# US 2018/0026618 A1 · High-speed continuous-time comparator circuit

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- Number: US 2018/0026618 A1
- Document ID: US20180026618A1
- Status: Published application
- Kind: A1
- Application number: 15/394,472
- Filed: 2016-12-29
- Published: 2018-01-25
- Earliest claimed: 2016-07-21
- Assignees: STMicroelectronics S.r.l.
- Applicants: Stmicroelectronics S.R.L.
- Inventors: Germano Nicollini; Roberto Modaffari
- Web page: https://patentgrep.com/patent/US20180026618A1

## CPC

- H03K 5/2481: {with at least one differential stage}
- G01R 19/0038: {Circuits for comparing several input signals and for indicating the result of this comparison, e.g. equal, different, greater, smaller (comparing pulses or pulse trains according to amplitude)}
- H03F 3/45179: {using MOSFET transistors as the active amplifying circuit (H03F3/45278 takes precedence)}
- H03F 3/45273: {Mirror types}
- H03K 3/0377: {Bistables with hysteresis, e.g. Schmitt trigger (non-regenerative amplitude discriminators G01R19/165)}
- H03K 5/24: the characteristic being amplitude
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- H03F: AMPLIFIERS

## Abstract

A comparator circuit including: a first node and a second node, which receive a first current and a second current, respectively; a first current mirror, which includes a first load transistor and a first output transistor; and a second current mirror, which includes a second load transistor and a second output transistor. The comparator circuit further includes: a first feedback transistor and a second feedback transistor cross-coupled together, the control terminals of the first and second feedback transistors being connected to the first and second nodes, respectively; a first resistor, having a first terminal, which is connected to the control terminal of the first load transistor, and a second terminal, which is connected to the first node and to the control terminal of the first output transistor; and a second resistor, having a first terminal, connected to the control terminal of the second load transistor, and a second terminal, connected to the second node and to the control terminal of the second output transistor.

## Claims

### Claim 1

A continuous-time comparator circuit, comprising:
a first node and a second node configured to receive, respectively, a first current and a second current which form a differential signal;
a first current mirror including a first load transistor having a control terminal and a conduction terminal, and a first output transistor having a respective control terminal, the conduction terminal of the first load transistor being connected to the first node, said first output transistor being configured to be traversed by a first mirrored current that is a function of the first current;
a second current mirror including a second load transistor having a respective control terminal and a respective conduction terminal, and a second output transistor having a respective control terminal, the conduction terminal of the second load transistor being connected to the second node, said second output transistor being configured to be traversed by a second mirrored current that is a function of the second current;
a first feedback transistor having a respective conduction terminal and a respective control terminal, which are connected to said first node and to said second node, respectively;
a second feedback transistor having a respective conduction terminal and a respective control terminal, which are connected to said second node and to said first node, respectively;
output circuitry electrically coupled to the first and second output transistors and configured to generate an output signal that switches between a first value and a second value as a function of said first and second mirrored currents;
a first resistor having a first terminal connected to the control terminal of the first load transistor, and a second terminal connected to the first node and to the control terminal of the first output transistor; and
a second resistor having a respective first terminal connected to the control terminal of the second load transistor, and a respective second terminal connected to the second node and to the control terminal of the second output transistor.

### Claim 2 (depends on 1)

The continuous-time comparator circuit according to claim 1, wherein each one of the first resistor and the second resistor has a resistance greater than or equal to 100 kΩ.

### Claim 3 (depends on 1)

The continuous-time comparator circuit according to claim 1, wherein said output circuitry forms an output node and is configured to vary a voltage present on said output node as a function of the difference between said first and second mirrored currents.

### Claim 4 (depends on 3)

The continuous-time comparator circuit according to claim 3, wherein each of said first and second output transistors has a respective conduction terminal; and wherein said output circuitry comprises a third current mirror electrically coupled to the conduction terminals of the first and second output transistors and to said output node.

### Claim 5 (depends on 3)

The continuous-time comparator circuit according to claim 3 further comprising at least one inverter having an input connected to said output node.

### Claim 6 (depends on 1)

The continuous-time comparator circuit according to claim 1 further comprising a differential pair including a first input transistor and a second input transistor, each of which has a respective conduction terminal and a respective control terminal; and wherein one of the control terminals of the first and second input transistors is configured to be set at a reference voltage, the other terminal being configured to receive an input signal; and wherein the respective conduction terminals of the first and second input transistors are connected to the first and second input nodes, respectively.

