US20110180693A1

US20110180693A1 - Photodiode front end with improved power supply rejection ratio (psrr)

Info

Publication number: US20110180693A1
Application number: US13/013,199
Authority: US
Inventors: David W. Ritter; Philip Golden; Aaron Gibby; Carl Warren Craddock
Original assignee: Intersil Americas LLC
Current assignee: Intersil Americas LLC
Priority date: 2010-01-27
Filing date: 2011-01-25
Publication date: 2011-07-28
Also published as: US20110180709A1; TW201203008A; TWI445993B; WO2011094364A1; WO2011094365A1; CN102822691A; TW201202731A; US10031078B2; US20110181861A1; US20110182519A1; US8530819B2; US8274037B2; TW201202730A; CN106052862B; TWI439716B; CN106052862A; US8760631B2; WO2011094362A1; US20110181254A1; TWI531809B

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.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Ser. No. 61/298,895, filed on Jan. 27, 2010, and entitled “ARCHITECTURE FOR A REFLECTION BASED LONG RANGE PROXIMITY AND MOTION DETECTOR HAVING AN INTEGRATED AMBIENT LIGHT SENSOR.” Further, this application is related to co-pending U.S. patent application Ser. No. 12/979,726, filed on Dec. 28, 2010 (Attorney docket number SE-2773/INTEP105USA), entitled “DISTANCE SENSING BY IQ DOMAIN DIFFERENTIATION OF TIME OF FLIGHT (TOF) MEASUREMENTS,” co-pending U.S. patent application Ser. No. ______, filed on ______ (Attorney docket number SE-2784-AN/INTEP105USB), entitled “DIRECT CURRENT (DC) CORRECTION CIRCUIT FOR A TIME OF FLIGHT (TOF) PHOTODIODE FRONT END”, co-pending U.S. patent application Ser. No. ______, filed on ______ (Attorney docket number SE-2876-AN/INTEP105USD), entitled “AUTOMATIC ZERO CALIBRATION TECHNIQUE FOR TIME OF FLIGHT (TOF) TRANSCEIVERS,” co-pending U.S. patent application Ser. No. ______, filed on ______ (Attorney docket number SE-2877-AN/INTEP105USE), entitled “SERIAL-CHAINING PROXIMITY SENSORS FOR GESTURE RECOGNITION”, and co-pending U.S. patent application Ser. No. ______, filed on ______ (Attorney docket number SE-2878-AN/INTEP105USF), entitled “GESTURE RECOGNITION WITH PRINCIPAL COMPONENT ANALYSIS.” The entireties of each of the foregoing applications are incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary system which reduces power supply noise during distance, motion and/or ambient light sensing.
FIG. 2 illustrates an exemplary cross section of a photodiode and a low pass filter (LPF) employed to improve power supply rejection ratio (PSRR).
FIG. 3 illustrates an exemplary improved photodiode front end PSRR in optical sensing applications.
FIG. 4 illustrates an exemplary methodology that can improve PSRR for a front end of an optical detector.
FIG. 5 illustrates an exemplary functional block diagram for the architecture of the subject innovation.

DETAILED DESCRIPTION

A category of monolithic devices is emerging that allows electronic products to sense their environment. These include diverse devices, such as, accelerometers, monolithic gyroscopes, light sensors and imagers. In particular, light sensors are one of the simplest and cheapest, allowing their inclusion in multitudes of consumer products, for example, nightlights, cameras, cell phones, laptops etc. Typically, light sensors can be employed in a wide variety of applications related to proximity sensing, such as, but not limited to, detecting the presence and/or distance of a user to the product for the purpose of controlling power, displays, or other interface options.
