US20150260571A1 - Time-of-flight (tof) receiver with high dynamic range - Google Patents
Time-of-flight (tof) receiver with high dynamic range Download PDFInfo
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- US20150260571A1 US20150260571A1 US14/644,308 US201514644308A US2015260571A1 US 20150260571 A1 US20150260571 A1 US 20150260571A1 US 201514644308 A US201514644308 A US 201514644308A US 2015260571 A1 US2015260571 A1 US 2015260571A1
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- 238000007493 shaping process Methods 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
- G01J1/44—Electric circuits
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M3/00—Conversion of analogue values to or from differential modulation
- H03M3/30—Delta-sigma modulation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M3/00—Conversion of analogue values to or from differential modulation
- H03M3/30—Delta-sigma modulation
- H03M3/458—Analogue/digital converters using delta-sigma modulation as an intermediate step
- H03M3/494—Sampling or signal conditioning arrangements specially adapted for delta-sigma type analogue/digital conversion systems
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M3/00—Conversion of analogue values to or from differential modulation
- H03M3/30—Delta-sigma modulation
- H03M3/39—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators
- H03M3/402—Arrangements specific to bandpass modulators
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M3/00—Conversion of analogue values to or from differential modulation
- H03M3/30—Delta-sigma modulation
- H03M3/39—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators
- H03M3/412—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators characterised by the number of quantisers and their type and resolution
- H03M3/422—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators characterised by the number of quantisers and their type and resolution having one quantiser only
- H03M3/43—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators characterised by the number of quantisers and their type and resolution having one quantiser only the quantiser being a single bit one
Definitions
- the present disclosure is generally related to time-of-flight (TOF) systems, and more particularly to achieving high dynamic range in a receiver associated with a TOF system.
- TOF time-of-flight
- a TOF system includes a light source that emits light pulses. The light pulses are emitted towards a target, which reflects the light pulses.
- the target is any object of interest which may include, but not limited to, a human, an automated component, an animal, an electronic device etc.
- a TOF sensor in the TOF system receives the reflected light pulses. The TOF sensor receives the reflected light pulses after a time of flight, which is proportional to a distance of the target from the TOF system.
- the TOF sensor includes one or more TOF sensor pixels.
- Each TOF sensor pixel includes a receiver.
- the receiver processes the reflected light pulses to estimate the distance of the target from the TOF system.
- the receiver also receives other signals such as, but not limited to, electrical interferences, crosstalk signals and ambient light.
- the ambient light is due to one or more of the following, but not limited to, florescent lamps, sunlight, bulbs etc.
- the ambient light causes a direct current (DC) signal being generated in the receiver.
- a high DC signal saturates the receiver. This causes an error in estimating the distance of the target from the TOF system.
- a signal strength of the reflected light pulse is 30 dB whereas an interference generated is of the order of 100 dB.
- a receiver with high dynamic range is required.
- a receiver includes a photodiode that generates a current signal.
- a coupling capacitor is coupled to the photodiode, and generates a modulation signal in response to the current signal received from the photodiode.
- a sigma delta analog to digital converter (ADC) is coupled to the coupling capacitor, and generates a digital data in response to the modulation signal.
- a digital mixer is coupled to the sigma delta ADC, and generates an in-phase component and a quadrature component corresponding to the digital data.
- a processor is coupled to the digital mixer, and processes the in-phase component and the quadrature component corresponding to the digital data.
- FIG. 1 illustrates a receiver
- FIG. 2 illustrates a receiver, according to an embodiment
- FIG. 3 illustrates an ambient cancellation circuit, according to an embodiment
- FIG. 4 illustrates a loop filter, according to an embodiment
- FIG. 5 illustrates a continuous time resonator, according to an embodiment
- FIG. 6 illustrates a summer, according to an embodiment
- FIG. 7 illustrates a time-of-flight (TOF) system, according to an embodiment.
- FIG. 1 illustrates a receiver 100 .
- the receiver 100 includes a photodiode 102 , a trans-impedance amplifier (TIA) 110 , a mixer I 114 , a mixer Q 116 , a first filter and gain block 118 , a second filter and gain block 120 , a first analog to digital converter (ADC) 124 , a second analog to digital converter (ADC) 126 and a processor 130 .
- TIA trans-impedance amplifier
- ADC analog to digital converter
- ADC second analog to digital converter
- the photodiode 102 includes a sensor 104 and an associated capacitance C D 106 .
- the TIA 110 is coupled to the photodiode 102 .
- the mixer I 114 and the mixer Q 116 are coupled to the TIA 110 .
- the first filter and gain block 118 is coupled to the mixer I 114 .
- the second filter and gain block 120 is coupled to the mixer Q 116 .
- the first ADC 124 is coupled to the first filter and gain block 118 .
- the second ADC 126 is coupled to the second filter and gain block 120 .
- the processor 130 is coupled to the first ADC 124 and the second ADC 126 .
- the receiver in one example is used in a time-of-flight (TOF) system.
- the TOF system includes a light source that emits light pulses. The light pulses are emitted towards a target, which reflects the light pulses.
- the receiver 100 in the TOF system receives the reflected light pulses.
- the receiver 100 receives the reflected light pulses after a time of flight, which is proportional to a distance of the target from the TOF system.
