PHOTODIODE FRONT END WITH IMPROVED POWER SUPPLY REJECTION RATIO (PSRR)

• US 20110180693A1
• Filed: 01/25/2011
• Published: 07/28/2011
• Est. Priority Date: 01/27/2010
• Status: Abandoned Application

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Gibby, Aaron, Craddock, Carl Warren, Golden, Philip, Ritter, David W.
• Application Number:
  US13/013,199
• Publication Number:
  US 20110180693A1
• Time in Patent Office: Days
• US Class Current: 250/214.A
• 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

An area effective system and method for improving power supply rejection ratio (PSRR) in an optical sensor front end, is provided. Moreover, low pass filter (LPF) that enables the reference voltage in the front end of the optical sensor, to be referred to the same substrate as that employed by the sensor. In one example, the LPF includes a capacitor, implemented using a Deep-N-Well (DNW) depletion capacitor, which is utilized to connect the reference voltage to the same substrate. Additionally, the DNW allows an area efficient realization of the LPF. The system and method disclosed herein improves the PSRR by a factor of around 40 dB for 5 MHz modulation.

Claims

1. An apparatus with improved power supply rejection ratio (PSRR), comprising:

a filter having an input adapted to be coupled to a reference voltage, and an output;

a sensor having an output; and

an amplifier having first and second inputs where the first input is coupled to the filter output, and where the second input is coupled to the output of the sensor,

wherein the sensor and the filter have electrical nodes that are connected to the same region in a semiconductor substrate through a high resistance layer.

2. The apparatus of claim 1, wherein the filter includes a low pass filter (LPF).

3. The apparatus of claim 2, wherein the LPF includes a resistor and a capacitor (RC) pair.

4. The apparatus of claim 3, wherein the capacitor is implemented as a depletion capacitance by reverse biasing at least one of an N-well or a Deep-N-well (DNW) relative to the common substrate.

5. The apparatus of claim 3, wherein the capacitor is implemented as an n-channel metal oxide semiconductor (NMOS) transistor coupled to the common substrate via the high resistance layer.

6. The apparatus of claim 1, wherein the sensor includes a positive-intrinsic-negative (PIN) photodiode and wherein an anode of the PIN photodiode is connected to the common substrate.

7. The apparatus of claim 1, further comprising:

a voltage generator that generates the reference voltage signal.

8. The apparatus of claim 1, further comprising:

a signal processing circuit coupled to the output of the amplifier, wherein the signal processing circuit determines the proximity of an object within a sense area of the sensor.

9. The apparatus of claim 1, further comprising:

a signal processing circuit coupled to the output of the amplifier, wherein the signal processing circuit detects a distance at which motion occurred within a sense area of the sensor.

10. The apparatus of claim 1, further comprising:

a signal processing circuit coupled to the output of the amplifier, wherein the signal processing circuit determines an ambient light amount within a sense area of the sensor.

11. The apparatus of claim 1, further comprising:

a light emitting diode (LED) driver; and

a LED that emits a frequency modulated signal.

12. The apparatus of claim 11, wherein the sensor receives at least a portion of the frequency modulated signal reflected back from an object within a sense area of the sensor.

13. A method for reducing power supply rejection ratio, comprising:

generating a sensor signal from a sensor connected to and formed over a substrate;

generating a reference signal;

filtering said reference signal with a filter connected via a high resistance layer to and formed on the substrate; and

amplifying the difference between the sensor signal and the filtered reference signal.

14. The method of claim 13, wherein the filtering includes low pass filtering the reference signal.

15. The method of claim 13, further comprising:

utilizing the difference to identify at least one of proximity of an object, motion of an object or ambient light within a vision field of the sensor.

16. A system, comprising:

an optical sensor connected to and formed over a substrate;

an amplifier that sets a direct current (DC) bias point of the optical sensor by employing a reference voltage connected to the chip substrate; and

a low pass filter (LPF) that refers the reference voltage to the chip substrate through a layer with a resistance higher than that of the substrate.

17. The system of claim 16, wherein the optical sensor includes a positive-intrinsic-negative (PIN) diode.

18. The system of claim 16, wherein the LPF includes a resistor and a capacitor pair, and wherein the capacitor is connected to and formed over the chip substrate through the layer.

19. The system of claim 16, further comprising:

an N-well that refers the reference voltage to the substrate.

20. The system of claim 16, further comprising:

a Deep-N-well (DNW) that refers the reference voltage to the substrate.