Infrared (IR) detectors utilize IR light to detect objects within the sense area of the IR sensor. Moreover, IR light is transmitted by an IR Light emitting diode (LED) emitter, which reflects off of objects in the surrounding area and the reflections are sensed by a detector. Moreover, the detector can be a diode, e.g., a PIN diode, and/or any other type of apparatus that converts IR light into an electric signal. The sensed signal is analyzed to determine whether an object is present in the sense area and/or detect motion within the sense area. In addition, the detector can be utilized to identify the ambient light, which can be utilized to control system parameters, such as, but not limited to, screen brightness, power saving modules, etc. Moreover, the light sensed by a detector is converted to a current (or voltage) signal, which is then processed by the detector front end circuitry. Typically, conventional systems suffer from power supply rejection ratio (PSRR) issues due to noise introduced by the reference voltage utilized in the front end circuitry. PSRR issues at the front end can cause significant errors in calculation and provide inaccurate results for proximity, motion and ambient light detection. In one example, the “front end” as disclosed herein, can include amplifier(s), filter(s), demodulator, most any analog and/or digital signal processing circuits, and/or most any circuits that conform, the signal generated by the sensor to a specification, a back end can use. For example, the front end can include one or more amplifiers, one or more Analog-to-Digital converters (ADC), and/or a signal processor.
The systems and methods disclosed herein provide a novel approach for improving the PSRR in the front end of an optical detector. Specifically, the approach disclosed herein refers the reference voltage to the same substrate as that employed by the optical detector through a high resistance layer (e.g., epitaxial layer), and additionally allows a very efficient area realization of a low pass filter (LPF). In one aspect, the optical detector can include a photodiode utilized within an active long-range IR distance sensor. For example, the range of the disclosed IR distance sensor can be 1-2 meters. Typically, the light emitted by the IR LED is modulated at a high frequency, for example 1 MHz-50 MHz. Moreover, most any modulation scheme can be employed, such as, but not limited to, frequency modulation, chirp modulation, Quadrature amplitude modulation, etc. The received IR response is then demodulated by and processed to detect motion or distance of an object. It can be appreciated that although the subject specification is described with respect to IR light, the systems and methods disclosed herein can utilize most any wavelength. As an example, the subject system and/or methodology can be employed for acoustical proximity detection and/or ultrasonic range finding applications. Further, although the subject specification describes a light sensor, it can be appreciated that most any sensor formed over and/or coupled to a chip substrate can be utilized.
The subject matter is described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the subject innovation. It may be evident, however, that the subject matter may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the subject innovation. Of course, those skilled in the art will recognize that many modifications may be made to this configuration without departing from the scope or spirit of the claimed subject matter.
Moreover, the word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word “exemplary” is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. In addition, the word “coupled” is used herein to mean direct or indirect electrical or mechanical coupling. Further, the terms “sense area,” “vision field,” “optical field,” and similar terminology are utilized interchangeably in the subject application, unless context warrants particular distinction(s) among the terms.
Referring initially to FIG. 1, there illustrated an example system that includes an Integrated Circuit (‘IC’) 102, which employs an optical detector to facilitate distance, motion and/or ambient light sensing, according to an aspect of the subject specification. Moreover, the IC 102 provides an improved PSRR at the front end of the detector and reduces errors during sensing. The IC 102 can include a Vref generator 104, a LPF 106, and/or a sensor front end 108. It can be appreciated that although the Vref generator 104, LPF 106, and sensor front end 108, are depicted to reside within a single IC 102, the subject innovation is not so limited and that the Vref generator 104 or other constituents can reside outside IC 102.
According to an embodiment, the Vref generator 104 can include most any voltage generator that generates a constant reference voltage of Vref_block volts. Typically, the Vref generator 104 is susceptible to noise variations resulting in output fluctuations in Vref_block. To eliminate the output fluctuations and improve PSRR, LPF 106 is employed. In one aspect, the LPF 106 is implemented in the same silicon as an optical sensor (e.g., photodiode) by employing a buried contact to a common substrate. In particular, the capacitor within the LPF 106 can be connected in a manner such that the voltage Vref is referenced to a substrate that is common to an optical sensor, for example, a photodiode. Moreover, the LPF 106 has a direct electrical connection with the common substrate through a high resistance layer, for example, an epitaxial layer. Typically, the resistance of the epitaxial layer can be 2-3 orders of magnitude higher in resistivity than the common substrate.