- the sensor 104 in the photodiode 102 receives the reflected light pulses.
- the associated capacitance C D 106 stores a charge corresponding to the reflected light pulses.
- the charge represents a modulated signal received by the photodiode 102 .
- the charge stored in the associated capacitance C D 106 is received by the TIA 110 .
- the TIA 110 demodulates the modulated signal to generate an in-phase voltage and a quadrature voltage.
- the in-phase voltage is receiver by the mixer I 114 , and the quadrature voltage is received by the mixer Q 116 .
- the mixer I 114 multiplies the in-phase voltage and a voltage corresponding to the light pulses generated by the TOF system, to generate an in-phase voltage component.
- the mixer Q 116 multiplies the quadrature voltage and the voltage corresponding to the light pulses generated by the TOF system, to generate a quadrature voltage component.
- the in-phase voltage component is filtered and amplified in the first filter and gain block 118 .
- the quadrature voltage component is filtered and amplified in the second filter and gain block 120 .
- the first ADC 124 generates a first digital data corresponding to an output of the first filter and gain block 118 .
- the second ADC 126 generates a second digital data corresponding to an output of the second filter and gain block 120 .
- the processor 130 processes the first digital data and the second digital data to estimate a distance of the target from the TOF system.
- the mixer I 114 and the mixer Q 116 provides an offset to the in-phase voltage component and quadrature phase component. This results in phase errors in the first digital data and the second digital data.
- the filter and gain block 118 and the filter and gain block 120 introduces gain error in the first digital data and the second digital data respectively.
- the receiver 100 also receives ambient light.
- the ambient light is due to one or more of the following, but not limited to, florescent lamps, sunlight, bulbs etc.
- the ambient light causes a direct current (DC) being generated in the receiver 100 .
- the receiver 100 processes this direct current through the mixer, filter and gain block and ADC. This current is cancelled in the processor 130 .
- ambient light conditions are above a threshold, it is required to cancel this direct current at the input.
- the receiver 100 does not provide a high dynamic range in a TOF system in the presence of ambient light.
- the direct current generated in the receiver 100 is 30 uA while an alternating current generated from the reflected light pulses is 100 pA.
- the receiver 100 is required to detect the 100 pA alternating current in presence of 30 uA direct current without reaching saturation.
- FIG. 2 illustrates a receiver 200 , according to an embodiment.
- the receiver 200 includes a photodiode 202 , an ambient cancellation circuit 208 , a coupling capacitor Cc 210 , a sigma delta analog to digital converter (ADC) 220 , a digital mixer 226 and a processor 230 .
- ADC sigma delta analog to digital converter
- the photodiode 202 includes a sensor 204 and an associated capacitance C D 206 .
- the ambient cancellation circuit 208 is coupled to the photodiode 202 .
- the coupling capacitor Cc 210 is coupled to the photodiode 202 .
- the sigma delta ADC 220 is coupled to the coupling capacitor Cc 210 .
- the sigma delta ADC 220 includes a first summer 212 , a loop filter 214 , a quantizer 216 and a digital to analog converter (DAC) 218 .
- the first summer 212 is coupled to the coupling capacitor Cc 210 .
- the loop filter 214 is coupled to the first summer 212 .
- the quantizer 216 is coupled to the loop filter 214 .
- the DAC 218 is coupled to the quantizer 216 .
- the digital mixer 226 is coupled to the quantizer 216 in the sigma delta ADC 220 .
- the processor 230 is coupled to the digital mixer 226 .
- the receiver 200 may include one or more additional components known to those skilled in the relevant art and are not discussed here for simplicity of the description.
- the receiver 200 in one example is used in a time-of-flight (TOF) system.
- the TOF system includes a light source that emits light pulses. The light pulses are emitted towards a target, which reflects the light pulses.
- the receiver 200 in the TOF system receives the reflected light pulses.
- the receiver 200 receives the reflected light pulses after a time of flight, which is proportional to a distance of the target from the TOF system.
- the sensor 204 in the photodiode 202 receives the reflected light pulses.
- the associated capacitance C D 206 stores a charge corresponding to the reflected light pulses.
- the photodiode 202 generates a current signal based on the reflected light pulses.
- the current signal includes a direct current (DC) signal.
- the DC signal is generated because of ambient light received by the photodiode 202 in the receiver 200 .
- the ambient light is due to one or more of the following, but not limited to, florescent lamps, sunlight, bulbs etc.
- the ambient cancellation circuit 208 cancels the DC signal in the current signal.
- a modulation signal is generated when the current signal is provided to the coupling capacitor Cc 210 .
- the modulation signal is provided to the sigma delta ADC 220 .
- the sigma delta ADC 220 generates a digital data in response to the modulation signal.
- the sigma delta ADC 220 is a band pass sigma delta ADC.
- the first summer 212 in the sigma delta ADC 220 generates an error signal in response to the modulation signal and a feedback current signal.
- the loop filter 214 filters the error signal to generate a filtered signal.
- the quantizer 216 quantizes the filtered signal to generate the digital data. In one version, the quantizer 216 is a 1 bit quantizer. This eases the node scaling requirements for the receiver 200 . Also, this creates a low power requirement for zero crossing detection in the quantizer 216 .
- the DAC 218 receives the digital data as a feedback signal.
