second gain of the adjustable second amplifier have a same ratiometric gain that is linearly dependent on the supply signal.
3. 3 . The sensor circuit as claimed in claim 1 , wherein the sensor circuit is an integrated sensor circuit and the first amplifier and the adjustable second amplifier have substantially identical circuit structures that are formed on a common semiconductor substrate of the integrated sensor circuit.
4. 4 . The sensor circuit as claimed in claim 1 , further comprising: a sensor, configured for outputting the sensor signal in response to a physical measurement variable, wherein the sensor is configured to be supplied by a supply signal from the external supply such that the sensor signal is linearly dependent on the supply signal.
5. 5 . The sensor circuit as claimed in claim 1 , further comprising the constant voltage source, wherein the constant voltage source is a reference voltage source configured to provide a reference voltage as the constant first signal.
6. 6 . The sensor circuit as claimed in claim 5 , wherein the reference voltage source comprises a bandgap reference.
7. 7 . The sensor circuit as claimed in claim 5 , wherein the sensor circuit is configured to receive a supply signal from an external supply, wherein the reference voltage source and a sensor that provides the sensor signal are supplied by the supply signal, and the ratiometric second signal is linearly dependent on the supply signal.
8. 8 . The sensor circuit as claimed in claim 1 , wherein the first voltage divider is configured to be connected between an external supply voltage of the external supply and a ground, and configured to provide a ratiometric voltage as the ratiometric second signal.
9. 9 . The sensor circuit as claimed in claim 1 , wherein the control circuit comprises a transconductance amplifier having a first input for the constant first signal amplified using the first amplifier and a second input for the ratiometric second signal, and wherein the transconductance amplifier is configured to output the actuating signal at an output of the transconductance amplifier based on a difference between the constant first signal and the ratiometric second signal.
10. 10 . The sensor circuit as claimed in claim 1 , wherein the first amplifier is configured to generate an amplifier output signal based on the constant first signal, and the control circuit is configured to generate the actuating signal based on a difference between the amplifier output signal and the ratiometric second signal.
11. 11 . The sensor circuit as claimed in claim 10 , wherein the control circuit is configured to generate the actuating signal to drive the difference between the amplifier output signal and the ratiometric second signal to substantially zero.
12. 12 . The sensor circuit as claimed in claim 10 , wherein the control circuit is configured to control the first current source and the second current source based on the current value of the actuating signal to drive the difference between the amplifier output signal and the ratiometric second signal to substantially zero.
13. 13 . The sensor circuit as claimed in claim 10 , wherein the first amplifier is a first differential amplifier, wherein the adjustable second amplifier is a second differential amplifier, and wherein the amplifier output signal is a differential output signal comprising a pair of output signals.
14. 14 . The sensor circuit as claimed in claim 13 , further comprising: a transconductance amplifier configured to receive the amplifier output signal at a first differential input and the second differential signal at a second differential input, and generate the actuating signal.
15. 15 . The sensor circuit as claimed in claim 1 , wherein the sensor circuit is configured to receive a supply signal from an external supply, and wherein the sensor signal is linearly dependent on a supply signal.
16. 16 . The sensor circuit as claimed in claim 1 , wherein the control circuit comprises a transconductance amplifier comprising: a first differential input configured to receive the differential output from the first amplifier, the differential output comprising a pair of output signals; a second differential input configured to receive the second pair of signals of the ratiometric second signal; and an output configured to output the actuating signal, and wherein the transconductance amplifier is configured to generate and adjust the actuating signal based on a difference between the differential output and the ratiometric second signal.
17. 17 . The sensor circuit as claimed in claim 16 , wherein the differential output is dependent on the constant first signal.
18. 18 . The sensor circuit as claimed in claim 16 , wherein the first amplifier is configured to receive the constant first signal, and generate the differential output based on the constant first signal.
19. 19 . The sensor circuit as claimed in claim 18 , wherein the first pair of signals includes a first signal and a second signal, wherein the first MOSFET of the first MOS differential stage includes a first gate configured to receive the first signal, and wherein the second MOSFET of the first MOS differential stage includes a second gate configured to receive the second signal.