Further, the LPF 106 can include a capacitor implemented as a depletion capacitance by reverse biasing a Deep-N-well (DNW) connected to the common substrate, which enables the reference voltage to be referred to the same substrate as the photodiode, which in turn allows a very efficient area realization of the LPF 106. In an example, the DNW can be utilized for the cathode of the diode. Conventional photodiode front ends can suffer from PSRR issues due to the fact that the diode is referred to the actual chip substrate, while the reference voltage is referred to a substrate contact on the topside of the die. In contrast, the subject system of FIG. 1, provides reference generation by combining an intrinsic layer photodiode (e.g., available as a module in processes 0.6μm and above), with a Deep-N-well (DNW) (e.g., available in much finer line Complementary metal-oxide-semiconductor (CMOS) processes). Moreover, the LPF 106, as disclosed herein, provides a significant (e.g., 40 dB) improvement in PSRR in a very area efficient manner. Additionally or alternately, the capacitor of the LPF 106 can be built using an n-channel metal-oxide-semiconductor (NMOS) transistor. The NMOS transistor can provide a high capacitance/unit area as compared to the capacitor built with a depletion region, and can be utilized if the reference voltage is large enough to turn on the NMOS transistor. Typically, a high voltage NMOS transistor can be employed with deep junctions into the epi layer, which would have better performance to the substrate.
The voltage, Vref, provided by the LPF 106, can be employed by the sensor front end 108. For example, the sensor front end 108 can include amplifier(s), filter(s), demodulator, most any analog and/or digital signal processing circuits, and/or most any circuits that conform the signal generated by the sensor to a specification that a back end can use. In accordance with an embodiment, the sensor front end 108 can provide an output signal utilized by one or more applications, such as, but not limited to detecting ambient light levels, detecting the proximity of an object or person (based on time of flight (TOF) measurements), and/or detecting motion (based on a change in phase in the light reflected from a moving object). Typically, the applications including proximity detection and/or motion detection can be completely or substantially independent of the ambient light detection, even though the applications can utilize the same optical detector.
Referring now to FIG. 2, there illustrated is an example cross section 200 of a photodiode and LPF employed to improve PSRR, according to an aspect of the disclosure. Typically, an optical detector can be a photodiode, e.g., a positive-intrinsic-negative (PIN) diode 202, and/or any other type of apparatus that converts light into an electric signal. The PIN diode 202 includes a neutrally doped depletion region sandwiched between p-doped and n-doped semiconducting regions. Typically, the depletion region is lightly doped and the p-doped and n-doped semiconducting regions are heavily doped. The PIN diode 202 exhibits an increase in its electrical conductivity as a function of the intensity, wavelength, and/or modulation rate of the incident radiation. In one example, the electrical signal generated by the PIN diode 202 is provided to an inverting input of an amplifier 204, for example, a differential operational amplifier (Op-Amp).
In one aspect, the non-inverting input of the amplifier 204 can be connected to a reference voltage (Vref). Conventionally, the detector front end suffers from poor PSRR; however, LPF 106 significantly improves the PSRR by referring the reference voltage to the same substrate 206 as that of the PIN diode 202 through an epitaxial (epi)/high resistance layer 208. In one example, the common substrate is connected to a reference voltage (e.g., ground). Additionally, LPF 106 provides a very efficient area realization. Typically, the substrate 206 can be most any base layer of an integrated circuit, onto which another layer(s), for example, the epi layer 208, is deposited to form the circuit. As an example, the substrate can be made of most any material, such as, but not limited to Silicon, Sapphire, etc. and can be part of the wafer from which the die is cut. The epi layer 208 can be most any high resistance layer including, but not limited to, a single crystal layer formed on top of the substrate 206 that provides a high resistance. Typically, the epi layer 208 and the substrate 206 have different doping levels and/or the epi layer 208 can be made of a completely different type of material than the substrate 206.