- the DAC 218 generates the feedback current signal.
- the first summer 212 receives the feedback current signal from the DAC 218 . In one example, the first summer 212 subtracts the feedback current signal from the modulation signal to generate the error signal.
- the digital mixer 226 receives the digital data from the sigma delta ADC 220 .
- the digital mixer 226 generates an in-phase component (I) and a quadrature component (Q) corresponding to the digital data.
- the processor 230 processes the in-phase component and the quadrature component corresponding to the digital data.
- the processor 230 thereby estimates a distance of the target from the TOF system.
- the current signal is directly provided for processing and the processing in the sigma delta ADC 220 is performed on the modulation signal.
- a trans-impedance amplifier is not required as in the receiver 100 .
- the sigma delta ADC 220 generates the digital data; hence the mixing is performed digitally in the digital mixer 226 . This avoids any phase or gain errors that are prevalent when mixing is performed in analog domain such as in the receiver 100 .
- the sigma delta ADC 220 is a current input band pass sigma delta ADC which makes it a power efficient ADC.
- the ambient cancellation circuit 208 is separated from a circuit in the receiver 200 which processes the modulation signal. The ambient cancellation circuit 208 is capable of cancelling the DC signal in the current signal.
- the ambient cancellation circuit 208 provides a good low frequency ambient rejection and it also supports in relaxing the noise constraints of the receiver 200 .
- FIG. 3 illustrates an ambient cancellation circuit 300 , according to an embodiment.
- the ambient cancellation circuit 300 is analogous to the ambient cancellation circuit 208 (illustrated in FIG. 2 ) in connection and operation.
- the ambient cancellation circuit 300 is coupled to a photodiode 302 .
- the photodiode 302 is similar in connection and operation to the photodiode 202 .
- the ambient cancellation circuit 300 is also coupled to a coupling capacitor Cc 310 which is further coupled to a sigma delta ADC 320 .
- the coupling capacitor Cc 310 is analogous in connection and operation to the coupling capacitor Cc 210 .
- the sigma delta ADC 320 is similar in connection and operation to the sigma delta ADC 220 .
- the ambient cancellation circuit 300 includes a feedback circuit 305 and a first resistor R 1 324 .
- the feedback circuit 305 is coupled to the photodiode 302
- the first resistor R 1 324 is coupled between an output node 316 of the feedback circuit 305 and the photodiode 302 .
- the feedback circuit 305 includes a first operational amplifier 308 .
- the first operational amplifier 308 receives a first common mode voltage V CM1 304 at a first input port 312 .
- a second resistor R 2 306 is coupled between the photodiode 302 and a second input port 314 of the first operational amplifier 308 .
- a first capacitor C 1 322 is coupled between the second input port 314 of the first operational amplifier 308 and the output node 316 of the feedback circuit 305 .
- the output node 316 of the feedback circuit 305 receives an output of the first operational amplifier 308 .
- the ambient cancellation circuit 300 may include one or more additional components known to those skilled in the relevant art and are not discussed here for simplicity of the description.
- the photodiode 302 generates a current signal based on received light pulses.
- the current signal includes a direct current (DC) signal.
- the DC signal is generated because of ambient light received by the photodiode 302 .
- the ambient light is due to one or more of the following, but not limited to, florescent lamps, sunlight, bulbs etc.
- a voltage generated at the second input port 314 of the first operational amplifier 308 because of the DC signal is compared with the first common mode voltage V CM1 304 .
- a current noise generated because of a voltage noise (Vnoise) of the first operational amplifier 308 is given by
- I noise V noise/[ R 1 *(1+[ sC 1 R 2 ] ⁇ 1 ) ⁇ R 2] (1)
- the current noise generated is proportional to the associated capacitance C D 106 .
- the effect of voltage noise in the first operational amplifier 308 is scaled with the R 1 //R 2 resistor instead of the associated capacitance C D 106 in receiver 100 . This helps in relaxing the power specification of the first operational amplifier 308 . Also, appropriately choosing the first resistor R 1 324 and the second resistor R 2 306 would further reduce the noise generated by the first operational amplifier 308 .
- the first operational amplifier 308 is a low power and a low noise operational amplifier. As the DC signal is canceled at an input of a receiver (or a TOF receiver) and is not processed with the modulation signal, it results in high dynamic range of the receiver.
- the ambient cancellation circuit 300 provides a good low frequency ambient rejection and it also supports in relaxing the noise constraints of the receiver, for example receiver 200 .
- the ambient cancellation circuit 300 sets a bias of the photodiode 302 and cancels any out of band interferers.
- the ambient cancellation circuit 300 prevents saturation of the photodiode 302 .
- FIG. 4 illustrates a loop filter 400 , according to an embodiment.
- the loop filter 400 is analogous to the loop filter 214 (illustrated in FIG. 2 ) in connection and operation.
- the loop filter 400 is explained in connection with the receiver 200 illustrated in FIG. 2 .
- the loop filter 400 includes a continuous time resonator 406 , a second summer 410 , a discrete time resonator 416 and a third summer 420 .
- the continuous time resonator 406 receives an error signal 402 from a first summer similar to the first summer 212 .
- the second summer 410 is coupled to the continuous time resonator 406 .