### Claim 7 (depends on 1)

The continuous-time comparator circuit according to claim 1, wherein said first and second load transistors, said first and second output transistors, and said first and second feedback transistors are MOSFETs.

### Claim 8

A comparator circuit, comprising:
an input circuit coupled to receive first and second input signals and configured to provide first and second current signals to first and second input nodes, respectively, based on the first and second input signals;
a first current mirror including a first load transistor coupled to the first input node and including a first output transistor configured to generate a first mirrored current based on the first current signal, the first current mirror including a first resistive circuit to set a constant associated with the first load transistor to a first time constant value;
a first feedback transistor including a conduction node coupled to the first input node and a control node coupled to the second input node, a second time constant being associated with the first feedback transistor where the second time constant has a second time constant value that is less than the first time constant value;
a second current mirror including a second load transistor coupled to the second input node and including a second output transistor configured to generate a second mirrored current based on the second current signal, the second current mirror including a second resistive circuit to set a time constant associated with the second load transistor to the first time constant value;
a second feedback transistor including a conduction node coupled to the second input node and a control node coupled to the first input node, the second time constant being associated with the second feedback transistor; and
output circuitry coupled to the first and second output transistors and configured to generate an output signal based on the first and second mirrored currents.

### Claim 9 (depends on 8)

The comparator circuit of claim 8, wherein the input circuit comprises a differential pair of transistors.

### Claim 10 (depends on 8)

The comparator circuit of claim 8, wherein the output circuitry is coupled to an output node and is configured to control a voltage on the output node based on a difference between the first and second mirrored currents.

### Claim 11 (depends on 10)

The comparator circuit of claim 10, wherein the output circuitry comprises a third output transistor in a diode-coupled configuration, the third output transistor coupled to the first output transistor and the output circuitry further including a fourth output transistor coupled to the third output transistor and to the output node.

### Claim 12 (depends on 11)

The comparator circuit of claim 11 further comprising a plurality of series-connected inverters, an input of a first one of the plurality of series-connected inverters coupled to the output node.

### Claim 13 (depends on 8)

The comparator of claim 8, where each of the transistors comprises a MOSFET.

### Claim 14 (depends on 8)

The comparator of claim 8, wherein each of the first and second load transistors has a width-to-length ratio W/L for a channel of the transistor and each of the first and second feedback transistors has a width-to-length ratio for a channel of the transistor, and wherein the width to length ratio for the first and second load transistors is great then the width to length ration for the first and second feedback transistors.

### Claim 15 (depends on 8)

The comparator circuit of claim 8 wherein each of the first and second resistive circuits comprises a resistor having a resistance value that is greater than or equal to approximately 100 kΩ.

### Claim 16

A method of comparing first and second input signals, the method comprising:
providing a first current to a first input node based on the first input signal;
providing a second current to a second input node based on the second input signal;
controlling a voltage on the first input node through a negative-feedback mechanism based upon the first current;
controlling a voltage on the second input node through the negative-feedback mechanism based upon the second current;
controlling the voltage on the first input node through a positive-feedback mechanism based upon the voltage on the second input node;
controlling the voltage on the second input node through the positive-feedback mechanism based on the voltage on the first input node;
generating first and second mirrored current based on the first and second currents, respectively; and
generating an output signal based on the first and second mirrored currents.

### Claim 17 (depends on 16)

The method of claim 16, wherein generating an output signal based on the difference between the first and second mirrored currents.

### Claim 18 (depends on 16)

The method of claim 16, wherein negative-feedback mechanism has an associated first time constant and the positive-feedback mechanism has an associated second time constant, the first time constant being greater than the second time constant.

### Claim 19 (depends on 16)

The method of claim 16, wherein controlling the voltages on the first and second input nodes through the positive-feedback mechanism comprises controlling the voltages through a pair of cross-coupled transistors coupled to the first and second input nodes.

### Claim 20 (depends on 16)

The method of claim 16, wherein controlling the voltages on the first and second input nodes through the negative-feedback mechanism comprises providing the first and second currents to first and second diode-coupled load transistors coupled to the first and second input nodes, respectively.