According to an embodiment, the amplifier 204 is utilized to set the direct current (DC) bias point of the PIN diode 202 at the desired value to create the necessary field in the PIN diode 202. For a traditional PIN diode this can cause a PSRR problem, since the PIN diode uses the chip substrate 206 as its anode, while this node is typically not accessible to a designer due to the thick intrinsic epi region 208. However, the subject innovation utilizes LPF 106, for example, simple RC filter wherein the capacitor is implemented by employing an N-well, and/or Deep-N-Well (DNW) depletion capacitor and/or a NMOS transistor. In one example, the capacitor is implemented as a depletion capacitance by reverse biasing an N-well relative to the common substrate or by reverse biasing a DNW connected to the common substrate. Typically, the DNW provides area efficient realization of the RC filter than a simple N-well implant. In another example, the capacitor can be implemented by employing a NMOS transistor to provide high capacitance per unit area. As shown, the LPF 106 allows the reference voltage to be referred to the actual chip substrate 206. Moreover, by employing the LPF 106, connected to the substrate 206, the PSRR is substantially improved, for example, by a factor of at least 40 dB for 5 MHz modulation.
It can be appreciated that the resistor R 210 can have most any suitable resistance value and capacitor C 212 can have suitable capacitance value (or ratios) depending on the application. Further, the amplifier 204 can include an operational-amplifier (Op-Amp) that can be set to provide a specific/maximum gain. In addition, although amplifier 204 is illustrated and described herein with a non-inverting and inverting input, it can be appreciated that most any amplifier and/or any front end element, which holds the capacitor (C) 212 at the reference voltage, can be utilized. Moreover, the voltage reference provided to the front end (e.g., amplifier 204, or any front end circuit element) enables the front end to pin the sensor 202 at that voltage.
FIG. 3 illustrates an example system 300 with improved photodiode front end PSRR during optical sensing applications, in accordance with an aspect of the subject disclosure. In general, system 300 can be employed in most any light sensing application. For example, a laptop or personal computer can power-up (e.g., from hibernation, stand-by, etc.) on detecting that a user has entered a room. In another example, a cell phone or personal digital assistant (PDA) can switch off a display (to conserve battery life) when detected that the phone/PDA is held at the user's ear. In yet another example, a computer monitor or television, can automatically adjust screen brightness or contrast settings based on ambient light detected by the sensor. Typically, system 300 utilizes a detector that is integrated into IC form, where the IC substrate has a high resistance epitaxial layer.
In one aspect, system 300 for optical sensing can employ an LED 302, for example, an infrared (IR) LED and a sensor 202, for example, IR sensor. Typically, for long range proximity detection, the system 300 can employ a high frequency (e.g., 5 MHz) modulated LED 302 and a tuned PIN detector 202 to optimize the detection range. Moreover, a LED driver 306 can be employed to provide an input signal to the LED 302 (e.g., frequency modulated signal). Typically, a local oscillator (not shown) synchronous with the LED driver can be utilized for synchronous detection (e.g., by the sensor front end 108). As an example, the LED 302 can have a typical peak wavelength that matches the proximity sensor spectrum, a narrow viewing angle with higher radiant intensity that can facilitate concentrating the energy that is ideal for proximity sensing. It can be appreciated that most any LED (or array) can be employed based on the factors, such as, but not limited to, view-angle, mechanic height, footprint, radiant intensity, current consumption, etc. Further, the LED 302 can emit the signal 308 (e.g., modulated IR signal) to the sensing object 310, and the sensor 202 can receive a portion 312 of the transmitted signal, which is reflected back from the surface of sensing object 310. The object 310 can be most any entity of interest, such as, but not limited to, a human entity, an automated component, a device, an item, an animal, etc.