- the discrete time resonator 416 is coupled to the second summer 410 , and the third summer 420 is coupled to the discrete time resonator 416 .
- the loop filter 400 may include one or more additional components known to those skilled in the relevant art and are not discussed here for simplicity of the description.
- the continuous time resonator 406 generates a low pass voltage V LP and a band pass voltage V BP in response to the error signal.
- the loop filter 400 utilizes anti-aliasing property of the continuous time resonator 406 .
- the second summer 410 receives the low pass voltage V LP and the band pass voltage V BP , and generates a summed voltage 412 .
- the second summer 410 sums the low pass voltage V LP and the band pass voltage V BP , to generate a summed voltage 412 .
- the discrete time resonator 416 generates a discrete voltage 418 in response to the summed voltage 412 .
- a transfer function of the discrete time resonator 416 is given by following equation.
- the discrete time resonator 416 provides band pass shaping to the summed voltage 412 to generate the discrete voltage 418 . Also, the band pass shaping provided by the discrete time resonator 416 is independent of process variations. In the above implementation, a center frequency of the discrete time resonator 416 is selected at Fs/4 to ease the processing requirement, for example, in the receiver 200 , where Fs is a sampling frequency.
- the third summer 420 receives the summed voltage 412 and the discrete voltage 418 , and generates a filtered output 424 . In one version, the third summer 420 sums the summed voltage 412 and the discrete voltage 418 to generate the filtered output 424 .
- the operation of each of the continuous time resonator 406 and the second summer 410 is further explained in detail in the subsequent paragraphs.
- FIG. 5 illustrates a continuous time resonator 500 , according to an embodiment.
- the continuous time resonator 500 is analogous to the continuous time resonator 406 (illustrated in FIG. 4 ) in connection and operation.
- the continuous time resonator 406 includes a second operational amplifier 506 and a third operational amplifier 520 .
- the second operational amplifier 506 receives a second common mode voltage V CM2 at a first input port 504 .
- a second input port 508 of the second operational amplifier 506 receives an error signal 502 (similar to the error signal 402 ).
- a second capacitor C 2 512 is coupled between the second input port 508 of the second operational amplifier 506 and a first output port 516 of the second operational amplifier 506 .
- the third operational amplifier 520 receives a third common mode voltage V CM3 528 at a first input port 522 .
- a third resistor R 3 532 is coupled between the first output port 516 of the second operational amplifier 506 and a second input port 524 of the third operational amplifier 520 .
- a third capacitor C 3 534 is coupled between the second input port 524 of the third operational amplifier 520 and a second output port 540 of the third operational amplifier 520 .
- a fourth resistor R 4 542 is coupled between the second input port 508 of the second operational amplifier 506 and the second output port 540 of the third operational amplifier 520 .
- the continuous time resonator 500 includes a negative feedback amplifier 536 coupled between the fourth resistor R 4 542 and the second output port 540 of the third operational amplifier 520 .
- the continuous time resonator 500 may include one or more additional components known to those skilled in the relevant art and are not discussed here for simplicity of the description.
- the second operational amplifier 506 integrates the error signal 502 to generate a band pass voltage V BP 544 .
- the band pass voltage V BP 544 is generated at the first output port 516 of the second operational amplifier 506 .
- the third operational amplifier 520 receives the band pass voltage V BP 544 .
- the third operational amplifier 520 integrates the band pass voltage V BP 544 to generate a low pass voltage V LP 550 .
- a noise contribution from the continuous time resonator 500 is highly dependent on the fourth resistor R 4 542 , the third resistor R 3 532 and the second capacitor C 2 512 .
- An input current noise has contributions from the second operational amplifier 506 , the fourth resistor R 4 542 and the third resistor R 3 532 .
- a contribution of noise from the fourth resistor R 4 542 is inversely proportional to a square root of the fourth resistor R 4 542 .
- a contribution of noise from the third resistor R 3 532 is directly proportional to a product of the second capacitor C 2 512 and a square root of the third resistor R 3 532 .
- a lower value of the second capacitor C 2 512 and the third resistor R 3 532 results in a lower noise.
- a corner frequency of the continuous time resonator 500 is defined as
- Corner ⁇ ⁇ Frequency 1 R ⁇ ⁇ 4 ⁇ R ⁇ ⁇ 3 ⁇ C ⁇ ⁇ 2 ⁇ C ⁇ ⁇ 3 ( 4 )
- the fourth resistor R 4 542 is scaled in accordance with a voltage swing constraints of the second operational amplifier 506 and the third operational amplifier 520 .
- a large DC signal would require a lower fourth resistor R 4 542 which increases the noise contribution as discussed above.
- a lower fourth resistor R 4 542 is compensated by increasing the third resistor R 3 532 , the second capacitor C 2 512 and the third capacitor C 3 534 , to maintain the corner frequency desired from the continuous time resonator 500 .
- Increasing the third resistor R 3 532 , the second capacitor C 2 512 and the third capacitor C 3 534 would increase the noise.
- the ambient cancellation circuit 208 is separated in the receiver 200 ; it removes the constraints of lower fourth resistor R 4 542 .
- Each of the fourth resistor R 4 542 , the third resistor R 3 532 , the second capacitor C 2 512 and the third capacitor C 3 534 is optimized to achieve best noise performance from the continuous time resonator 500 .
