Time of flight imaging with improved initiation signaling

Patent metadata

Field	Value
Publication number	US-2016353084-A1
Application number	US-201514721424-A
Country	US
Kind code	A1
Filing date	May 26, 2015
Priority date	May 26, 2015
Publication date	Dec 1, 2016
Grant date	—

Abstract

A time of flight sensor includes control circuitry and a time of flight pixel array. The control circuitry is coupled to synchronously send a sync signal. The time of flight pixel array includes a plurality of time of flight pixel cells. Each one of the time of flight pixel cells includes a photosensor and a delay circuit. The photosensor is configured to generate an image signal in response to receiving photons from a light pulse reflected from an object. The delay circuit is coupled to generate a delayed sync signal in response to the sync signal. The delay circuit includes a delay transistor. The time of flight pixel array includes a transistor gradient where a transistor gate length of the delay transistor varies so that each of the time of flight pixel cells receive their respective delayed sync signal at a same time.

First claim

What is claimed is:

1 . A time of flight sensing system, comprising:
a light source to emit light pulses to an object; control circuitry coupled to send a sync signal when one of the light pulses is emitted by the light source; and a time of flight pixel array having a plurality of time of flight pixel cells, wherein each one of the time of flight pixel cells comprises:
a photosensor configured to generate an image signal in response to receiving photons from the light pulse reflected from the object;
a delay circuit coupled to generate a delayed sync signal in response to the sync signal, wherein the delay circuit includes a delay transistor, and wherein the time of flight pixel array includes a transistor gradient where a transistor gate length of the delay transistor varies as the time of flight pixel cells get closer to a center of the time of flight pixel array so that each of the time of flight pixel cells receive their respective delayed sync signal at a same time; and
signal circuitry coupled to generate a distance signal in response to receiving the delayed sync signal and the image signal, wherein the distance signal is representative of a distance from the photosensor to the object.

2 . The time of flight sensing system of claim 1 , wherein the signal circuitry includes charging control logic coupled to generate a time of flight (TOF) signal in response to receiving the image signal and the delayed sync signal, the TOF signal representative of a time between emitting one of the light pulses and receiving the photons from the light pulse at the respective time of flight pixel cell.

3 . The time of flight sensing system of claim 2 , wherein the signal circuitry further includes a capacitor and a current source, wherein the current source supplies current to the capacitor to charge the capacitor in response to receiving the TOF signal from the charging control logic, a voltage on the capacitor representative of the distance from the photosensor to the object.

4 . The time of flight sensing system of claim 3 , wherein the signal circuitry further includes a reset circuit coupled to reset the voltage on the capacitor.

5 . The time of flight sensing system of claim 3 , wherein the signal circuitry further includes output circuitry including an amplifier coupled to the capacitor, wherein the amplifier is coupled to amplify the voltage on the capacitor onto a readout bitline.

6 . The time of flight sensing system of claim 3 , wherein the current sources in each of the time of flight pixel cells are coupled to a same reference current driver.

7 . The time of flight sensing system of claim 1 , wherein the transistor gate length decreases as the time of flight pixel cells get closer to the center of the time of flight pixel array.

8 . The time of flight sensing system of claim 7 , wherein the delay circuit includes an inverter that includes the delay transistor, and wherein the delay transistor is a P-channel Metal-oxide-semiconductor (PMOS) transistor.

9 . The time of flight sensing system of claim 1 further comprising readout circuitry coupled to readout the distance signal from each of the time of flight pixel cells.

10 . The time of flight sensing system of claim 1 , wherein the photosensor includes an avalanche photodiode.

11 . The time of flight sensing system of claim 1 , wherein the light source is an infrared light-emitting-diode (LED).

12 . A time of flight sensor, comprising:
control circuitry coupled to synchronously send a sync signal and an emission signal to a light source, wherein the emission signal activates the light source to emit a light pulse; and a time of flight pixel array having a plurality of time of flight pixel cells, wherein each one of the time of flight pixel cells comprises:
a photosensor configured to generate an image signal in response to receiving photons from the light pulse reflected from an object;
a delay circuit coupled to generate a delayed sync signal in response to the sync signal, wherein the delay circuit includes a delay transistor, and wherein the time of flight pixel array includes a transistor gradient where a transistor gate length of the delay transistor varies so that each of the time of flight pixel cells receive their respective delayed sync signal at a same time; and
signal circuitry coupled to generate a distance signal in response to receiving the delayed sync signal and the image signal, wherein the distance signal is representative of a distance from the photosensor to the object.

13 . The time of flight sensor of claim 12 , wherein the signal circuitry includes charging control logic coupled to generate a time of flight (TOF) signal in response to receiving the image signal and the delayed sync signal, the TOF signal representative of a time between emitting the light pulse and receiving the photons from the light pulse at the respective time of flight pixel cell.

14 . The time of flight sensor of claim 13 , wherein the signal circuitry further includes a capacitor and a current source, wherein the current source supplies current to the capacitor to charge the capacitor in response to receiving the TOF signal from the charging control logic, a voltage on the capacitor representative of the distance from the photosensor to the object.

15 . The time of flight sensor of claim 14 , wherein the signal circuitry further includes a reset circuit coupled to reset the voltage on the capacitor.

16 . The time of flight sensor of claim 14 , wherein the signal circuitry further includes output circuitry including an amplifier coupled to the capacitor, wherein the amplifier is coupled to amplify the voltage on the capacitor onto a readout bitline.

17 . The time of flight sensor of claim 14 , wherein the current sources in each of the time of flight pixel cells are coupled to a same reference current driver.

18 . The time of flight sensor of claim 12 , wherein the transistor gate length decreases as the time of flight pixel cells get closer to a center of the time of flight pixel array.

19 . The time of flight sensor of claim 18 , wherein the delay circuit includes an inverter that includes the delay transistor, and wherein the delay transistor is a P-channel Metal-oxide-semiconductor (PMOS) transistor.

20 . The time of flight sensor of claim 12 further comprising readout circuitry coupled to readout the distance signal from each of the time of flight pixel cells.

Assignees

• Omnivision Tech Inc

Inventors

• Sun Tianjia
• Wang Rui
• Dai Tiejun

Classifications

• H04N25/76

  Addressed sensors, e.g. MOS or CMOS sensors · CPC title

• H04N25/40 Primary

  Extracting pixel data from image sensors by controlling scanning circuits, e.g. by modifying the number of pixels sampled or to be sampled · CPC title

• H04N13/211

  using temporal multiplexing · CPC title

• G01S7/497

  Means for monitoring or calibrating · CPC title

• G01S17/894

  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 · CPC title