20. 20 . A method for operating a sensor circuit, comprising providing, by a first voltage divider, a constant first signal as a first differential signal based on a constant voltage source, the first differential signal comprising a first pair of signals representative of a constant first voltage difference; providing, by a second voltage divider, a ratiometric second signal as a second differential signal based on an external supply, the second differential signal comprising a second pair of signals representative of a second voltage difference; controlling, by a control circuit, a ratio of the constant first signal to the ratiometric second signal using a differential output of a first amplifier of the control circuit, a first gain of the first amplifier being adjustable by an actuating signal that is different from the constant first signal, the first amplifier comprising a first Metal Oxide Semiconductor (MOS) differential stage that includes a first Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and a second MOSFET, wherein a first current source is coupled to integrated source terminals of the first MOSFET and the second MOSFET of the first MOS differential stage; generating, by the control circuit, the actuating signal based on the ratio; adjusting, by the control circuit, the actuating signal in response to a change in the ratio; adjusting the first gain of the first amplifier by controlling, based on an adjustment to the actuating signal, the first current source to adjust source currents of the first MOSFET and the second MOSFET of the first MOS differential stage; and adjusting a second gain of an adjustable second amplifier based on the adjustment to the actuating signal, the adjustable second amplifier being configured to amplify a sensor signal, the adjustable second amplifier including a second MOS differential stage corresponding to the first MOS differential stage, wherein a second current source is coupled to integrated source terminals of a first MOSFET and a second MOSFET of the second MOS differential stage, and wherein adjusting the second gain of the adjustable second amplifier includes controlling, based on the adjustment to the actuating signal, the second current source to adjust source currents of the first MOSFET and the second MOSFET of the second MOS differential stage.

Description

CROSS REFERENCE TO RELATED APPLICATION This application claims priority to German Patent Application No. 102021128249.7 filed on Oct. 29, 2021, the content of which is incorporated by reference herein in its entirety. TECHNICAL FIELD The present disclosure relates generally to a sensor circuit and in particular to sensor circuits having a ratiometric behavior. BACKGROUND In electronics the term “ratiometric” means that an unknown variable can be derived from a known ratio of a plurality of other variables to one another. Generally, during a ratiometric measurement as a quotient to two variables with the same superposed disturbance, it turns out that the latter does not influence the measurement. A ratiometric measurement variable (such as e.g. a measured magnetic field strength) is for example independent of a supply voltage (VDD) that may be subject to fluctuations. If the supply voltage rises unexpectedly at a measurement system, for example, a measurement signal coupled linearly to the supply voltage thus rises concomitantly. The variable to be measured has not changed, however. If the measurement signal were then passed to an ADC (Analog-to-converter) with a fixed reference voltage, the result would be that the ADC supplies a code that corresponds to a higher measurement variable—incorrect measurement—not a ratiometric system in this case. If the reference voltage of the ADC also concomitantly rose linearly with respect to the supply, the variable to be measured would not change at the output of the ADC—correct measurement—since a ratiometric system is present in this case. Ratiometric therefore means that if the measured signal changes as a result of a disturbance variable in the system, then the comparison variable must change in the same way, such that the change as it were “cancels out” and the change remains with “1/1”. The measurement signal is then multiplied by this fraction. The ratiometric is perfect with 1, already poorer with 1.15, etc. Sensor circuits having a fully ratiometric output (ratiometric sensor circuits) can be realized using digital signal processing, for example, but are relatively more expensive and slow. Ratiometric sensor circuits can for example also be realized using digitally assisted amplifiers having a digitally controlled gain. These do not have a problem with regard to speed, but are even more expensive. Sensors having a ratiometric quiescent voltage but a fixed sensitivity (=gain) avoid an analog multiplication by the supply voltage, but do not offer the functionality of a mechanical potentiometer and are not appropriate for a low-cost microprocessor (which receives the sensor signal) which uses the supply voltage as ADC reference (ADC=analog-to-digital converter). A sensor having a fixed sensitivity (gain) does not offer a complete ratiometric reaction. Therefore, there is a need for improved ratiometric sensor circuits with at the same time manageable costs. SUMMARY This need is met by circuits and methods as claimed in the independent claims. The dependent claims relate to advantageous developments. In accordance with a first aspect of the present disclosure, a sensor circuit is proposed which has a control circuit configured to control a constant first signal (e.g. constant current or constant voltage) to a ratiometric second signal (e.g. ratiometric current or ratiometric voltage) using a first amplifier adjustable by an actuating or control signal. The second signal is thus linearly coupled to a supply signal (e.g. supply voltage). The sensor circuit includes an adjustable second amplifier for a sensor signal, the gain of which is adjustable by the control signal of the control circuit. As a result, a ratiometric gain can be obtained at the second amplifier for the sensor signal. As a result, the gain of the second amplifier is likewise linearly coupled to the supply signal (e.g. supply voltage). With the proposed circuit arrangement, a ratiometric behavior can be attained with relatively simple and cost-effective amplifier designs. In accordance with some example implementations, the first and second amplifiers are configured as replica amplifiers, e.g. as copies of one another. If for example the second amplifier for the sensor signal is regarded as the main amplifier, then the first amplifier can be configured as an exact copy of the main amplifier. However, the first amplifier of the control circuit does not amplify the sensor signal, but rather serves for adjusting the control signal for the (structurally identical) second amplifier. The term “amplifier” here does not necessarily mean just a single amplifier element (such as e.g. a transistor), but rather can mean a complete amplifier circuit which can have a plurality of circuit components, such as e.g. bipolar or MOS differential stages, cascodes, etc. The purpose behind using a replica amplifier may be that both amplifiers always behave identically even under varying ambient conditions. “Replica amplifie