- FIG. 6 illustrates a summer 600 , according to an embodiment.
- the summer 600 is analogous to the second summer 410 (illustrated in FIG. 4 ) in connection and operation.
- the summer 600 is explained in connection with the loop filter 400 and the continuous time resonator 500 .
- the summer 600 includes a fourth operational amplifier 610 .
- the fourth operational amplifier 610 receives a fourth common mode voltage V CM4 at a first input port 602 .
- the fourth operational amplifier 610 generates a summed voltage V S 620 at a third output port 606 .
- a fourth capacitor C 4 616 is coupled between a second input port 604 of the fourth operational amplifier 610 and the second output port 540 of the third operational amplifier 520 .
- the fourth capacitor C 4 616 receives a low pass voltage V LP 612 from the continuous time resonator 500 .
- a fifth capacitor C 5 618 is coupled between the first input port 602 of the fourth operational amplifier 610 and the first output port 516 of the second operational amplifier 506 .
- the fifth capacitor C 5 618 receives a band pass voltage V BP 618 from the continuous time resonator 500 .
- a sixth capacitor C 6 622 and a fifth resistor R 5 624 are coupled between the second input port 604 of the fourth operational amplifier 610 and the third output port 606 of the fourth operational amplifier 610 .
- the band pass voltage V BP 618 and the low pass voltage V LP 612 are required to summed and gained with different coefficients. A large gain is required to be provided because of node scaling. Typically, the gains used for the band pass voltage V BP 618 and the low pass voltage V LP 612 are high to detect a low modulation signal received from the photodiode, for example photodiode 202 .
- the high gain means that an offset of the second operational amplifier 506 and the third operational amplifier 520 (in the continuous time resonator 500 ) are also gained to a high value. This can saturate later stages of the receiver 200 .
- the band pass voltage V BP 618 and the low pass voltage V LP 612 are provided high gain without increasing the offsets of the second operational amplifier 506 and the third operational amplifier 520 in the continuous time resonator 500 .
- the summer 600 is a capacitive summer.
- the summer 600 cancels any offsets provided by the second operational amplifier 506 and the third operational amplifier 520 .
- the summer 600 sums the band pass voltage V BP 618 and the low pass voltage V LP 612 to generate the summed voltage V S 620 .
- the summer 600 improves a dynamic range of a receiver for example the receiver 200 .
- FIG. 7 illustrates a time-of-flight (TOF) system 700 , according to an embodiment.
- the TOF system 700 includes a light source 702 , an amplifier 704 and a timing generator 706 .
- the amplifier 704 is coupled to the timing generator 706
- the light source 702 is coupled to the amplifier 704 .
- the light source 702 is an infrared (IR) light emitting diode (LED) that transmits IR light.
- IR infrared
- LED light emitting diode
- the TOF system 700 also includes a TOF sensor 712 .
- the TOF sensor 712 includes one or more TOF sensor pixels illustrated as 714 .
- Each TOF sensor pixel of the one or more TOF sensor pixels includes a receiver.
- the receiver is analogous to the receiver 200 in connection and operation.
- the TOF sensor 712 is coupled to a processor 720 , and each receiver in the TOF sensor 712 is coupled to the processor 720 .
- each receiver of the one or more receivers in a TOF sensor is associated with a processor (similar to receiver 200 ) and together these processors form processor 720 .
- one or more processors are coupled to the TOF sensor 712 .
- the processor 720 can be, for example, a CISC-type (Complex Instruction Set Computer) CPU, RISC-type CPU (Reduced Instruction Set Computer), or a digital signal processor (DSP).
- CISC-type Complex Instruction Set Computer
- RISC-type CPU Reduced Instruction Set Computer
- DSP digital signal processor
- the timing generator 706 generates a clock frequency.
- the light source 702 emits light pulses at the clock frequency.
- the light pulses emitted by the light source 702 are reflected from a target 710 to generate reflected light pulses.
- a photodiode associated with a receiver in the TOF sensor 712 receives the reflected light pulses.
- the receiver processes the reflected light pulses similar to the processing performed in the receiver 200 illustrated in FIG. 2 .
- the processor 720 process an in-phase component and a quadrature component received from a digital mixer associated with each receiver, to estimate a distance of the target 710 from the TOF system 700 .
- a trans-impedance amplifier is not required as in the receiver 100 .
- the requirement of building an accurate voltage at high modulating frequency using TIA is eliminated in the TOF system 700 . This helps in eliminating high power TIA and associated phase shift variation caused by TIA.
- the mixing is performed digitally in the digital mixer associated with each receiver.
- the sigma delta ADC used in the receiver is a current input band pass sigma delta ADC which makes it a power efficient ADC.
- the DC signal is canceled at an input of the receiver which results in high dynamic range of the receiver.
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Abstract
The disclosure provides a receiver with high dynamic range. The receiver includes a photodiode that generates a current signal. A coupling capacitor is coupled to the photodiode, and generates a modulation signal in response to the current signal received from the photodiode. A sigma delta analog to digital converter (ADC) is coupled to the coupling capacitor, and generates a digital data in response to the modulation signal. A digital mixer is coupled to the sigma delta ADC, and generates an in-phase component and a quadrature component corresponding to the digital data. A processor is coupled to the digital mixer, and processes the in-phase component and the quadrature component corresponding to the digital data.
