# US 12,192,644 B2 · Pulse-width modulation pixel sensor

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- Number: US 12,192,644 B2
- Document ID: US12192644B2
- Status: Granted
- Kind: B2
- Application number: 17/865,128
- Filed: 2022-07-14
- Published: 2023-02-09
- Granted: 2025-01-07
- Earliest claimed: 2021-07-29
- Assignees: Apple Inc.
- Applicants: Apple Inc.
- Inventors: Nikolai E. Bock; Andrew Kenneth John McMahon; Dario Clocchiatti; Emanuele Mandelli; Gennady A. Manokhin; Robert H. Mullis
- Web page: https://patentgrep.com/patent/US12192644B2

## CPC

- H04N 23/73: by influencing the exposure time
- G04F 10/005: {Time-to-digital converters [TDC] (analog-to-digital converters with intermediate conversion to time or phase H03M1/50, H03M1/60)}
- H04N 5/04: Synchronising (for television systems using pulse code modulation H04N7/56)
- H04N 23/71: Circuitry for evaluating the brightness variation
- H04N 25/53: Control of the integration time
- H04N 25/772: comprising A/D, V/T, V/F, I/T or I/F converters
- G11C 11/419: Read-write [R-W] circuits
- H10F 39/809: {of hybrid image sensors}
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION
- G04F: TIME-INTERVAL MEASURING (measuring pulse characteristics G01R, e.g. G01R29/02; in radar or like systems G01S)
- G11C: STATIC STORES (semiconductor memory devices H10B)
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION

## Abstract

A pulse-width modulation (PWM) image sensor is described herein. The PWM image sensor may have a stacked configuration. A top wafer of the PWM image sensor may have a charge-to-time converter and a logic wafer, stacked with the top wafer, may include a time-to-digital converter. The PWM image sensor may utilize variable transfer functions to avoid highlight compression and may utilize non-linear time quantization. A threshold voltage, as input to a charge-to-time converter, may additionally be controlled to affect light detection, dynamic range, and other features associated with the PWM image sensor.

## Claims

### Claim 1

A method of operation of a pulse-width modulation (PWM) image sensor, the method comprising:
during a detection period, receiving a number of photons at a PWM pixel of the PWM image sensor;
converting the number of photons into a photocurrent as the number of photons is received;
accumulating a number of electrons at a sense node during the detection period, the number of electrons accumulated in response to the sense node receiving the photocurrent;
during and in synchronization with the detection period, incrementing a count non-linearly, each value of the count synchronized with a non-linear time reference; and
when the accumulated number of electrons reaches a threshold number of electrons, latching a value of the count in a memory of a time-to-digital converter (TDC) circuit.

### Claim 2 (depends on 1)

The method of claim 1, wherein:
the value of the count is latched in the memory at a triggering time, the triggering time having a non-linear relationship with the photocurrent; and
as the triggering time increases, the count increments at a decreased rate.

### Claim 3 (depends on 1)

The method of claim 1, wherein the time reference, t, is defined by
t
=
2
b
*
t
min
2
b
-
n
,
where p is a bit depth or the TDC circuit, n is a counter step number, and tmin is a counter delay.

### Claim 4 (depends on 3)

The method of claim 3, wherein the counter delay is further defined by
t
min
=
q
*
N
T
⁢
H
I
max
,
where q is an elementary charge, NTH is the threshold number of electrons, and Imax is a maximum producible photocurrent.

### Claim 5 (depends on 1)

The method of claim 1, further comprising transmitting image information, corresponding to the latched value of the count in the memory of the TDC circuit, via a bi-directional bus.

### Claim 6 (depends on 1)

The method of claim 1, further comprising terminating a duration of the detection period in response to the photocurrent.

### Claim 7 (depends on 6)

The method of claim 6, wherein a higher photocurrent results in a shorter detection period and a lower photocurrent results in a longer detection period.