# US 12,181,610 B2 · CMOS image sensor for direct time of flight measurement

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 12,181,610 B2
- Document ID: US12181610B2
- Status: Granted
- Kind: B2
- Application number: 17/292,581
- Filed: 2019-11-22
- Published: 2021-12-23
- Granted: 2024-12-31
- Earliest claimed: 2018-11-23
- Assignees: Teledyne Innovaciones Microelectronicas Slu
- Applicants: Teledyne Innovaciones Microelectronicas Slu
- Inventors: Rafael Dominguez Castro; José Ángel Segovia De La Torre; Ana Gonzalez Marquez; Rafael Romay; Amanda Jiménez Marrufo
- Web page: https://patentgrep.com/patent/US12181610B2

## CPC

- G01S 7/4863: Detector arrays, e.g. charge-transfer gates
- G01S 7/487: Extracting wanted echo signals {, e.g. pulse detection}
- G01S 7/4876: {by removing unwanted signals (G01S7/495 takes precedence)}
- G01S 17/10: using transmission of interrupted, pulse-modulated waves (determination of distance by phase measurements G01S17/32)
- G01S 17/894: Three-dimensional [3D] imaging with simultaneous measurement of time-of-flight at a two-dimensional [2D] array of receiver pixels, e.g. time-of-flight cameras or flash lidar
- H04N 25/65: applied to reset noise, e.g. KTC noise related to CMOS structures by techniques other than CDS
- H04N 25/77: Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
- H04N 25/78: Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

A direct TOF optic sensor is based on CMOS pixels, wherein a pixel structure comprises a photodetector PhD, a non linear resistance R and a transfer MOS transistor in series, and delivers an output signal at a sensing node SN between the resistor and the transfer transistors. The photogenerated current is continuously drained into the nonlinear resistance and converted to a voltage signal by the RC circuit formed by the nonlinear resistance and a capacitance at the sense node SN. The voltage signal is continuously transmitted to a readout circuitry 300 having a fast analog to digital converter. The RC circuit within the pixel structure has a low pass filtering function and a high frequency integrating function, so that noise, in particular thermal noise due to the nonlinear resistance is mainly shifted in a low frequency range, separate from a high frequency range of the main signal component corresponding to a pulse light signal received at the photodetector. The main signal component is recovered by means of one of a band pass or high pass filter F implemented in the readout circuitry, that increases the signal to noise ratio in the high frequency range.

## Claims

### Claim 1

A CMOS imaging sensor for detecting time occurrence of a light pulse having a given pulse duration T, comprising:
pixels, each pixel having a pixel structure comprising at least:
a photodetector operating as a current source;
a nonlinear resistor, connected and operated continuously between a voltage supplying node of the pixel and a sense node,
wherein the sense node is a capacitive sense node having a capacitance, the nonlinear resistor and capacitance of the sense node configured to operate as a low pass filter and to perform current to voltage conversion in a low frequency range and integration in a high frequency range;
a control circuit for controlling a measurement phase in at least a selected pixel (P) for measuring a time occurrence of a rising edge of a light pulse reaching the photodetector in the pixel, the control circuit being configured to:
implement continuous current to voltage conversion inside the pixel through the nonlinear resistor, and
convert, by the nonlinear resistor and capacitance, the signal received from the photodetector to produce a voltage signal at the sense node that has a main signal component comprising at least a rising edge pulse location information in the high frequency range, and a noise component mainly concentrated in the low frequency range spaced apart from said high frequency range, and
a readout circuitry of a voltage signal from the sense node of a selected pixel, which comprises at least:
an analog to digital converter applying a high sampling time in respect of the pulse width duration; and
a filter (F) configured to apply continuously at least one of a band pass or high pass filter, before or after analog to digital conversion, having the effect of increasing the signal to noise ratio in at least a frequency band around the main signal component to recover the rising edge pulse location information.

### Claim 2 (depends on 1)

The CMOS imaging sensor of claim 1, wherein the nonlinear resistor is a reset transistor, operated in a sub-threshold region in a selected pixel, which transistor is further used as a switch and turned on to maintain the sense node at a voltage reference in non-selected pixels.

### Claim 3 (depends on 2)

The CMOS imaging sensor of claim 2, wherein the control circuit is configured to operate said transistor as a nonlinear resistance in a selected pixel through controlling at least one of a gate signal or a voltage reference applied to the voltage supplying node of the pixel.

