# US 10,871,404 B2 · Miniaturized thermistor based thermal sensor

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- Number: US 10,871,404 B2
- Document ID: US10871404B2
- Status: Granted
- Kind: B2
- Application number: 15/981,014
- Filed: 2018-05-16
- Published: 2019-11-21
- Granted: 2020-12-22
- Earliest claimed: 2018-05-16
- Assignees: Birad—Research & Development Company Ltd.
- Applicants: Birad—Research & Development Company Ltd.
- Inventors: Anatoli Mordakhay; Joseph Shor
- Web page: https://patentgrep.com/patent/US10871404B2

## CPC

- G01K 7/226: {using microstructures, e.g. silicon spreading resistance}
- G01K 7/34: using capacitative elements (capacitors per se H01G)
- H10W 40/00: Arrangements for thermal protection or thermal control (integrated devices comprising arrangements for thermal protection H10D89/60)
- G01K: MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR (radiation pyrometry G01J5/00)
- H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10

## Abstract

A thermal sensor includes a first resistor and a first capacitor. The first resistor is a thermistor. A first current source is coupled to the first resistor and the first capacitor. The first current source alternately charges the first resistor and the first capacitor each to a reference voltage, Vtherm. An output of the thermal sensor is a function of a resistance-capacitance (RC) time constant of the first resistor and the first capacitor.

## Claims

### Claim 1

A thermal sensor comprising:
a first resistor and a first capacitor, said first resistor being a thermistor;
a first current source coupled to said first resistor and said first capacitor that alternately charges said first resistor and said first capacitor each to a reference voltage, Vtherm, and wherein an output of said thermal sensor is a function of a resistance-capacitance (RC) time constant of said first resistor and said first capacitor;
two non-overlapping phases, a thermal signal generation phase Φ1 and a counting phase Φ2, wherein in the thermal signal generation phase Φ1, said first current source charges said first resistor to reference voltage Vtherm and discharges said first capacitor to ground, while in the counting phase Φ2, said first current source charge said first capacitor to Vtherm; and
wherein said first current source is coupled to a first clocked switch S1 clocked with a clock signal having the thermal signal generation phase Φ1, and to a second clocked switch S2 clocked with a clock signal having the counting phase Φ2, and to a positive input Vin+ of an amplifier A1, and wherein the first clocked switch S1 is coupled to said first resistor which is grounded and wherein said second clocked switch S2 is coupled to said first capacitor which is grounded, and wherein a third clocked switch S3 clocked with a clock signal having the thermal signal generation phase phase Φ1 is coupled in parallel to said first capacitor, and wherein a negative input Vin− of said amplifier A1 is coupled to a node n1, which is coupled to a second capacitor and to a fourth clocked switch S4, clocked with a clock signal having the thermal signal generation phase Φ1, and which is coupled to an output of said amplifier A1, which outputs to a counter.

### Claim 2 (depends on 1)

The thermal sensor according to claim 1, wherein said thermal signal generation phase Φ1 and said counting phase Φ2 are non-overlapping phases.

### Claim 3 (depends on 1)

The thermal sensor according to claim 1, wherein a time it takes to charge said first resistor and said first capacitor to Vtherm is proportional to temperature.

### Claim 4 (depends on 1)

The thermal sensor according to claim 1, further comprising a comparator, wherein in the thermal signal generation phase Φ1, voltage on said first resistor is stored on said second capacitor and in the counting phase Φ2, voltages on said first and second capacitors are input to first and second inputs of said comparator, respectively, which trips when the voltages on said first and second capacitors are equal, such that time it takes to trip is proportional to temperature measure by said thermal sensor.

### Claim 5 (depends on 4)

The thermal sensor according to claim 4, wherein in the thermal signal generation phase Φ1, aid comparator receives Vtherm at said first input and is connected as a unity gain buffer with its output and said second input connected to each other and to said second capacitor, and wherein in the counting phase Φ2, the output of said comparator is disconnected from said second input and said second capacitor.

### Claim 6 (depends on 5)

The thermal sensor according to claim 5, further comprising a feedback loop which receives Vtherm in the thermal signal generation phase Φ1 and controls the current in said first current source.

### Claim 7 (depends on 6)

The thermal sensor according to claim 6, wherein said first current source is a PMOS transistor whose source is coupled to a positive supply, and wherein an input to said feedback loop is a gate of an NMOS transistor which produces a second current which is mirrored into a first port of a second resistor, said first port of the second resistor being coupled to a gate of the first current source.

### Claim 8 (depends on 7)

The thermal sensor according to claim 7, wherein said comparator comprises two biases and a differential pair, a static bias generated by a third current source and a dynamic bias generated by a fourth current source, wherein the static bias is conducting in both the thermal signal generation phase and the counting phase and the dynamic bias in conducting only in the counting phase, wherein the output of the two biases are coupled to each other and provide current to the differential pair.

### Claim 9 (depends on 8)

The thermal sensor according to claim 8, wherein the third and fourth current sources are NMOS transistors and the fourth current source is coupled to an NMOS transistor which is connected to the first input of said comparator.

### Claim 10 (depends on 1)

The thermal sensor according to claim 1, wherein the first current source comprises a fifth current source and a sixth current source wherein the fifth current source is a multiple of the sixth current source, and the fifth current source charges the first resistor in the thermal signal generation phase and the sixth current source charges the first capacitor in the counting phase.