Description
- This application claims priority from India provisional patent application No. 1245/CHE/2014 filed on Mar. 11, 2014 which is hereby incorporated by reference in its entirety.
- The present disclosure is generally related to time-of-flight (TOF) systems, and more particularly to achieving high dynamic range in a receiver associated with a TOF system.
- An emerging category of electronic devices is time-of-flight (TOF) systems. The TOF systems find applications in accelerometers, monolithic gyroscopes, light sensors, conveyor belts, depth sensing, proximity sensing, gesture recognition and imagers. A TOF system includes a light source that emits light pulses. The light pulses are emitted towards a target, which reflects the light pulses. The target is any object of interest which may include, but not limited to, a human, an automated component, an animal, an electronic device etc. A TOF sensor in the TOF system receives the reflected light pulses. The TOF sensor receives the reflected light pulses after a time of flight, which is proportional to a distance of the target from the TOF system.
- The TOF sensor includes one or more TOF sensor pixels. Each TOF sensor pixel includes a receiver. The receiver processes the reflected light pulses to estimate the distance of the target from the TOF system. In addition to the reflected light pulses, the receiver also receives other signals such as, but not limited to, electrical interferences, crosstalk signals and ambient light. The ambient light is due to one or more of the following, but not limited to, florescent lamps, sunlight, bulbs etc.
- The ambient light causes a direct current (DC) signal being generated in the receiver. A high DC signal saturates the receiver. This causes an error in estimating the distance of the target from the TOF system. In one example, a signal strength of the reflected light pulse is 30 dB whereas an interference generated is of the order of 100 dB. Thus, a receiver with high dynamic range is required.
- According to an aspect of the disclosure, a receiver is disclosed. The receiver includes a photodiode that generates a current signal. A coupling capacitor is coupled to the photodiode, and generates a modulation signal in response to the current signal received from the photodiode. A sigma delta analog to digital converter (ADC) is coupled to the coupling capacitor, and generates a digital data in response to the modulation signal. A digital mixer is coupled to the sigma delta ADC, and generates an in-phase component and a quadrature component corresponding to the digital data. A processor is coupled to the digital mixer, and processes the in-phase component and the quadrature component corresponding to the digital data.
-
FIG. 1 illustrates a receiver; -
FIG. 2 illustrates a receiver, according to an embodiment; -
FIG. 3 illustrates an ambient cancellation circuit, according to an embodiment; -
FIG. 4 illustrates a loop filter, according to an embodiment; -
FIG. 5 illustrates a continuous time resonator, according to an embodiment; -
FIG. 6 illustrates a summer, according to an embodiment; and -
FIG. 7 illustrates a time-of-flight (TOF) system, according to an embodiment. -
FIG. 1 illustrates areceiver 100. Thereceiver 100 includes aphotodiode 102, a trans-impedance amplifier (TIA) 110, amixer I 114, amixer Q 116, a first filter andgain block 118, a second filter andgain block 120, a first analog to digital converter (ADC) 124, a second analog to digital converter (ADC) 126 and aprocessor 130. - The
photodiode 102 includes asensor 104 and an associatedcapacitance C D 106. The TIA 110 is coupled to thephotodiode 102. The mixer I 114 and themixer Q 116 are coupled to the TIA 110. The first filter andgain block 118 is coupled to themixer I 114. The second filter andgain block 120 is coupled to themixer Q 116. - The first ADC 124 is coupled to the first filter and
gain block 118. The second ADC 126 is coupled to the second filter and gainblock 120. Theprocessor 130 is coupled to the first ADC 124 and the second ADC 126. - The operation of the
receiver 100 illustrated inFIG. 1 is explained now. The receiver in one example is used in a time-of-flight (TOF) system. The TOF system includes a light source that emits light pulses. The light pulses are emitted towards a target, which reflects the light pulses. Thereceiver 100 in the TOF system receives the reflected light pulses. Thereceiver 100 receives the reflected light pulses after a time of flight, which is proportional to a distance of the target from the TOF system. - The
sensor 104 in thephotodiode 102 receives the reflected light pulses. Theassociated capacitance C D 106 stores a charge corresponding to the reflected light pulses. The charge represents a modulated signal received by thephotodiode 102. The charge stored in the associatedcapacitance C D 106 is received by the TIA 110. TheTIA 110 demodulates the modulated signal to generate an in-phase voltage and a quadrature voltage. - The in-phase voltage is receiver by the
mixer I 114, and the quadrature voltage is received by themixer Q 116. Themixer I 114 multiplies the in-phase voltage and a voltage corresponding to the light pulses generated by the TOF system, to generate an in-phase voltage component. Themixer Q 116 multiplies the quadrature voltage and the voltage corresponding to the light pulses generated by the TOF system, to generate a quadrature voltage component. - The in-phase voltage component is filtered and amplified in the first filter and
gain block 118. The quadrature voltage component is filtered and amplified in the second filter and gainblock 120. The first ADC 124 generates a first digital data corresponding to an output of the first filter andgain block 118. Thesecond ADC 126 generates a second digital data corresponding to an output of the second filter and gainblock 120. - The