### Claim 4 (depends on 2)

The CMOS imaging sensor of claim 2, wherein the pixel structure of each pixel further comprises a transfer transistor connected in series between the sense node and the photodetector, wherein the transfer transistor is in the ON state all along the measurement phase, the transfer transistor then operating as a decoupling element between a photodetector node and the sense node and wherein the transfer transistor is also set in the ON mode in the unselected pixels.

### Claim 5 (depends on 1)

The CMOS imaging sensor of claim 1, in which the capacitance at the sense node of a pixel is no more than 5 femtofarads.

### Claim 6 (depends on 1)

The CMOS imaging sensor of claim 1, in which filter is implemented in the analog to digital convertor, after a sample and hold circuit and before a digitizing circuit.

### Claim 7 (depends on 1)

The CMOS imaging sensor of claim 1, in which filter is implemented in digital and operates on the digitized samples provided by the analog to digital convertor.

### Claim 8 (depends on 7)

The CMOS imaging sensor of claim 7, wherein digital implementation achieves a high pass filter through computing differences between two successive sampled signals.

### Claim 9 (depends on 7)

The CMOS imaging sensor of claim 7, in which the filter is a digital filter which is configured to extract pulse location and amplitude of the signal information in a high frequency range and at least background light noise in a low frequency range.

### Claim 10 (depends on 1)

The CMOS imaging sensor of claim 1, further comprising at least a power amplifier between a sense node of a selected pixel and the readout circuit, the power amplifier having a high impedance input and an impedance output matching an impedance of an output line to the readout circuit.

### Claim 11 (depends on 10)

The CMOS imaging sensor of claim 10, in which the power amplifier comprises at least a source follower output stage.

### Claim 12 (depends on 10)

The CMOS imaging sensor of claim 10, in which the output line is a transmission line.

### Claim 13 (depends on 1)

A direct time of flight system comprising a CMOS imaging sensor as claimed in claim 1, as a pulse light receiver, in which a light pulse source is operated to emit only one or a reduced number of light pulses, in a number lower than or equal to 5, per measurement phase.

### Claim 14 (depends on 3)

The CMOS imaging sensor of claim 3, wherein the pixel structure of each pixel further comprises a transfer transistor connected in series between the sense node and the photodetector, wherein the transfer transistor is in the ON state all along the measurement phase, the transfer transistor then operating as a decoupling element between a photodetector node and the sense node and wherein the transfer transistor is also set in the ON mode in the unselected pixels.

### Claim 15 (depends on 4)

The CMOS imaging sensor of claim 4, in which the capacitance at the sense node of a pixel is no more than 5 femtofarads.

### Claim 16 (depends on 5)

The CMOS imaging sensor of claim 5, in which the filter is implemented in the analog to digital convertor, after a sample and hold circuit and before a digitizing circuit.

### Claim 17 (depends on 5)

The CMOS imaging sensor of claim 5, in which the filter is implemented in digital and operates on the digitized samples provided by the analog to digital convertor.

### Claim 18 (depends on 9)

The CMOS imaging sensor of claim 9, further comprising a power amplifier between a sense node of a selected pixel and the readout circuit, the power amplifier having a high impedance input and an impedance output matching an impedance of an output line to the readout circuit.

### Claim 19

A method to operate a pixel in a CMOS imaging sensor for measuring a time occurrence of a rising edge of a light pulse having reached the pixel, the pixel having a structure comprising
a photodetector (PhD) exposed to light and operating as a current source,
a first reset transistor (TRST) connected between a supply voltage reference source and a capacitive sense node (SN) having a capacitance, wherein the sense node outputs a voltage signal, and wherein the first reset transistor and capacitance of the sense node are configured to operate as a low pass filter and to perform current to voltage conversion in a low frequency range and integration in a high frequency range,
wherein the method applies a measurement phase comprising:
continuously operating the first reset transistor as a nonlinear resistance;
converting, by the nonlinear resistance and capacitance, the signal received from the photodetector to produce a voltage signal at the sense node that has a main signal component comprising at least a rising edge pulse location information in the high frequency range, and a noise component mainly concentrated in the low frequency range spaced apart from said high frequency range;
continuously filtering out the voltage signal before or after analog to digital conversion through at least one of a band pass or a high pass filtering, resulting in increasing the signal to noise ratio in the frequency range of the filtering,
analog to digital conversion converting prior or after said continuous filtering, at a sampling frequency higher than a frequency value corresponding to the pulse light duration,
determining a location of a rising edge of the light pulse in the filtered digital signal through level triggering.