In addition to the reflections 312 from the object 310, the sensor 202 can receive various other signals 314, such as, but not limited to, electrical crosstalk, optical crosstalk and/or environmental backscatter. Of these interferences, electrical and optical crosstalk can be approximated to be relatively constant through the life time of the device, and can be calibrated at the manufacturing or development stage of the application. Environmental backscatter 314 can be received from various sources in the optical field of the sensor 202, and can include ambient light from most any source other than the object 310. For example, ambient light comprises low frequency light including sunlight, artificially generated light (e.g., intended to light a room or an area) and/or light/shadows from objects that may not be of interest, such as, but not limited to a desk surface, a couch, a television display, a soda can, etc., higher frequency variations from manmade sources such as 100 Hz or 120 Hz light with various higher harmonics from lights driven directly from the power lines, and/or higher frequencies from florescent lighting driven with small transformer circuits in the 100 Khz frequency range and those harmonics.
The light sensor 202 produces a current (or voltage) indicative of both detected ambient light and light 312, reflected back from the object 310. This current signal is provided to the inverting (−) input of an amplifier within the sensor front end 108, which causes a large rising voltage to occur at the output of the amplifier in response to an increasing photo current. As described above, the non-inverting (+) input of the amplifier is connected to a reference voltage, generated by voltage generator 104, via a LPF 106. In one aspect, the LPF can comprise a RC pair (210,212), wherein the capacitor is connected to a substrate, to which the anode of the sensor 202 is connected, through a high resistance epi layer. Moreover, the capacitor is implemented as a depletion capacitance by reverse biasing an N-well relative to the common substrate, or a DNW connected to the common substrate and/or a High Voltage NMOS transistor with deep junctions into the epi layer. By referencing the LPF to the common substrate through the epi layer, the interference in the reference voltage can be significantly reduced. Typically, the sensor front end 108 can further include additional amplifier(s), and/or filter(s) and circuit(s) that provide the high frequency light source signal (signal reflected back from object 310) to a motion detector 316 and/or a proximity detector 318, and circuit(s) that provide the signal indicative of ambient light to an ambient light sensor 320.
In one example, the motion detector 316 can process the signal to identify a distance at which motion occurred. It can be appreciated that most any circuit for motion detection can be utilized. Further, the proximity detector 318 can include a circuit that utilizes Time-of-Flight (TOF) measurements, which rely on the finite speed of light to identify distance of the object 310 to detect the proximity of an object in the sense area. Furthermore, the ambient light sensor 320 can include a circuit that extracts the current indicative of the ambient light incident on the sensor 202. The ambient light current detected by the ambient light sensor 320 can be provided to various control system, such as, but not limited to a display backlight controller, or a camera setting controller, etc.
It can be appreciated that the mechanical design of system 300 can include different component selections, component placement, dimensions, glass cover characteristics, LED selections, isolation techniques between sensor 202 and LED 302, etc., to achieve an optimal proximity sensing. Moreover, LED 302 can be most any light source, such as, but not limited to an LED, an organic LED (OLED), a bulk-emitting LED, a surface-emitting LED, a vertical-cavity surface-emitting laser (VCSEL), a super luminescent light emitting diode (SLED), a laser diode, a pixel diode, or the like. It can be appreciated that the light source can produce IR light, or light of most any other wavelength. Additionally, it can be appreciated that the sensor 202 can include most any light detecting elements, such as, but not limited to, a photo resistor, photovoltaic cell, photodiode, phototransistor, charge-coupled device (CCD), or the like, that can be used to produce a current or voltage indicative of the magnitude of detected light, wherein the light detecting elements are referenced to the same substrate as the LPF.
Further, it can be appreciated that the LED driver 306, sensor front end 108, voltage generator 104, LPF 106, motion detector 316, proximity detector 318, and ambient light sensor 320 can include most any electrical circuit(s) that can include components and circuitry elements of any suitable value in order to implement the embodiments of the subject innovation. Furthermore, the LED driver 306, voltage generator 104, motion detector 316, proximity detector 318, and ambient light sensor 320, can be implemented on one or more integrated circuit (IC) chips or apparatus. Typically, various IR bands can be employed in imaging systems (e.g., Near IR, Mid-Wave IR and Long-Wave IR). Each band can have unique LEDs and Sensors. Oftentimes, some visible detector systems can work in the Near IR band and can include the detector integrated into the system IC. In addition, it can be appreciated that system 300 is not limited to utilizing IR light, and LEDs/sensors/detectors can utilize signals of most any wavelength.