processor 130 processes the first digital data and the second digital data to estimate a distance of the target from the TOF system. The mixer I 114 and themixer Q 116 provides an offset to the in-phase voltage component and quadrature phase component. This results in phase errors in the first digital data and the second digital data. In addition, the filter and gainblock 118 and the filter and gainblock 120, introduces gain error in the first digital data and the second digital data respectively. - The
receiver 100 also receives ambient light. The ambient light is due to one or more of the following, but not limited to, florescent lamps, sunlight, bulbs etc. The ambient light causes a direct current (DC) being generated in thereceiver 100. Thereceiver 100 processes this direct current through the mixer, filter and gain block and ADC. This current is cancelled in theprocessor 130. However, when ambient light conditions are above a threshold, it is required to cancel this direct current at the input. - This is because if the direct current is cancelled by the
processor 130, a dynamic range of thereceiver 100 gets limited as it gets saturated by the direct current. Thus, thereceiver 100 does not provide a high dynamic range in a TOF system in the presence of ambient light. In one example, the direct current generated in thereceiver 100 is 30 uA while an alternating current generated from the reflected light pulses is 100 pA. Thus, thereceiver 100 is required to detect the 100 pA alternating current in presence of 30 uA direct current without reaching saturation. -
FIG. 2 illustrates areceiver 200, according to an embodiment. Thereceiver 200 includes aphotodiode 202, anambient cancellation circuit 208, a coupling capacitor Cc 210, a sigma delta analog to digital converter (ADC) 220, adigital mixer 226 and aprocessor 230. - The
photodiode 202 includes asensor 204 and an associatedcapacitance C D 206. Theambient cancellation circuit 208 is coupled to thephotodiode 202. The coupling capacitor Cc 210 is coupled to thephotodiode 202. Thesigma delta ADC 220 is coupled to the coupling capacitor Cc 210. Thesigma delta ADC 220 includes afirst summer 212, aloop filter 214, aquantizer 216 and a digital to analog converter (DAC) 218. - The
first summer 212 is coupled to the coupling capacitor Cc 210. Theloop filter 214 is coupled to thefirst summer 212. Thequantizer 216 is coupled to theloop filter 214. TheDAC 218 is coupled to thequantizer 216. - The
digital mixer 226 is coupled to thequantizer 216 in thesigma delta ADC 220. - The
processor 230 is coupled to thedigital mixer 226. Thereceiver 200 may include one or more additional components known to those skilled in the relevant art and are not discussed here for simplicity of the description. - The operation of the
receiver 200 illustrated inFIG. 2 is explained now. Thereceiver 200 in one example is used in a time-of-flight (TOF) system. The TOF system includes a light source that emits light pulses. The light pulses are emitted towards a target, which reflects the light pulses. Thereceiver 200 in the TOF system receives the reflected light pulses. Thereceiver 200 receives the reflected light pulses after a time of flight, which is proportional to a distance of the target from the TOF system. - The
sensor 204 in thephotodiode 202 receives the reflected light pulses. The associatedcapacitance C D 206 stores a charge corresponding to the reflected light pulses. Thephotodiode 202 generates a current signal based on the reflected light pulses. The current signal includes a direct current (DC) signal. The DC signal is generated because of ambient light received by thephotodiode 202 in thereceiver 200. The ambient light is due to one or more of the following, but not limited to, florescent lamps, sunlight, bulbs etc. - The
ambient cancellation circuit 208 cancels the DC signal in the current signal. A modulation signal is generated when the current signal is provided to the coupling capacitor Cc 210. The modulation signal is provided to thesigma delta ADC 220. Thesigma delta ADC 220 generates a digital data in response to the modulation signal. In one example, thesigma delta ADC 220 is a band pass sigma delta ADC. - The
first summer 212 in thesigma delta ADC 220 generates an error signal in response to the modulation signal and a feedback current signal. Theloop filter 214 filters the error signal to generate a filtered signal. Thequantizer 216 quantizes the filtered signal to generate the digital data. In one version, thequantizer 216 is a 1 bit quantizer. This eases the node scaling requirements for thereceiver 200. Also, this creates a low power requirement for zero crossing detection in thequantizer 216. TheDAC 218 receives the digital data as a feedback signal. TheDAC 218 generates the feedback current signal. Thefirst summer 212 receives the feedback current signal from theDAC 218. In one example, thefirst summer 212 subtracts the feedback current signal from the modulation signal to generate the error signal. - The
digital mixer 226 receives the digital data from thesigma delta ADC 220. Thedigital mixer 226 generates an in-phase component (I) and a quadrature component (Q) corresponding to the digital data. Theprocessor 230 processes the in-phase component and the quadrature component corresponding to the digital data. Theprocessor 230 thereby estimates a distance of the target from the TOF system. - In
receiver 200, the current signal is directly provided for processing and the processing in thesigma delta ADC 220 is performed on the modulation signal. Hence, a trans-impedance amplifier is not required as in thereceiver 100. Also, thesigma delta ADC 220 generates the digital data; hence the mixing is performed digitally in thedigital mixer 226. This avoids any phase or gain errors that are prevalent when mixing is performed in analog domain such as in thereceiver 100. - The
