DIRECT CURRENT (DC) CORRECTION CIRCUIT FOR A TIME OF FLIGHT (TOF) PHOTODIODE FRONT END

• US 20110181254A1
• Filed: 01/25/2011
• Published: 07/28/2011
• Est. Priority Date: 01/27/2010
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Brehmer, Kevin, Golden, Philip, Ritter, David W., Craddock, Carl Warren
• Granted Patent: US 8,530,819 B2
• Time in Patent Office: Days
• US Class Current: 323/234
• CPC Class Codes: G01J 1/46 using a capacitor
• CPC Class Codes: G01J 9/00 Measuring optical phase difference devices or arrangements for controlling the phase of light beams G02F1/01; Determining degree of coherence; Measuring optical wavelength spectrometry G01J3/00
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: H01L 31/101 Devices sensitive to infrared, visible or ultraviolet radiation

Abstract

A system and method that compensates for the effects of ambient light in a time of flight (TOF) sensor front end is provided. Moreover, a direct current (DC) correction loop is utilized at the front end, which removes a DC component from a current generated by the TOF sensor and accordingly prevents saturating the front end. The DC correction loop attenuates the DC component without adding significant thermal noise at a modulation frequency and provides a corrected signal to the front end circuitry. The corrected signal is processed and utilized to detect a position of an object within the optical field of the sensor.

Claims

1. An apparatus, comprising:

a sensor; and

a direct current (DC) correction loop coupled with the sensor;

wherein,

the DC correction loop for reducing a DC error generated in part by an ambient signal incident on the sensor; and

the DC correction loop generates less noise spectral density than the noise spectral density generated by one or more signal processing components included in the front end.

2. The apparatus of claim 1, wherein the DC correction loop is coupled in parallel with the sensor.

3. The apparatus of claim 1, wherein the sensor is a photodiode.

4. The apparatus of claim 1, wherein the DC correction loop emulates an inductor.

5. The apparatus of claim 1, wherein the DC correction loop includes a first amplifier that controls a bias of a second amplifier.

6. The apparatus of claim 5, wherein the DC correction loop includes a resistor and a capacitor pair that attenuates a noise transfer function of the first amplifier.

7. The apparatus of claim 5, wherein the second amplifier includes at least one of a p-channel metal-oxide-semiconductor (PMOS) device or a buffer.

8. The apparatus of claim 5, wherein the resistor is implemented as a metal-oxide-semiconductor (MOS) transistor.

9. The apparatus of claim 5, wherein an output of the second amplifier is provided as a feedback to an input of the first amplifier.

10. The apparatus of claim 1, further comprising:

a light emitting diode (LED) that emits light associated with a frequency modulated signal, wherein the light reflects off of an object and the sensor receives at least a part of the reflected light from the object.

11. A method that reduces direct current (DC) saturation in a sensor system, comprising:

generating a sensor signal including a DC component;

substantially subtracting the DC component from the sensor signal; and

adaptively reducing a thermal noise value introduced during the subtraction step whereby said thermal noise value is less than a disparate thermal noise value introduced by the subsequent signal processing.

12. The method of claim 11, further comprising:

frequency modulating an electrical signal; and

emitting a light associated with a frequency modulated signal.

13. The method of claim 12, further comprising:

receiving, at the sensor, at least a portion of the light reflected from one or more objects within the optical field.

14. The method of claim 13, wherein the adaptively reducing the thermal noise value includes adaptively controlling the thermal noise value introduced during the subtracting step at a modulation frequency.

15. The method of claim 13, further comprising:

processing the sensor signal to identify at least one of a distance of the one or more objects or a distance at which a motion occurred.

16. The method of claim 11, wherein the subtracting includes emulating an inductor that at least one of removes or reduces the DC component.

17. A system, comprising:

a sensor that generates an electric signal, which includes a low frequency component based in part on ambient light and a high frequency component based on light reflected from an object; and

a feedback loop, situated in parallel with the sensor, that passes the high frequency component to a front end device and at least one of eliminates or reduces the low frequency component without introducing thermal noise above a level of thermal noise introduced by a signal processing circuitry in a front end of the system.

18. The system of claim 17, wherein the feedback loop includes a resistor and a capacitor pair that attenuates a noise transfer function of a first amplifier, which controls a bias of a second amplifier.

19. The system of claim 18, wherein

a cathode of the sensor is connected to a non-inverting input of the first amplifier;

the resistor is connected between a reference voltage and an inverting input of the first amplifier;

the capacitor is connected between an output of the first amplifier and the inverting input of the first amplifier;

the output of the first amplifier is connected to a inverting input of the second amplifier; and

an output of the second amplifier is fed back to the cathode of the sensor.

20. The system of claim 18, wherein

the resistor is connected between a cathode of the sensor and an inverting input of the first amplifier;

the capacitor is connected between an output of the first amplifier and the inverting input of the first amplifier;

a non-inverting input of the first amplifier is connected to a reference voltage;

the output of the first amplifier is connected to a non-inverting input of the second amplifier; and

an output of the second amplifier is fed back to the cathode of the sensor.