FIG. 4 illustrates a methodology and/or flow diagram in accordance with the disclosed subject matter. For simplicity of explanation, the methodologies are depicted and described as a series of acts. It is to be understood and appreciated that the subject innovation is not limited by the acts illustrated and/or by the order of acts, for example acts can occur in various orders and/or concurrently, and with other acts not presented and described herein. Furthermore, not all illustrated acts may be required to implement the methodologies in accordance with the disclosed subject matter. In addition, those skilled in the art will understand and appreciate that the methodologies could alternatively be represented as a series of interrelated states via a state diagram or events. Additionally, it should be further appreciated that the methodologies disclosed hereinafter and throughout this specification are capable of being stored on an article of manufacture to facilitate transporting and transferring such methodologies to computers. The term article of manufacture, as used herein, is intended to encompass a computer program accessible from any computer-readable device or computer-readable storage/communications media.
FIG. 4 illustrates an example methodology 400 that can improve PSRR for a front end of an optical detector. Typically, methodology 400 can be employed in optical detectors utilized for various applications, such as, but not limited to consumer electronic devices (e.g., cell phones, laptops, media players, gaming systems, night-vision systems, etc.), mechanical systems (e.g., door/window mechanism), industrial automation systems, robotics, etc.
At 402, a reference voltage signal, for example, generated by an on-chip or off-chip voltage generator, can be received. At 404, the reference voltage signal can be filtered by employing a LPF that is referred, through an epi layer, to a substrate, which is common to a sensor (e.g., photodiode) utilized by the optical detector. For example, the LPF can include an RC filter, wherein the capacitor can be implemented by reverse biasing an N-well relative to the common substrate or a DNW that connects to the common substrate, or a high voltage NMOS transistor connected to the common substrate with a deep junction into the high resistance layer. Typically, the DNW provides an improved area efficient realization of the RC filter than a simple N-well implant. At 406, the filtered reference voltage signal is provided to a non-inverting end of a front end amplifier. In one example, the front end amplifier is employed to set the DC bias point of the photodiode at the desired value to create the necessary field in the photodiode.
Further, at 408 a signal indicative of incident light can be generated by employing a sensor, such as, but not limited to, a photodiode, connected to the common substrate. For example, the photodiode can utilize the common substrate as an anode. Typically, the incident light can include light reflected back from objects (moving and/or stationary) within the optical field and/or ambient light (e.g., sunlight, florescent lights, lamps, bulbs, etc.). Moreover, optical filters of most any wavelength can also be utilized with the photodiode to generate a current indicative of light specific to the particular wavelength. In one aspect, at 410, the signal generated by the sensor can be provided to the inverting input of the front end amplifier. Typically, the output of the amplifier can be filtered, demodulated and/or further amplified, and provided to circuits to detect motion, proximity and/or ambient light.
In order to provide additional context for various aspects of the subject specification, FIG. 5 illustrates an exemplary functional block diagram for the architecture 500 of the subject innovation. In one aspect, the systems (e.g., FIGS. 1-3) disclosed herein can be employed in a reflection based proximity and motion detector with/without an integrated ambient light sensor (ALS). The architecture 500 includes a LED and associated driver circuitry (not shown for simplicity), a photodiode sensor 202, an analog front end and signal processing 504, data conversion circuitry 506, digital control and signal processing 508 (e.g., a complex programmable logic device (CPLD), interface circuitry and results display (not shown for simplicity). The architecture 500 adaptively optimizes sensitivity and power for a given environment. Moreover, the architecture 500 derives significant performance improvements by reducing error at one of the most sensitive points in the circuit, for example, at the non-inverting terminal of a front end amplifier.
According to an aspect of the subject innovation, the architecture 500 includes a Front end (FE), which includes an amplifier 204, for example, a Trans-Inductance Amplifier (TIA). In one example, there can be a switch across the amplifier resistor in FIG. 5 (not shown). Typically, the front end section 502 provides an amplifier is used to set the DC bias point of the photodiode 202 at the desired value to create the necessary field in the diode 202. Moreover, a filter 106, for example, an RC filter where the capacitor (C) 212 is implemented using a DNW depletion capacitor, allows the reference voltage to be referred to the actual chip substrate through a high resistance epi-layer. This improves PSRR by a factor of about 40 dB for 5 MHz modulation.
Typically, the output of the Front end 502 can subjected to multiple stages of voltage gain to maximize the SNR of the output signal. In one example, the voltage gain is adaptively set based on the magnitude of the signal received from the Front end 502, which is potentially made up of both measureable interferers such as errors due to fluctuation in reference voltage, and also the desired signal to be measured. The interferers are dynamically calibrated out of the measurement to improve the sensitivity (e.g. by LPF 106). The architecture 500 also includes a Demodulator (not shown for simplicity) with low pass filters (LPFs), Analog to Digital Converters (ADCs) 506, a Universal Serial Bus (USB) processor for a Control Interface, and/or a Computer Programmable Logic Device (CPLD) that include several modules. Moreover, the digital signal processor (DSP) 806 can process the digital signal to identify proximity of an object, motion of an object and/or presence of an object within a sense field of the sensor 302.
The architecture 500 of the subject innovation can be used in many applications including computers, automotive, industrial, television displays and others. For example, the architecture 500 can be used to detect that a user has entered the room and automatically cause a laptop computer in hibernation mode to wake up and enter into the active mode so that the user can use it. In another example, the architecture 500 of the subject innovation can be used to automatically and adaptively adjust the intensity of a liquid crystal display (LCD) based on the ambient lighting conditions. According to an aspect of the subject innovation, the architecture 500 can perform motion and proximity sensing at a range of up to 1-2 meters. According to another aspect of the subject innovation, the architecture 500 of the subject innovation can perform its operations by using less than twenty milli-watts (mW) of power.
In one embodiment of the subject innovation, the entire architecture 500 can be implemented in a single integrated circuit chip (IC) along with the LED driver circuitry and the LED. In another embodiment of the subject innovation, all components of the architecture 500 can be implemented in the IC except for the Voltage generator 104, ADC 506, and DSP 508, which can be implemented outside the IC.
What has been described above includes examples of the subject innovation. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the claimed subject matter, but one of ordinary skill in the art may recognize that many further combinations and permutations of the subject innovation are possible. Accordingly, the claimed subject matter is intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.
In particular and in regard to the various functions performed by the above described components, devices, circuits, systems and the like, the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., a functional equivalent), even though not structurally equivalent to the disclosed structure, which performs the function in the herein illustrated exemplary aspects of the claimed subject matter. In this regard, it will also be recognized that the innovation includes a system as well as a computer-readable medium having computer-executable instructions for performing the acts and/or events of the various methods of the claimed subject matter.
The aforementioned systems/circuits/modules have been described with respect to interaction between several components. It can be appreciated that such systems/circuits/modules and components can include those components or specified sub-components, some of the specified components or sub-components, and/or additional components, and according to various permutations and combinations of the foregoing. Sub-components can also be implemented as components communicatively coupled to other components rather than included within parent components (hierarchical). Additionally, it should be noted that one or more components may be combined into a single component providing aggregate functionality or divided into several separate sub-components, and any one or more middle layers, such as a management layer, may be provided to communicatively couple to such sub-components in order to provide integrated functionality. Any components described herein may also interact with one or more other components not specifically described herein but generally known by those of skill in the art.
In addition, while a particular feature of the subject innovation may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “includes,” “including,” “has,” “contains,” variants thereof, and other similar words are used in either the detailed description or the claims, these terms are intended to be inclusive in a manner similar to the term “comprising” as an open transition word without precluding any additional or other elements.

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.