sigma delta ADC 220 is a current input band pass sigma delta ADC which makes it a power efficient ADC. In addition, theambient cancellation circuit 208 is separated from a circuit in thereceiver 200 which processes the modulation signal. Theambient cancellation circuit 208 is capable of cancelling the DC signal in the current signal. - As the DC signal is canceled at an input of the
receiver 200 and is not processed with the modulation signal, it results in high dynamic range of thereceiver 200. Theambient cancellation circuit 208 provides a good low frequency ambient rejection and it also supports in relaxing the noise constraints of thereceiver 200. -
FIG. 3 illustrates anambient cancellation circuit 300, according to an embodiment. Theambient cancellation circuit 300 is analogous to the ambient cancellation circuit 208 (illustrated inFIG. 2 ) in connection and operation. Theambient cancellation circuit 300 is coupled to aphotodiode 302. Thephotodiode 302 is similar in connection and operation to thephotodiode 202. - The
ambient cancellation circuit 300 is also coupled to acoupling capacitor Cc 310 which is further coupled to asigma delta ADC 320. Thecoupling capacitor Cc 310 is analogous in connection and operation to the coupling capacitor Cc 210. Thesigma delta ADC 320 is similar in connection and operation to thesigma delta ADC 220. - The
ambient cancellation circuit 300 includes afeedback circuit 305 and afirst resistor R1 324. Thefeedback circuit 305 is coupled to thephotodiode 302, and thefirst resistor R1 324 is coupled between anoutput node 316 of thefeedback circuit 305 and thephotodiode 302. - The
feedback circuit 305 includes a firstoperational amplifier 308. The firstoperational amplifier 308 receives a first commonmode voltage V CM1 304 at afirst input port 312. Asecond resistor R2 306 is coupled between thephotodiode 302 and asecond input port 314 of the firstoperational amplifier 308. - A
first capacitor C1 322 is coupled between thesecond input port 314 of the firstoperational amplifier 308 and theoutput node 316 of thefeedback circuit 305. Theoutput node 316 of thefeedback circuit 305 receives an output of the firstoperational amplifier 308. Theambient cancellation circuit 300 may include one or more additional components known to those skilled in the relevant art and are not discussed here for simplicity of the description. - The operation of the
ambient cancellation circuit 300 illustrated inFIG. 3 is explained now. Thephotodiode 302 generates a current signal based on received light pulses. The current signal includes a direct current (DC) signal. The DC signal is generated because of ambient light received by thephotodiode 302. The ambient light is due to one or more of the following, but not limited to, florescent lamps, sunlight, bulbs etc. - A voltage generated at the
second input port 314 of the firstoperational amplifier 308 because of the DC signal is compared with the first commonmode voltage V CM1 304. A current noise generated because of a voltage noise (Vnoise) of the firstoperational amplifier 308 is given by -
Inoise=Vnoise/[R 1*(1+[sC 1 R 2]−1)∥R2] (1) -
Inoise≈Snoise/(R 1 ∥R2) (2) - In
receiver 100, the current noise generated is proportional to the associatedcapacitance C D 106. Thus, the effect of voltage noise in the firstoperational amplifier 308 is scaled with the R1//R2 resistor instead of the associatedcapacitance C D 106 inreceiver 100. This helps in relaxing the power specification of the firstoperational amplifier 308. Also, appropriately choosing thefirst resistor R1 324 and thesecond resistor R2 306 would further reduce the noise generated by the firstoperational amplifier 308. - The first
operational amplifier 308 is a low power and a low noise operational amplifier. As the DC signal is canceled at an input of a receiver (or a TOF receiver) and is not processed with the modulation signal, it results in high dynamic range of the receiver. Theambient cancellation circuit 300 provides a good low frequency ambient rejection and it also supports in relaxing the noise constraints of the receiver, forexample receiver 200. - The
ambient cancellation circuit 300 sets a bias of thephotodiode 302 and cancels any out of band interferers. Theambient cancellation circuit 300 prevents saturation of thephotodiode 302. -
FIG. 4 illustrates aloop filter 400, according to an embodiment. Theloop filter 400 is analogous to the loop filter 214 (illustrated inFIG. 2 ) in connection and operation. Theloop filter 400 is explained in connection with thereceiver 200 illustrated inFIG. 2 . Theloop filter 400 includes acontinuous time resonator 406, asecond summer 410, adiscrete time resonator 416 and athird summer 420. - The
continuous time resonator 406 receives anerror signal 402 from a first summer similar to thefirst summer 212. Thesecond summer 410 is coupled to thecontinuous time resonator 406. Thediscrete time resonator 416 is coupled to thesecond summer 410, and thethird summer 420 is coupled to thediscrete time resonator 416. Theloop filter 400 may include one or more additional components known to those skilled in the relevant art and are not discussed here for simplicity of the description. - The operation of the
loop filter 400 illustrated inFIG. 4 is explained now. Thecontinuous time resonator 406 generates a low pass voltage VLP and a band pass voltage VBP in response to the error signal. Theloop filter 400 utilizes anti-aliasing property of thecontinuous time resonator 406. Thesecond summer 410 receives the low pass voltage VLP and the band pass voltage VBP, and generates a summedvoltage 412. In one example, thesecond summer 410 sums the low pass voltage VLP and the band pass voltage VBP, to generate a summedvoltage 412. - The
discrete time resonator 416 generates adiscrete voltage 418 in response to the summedvoltage 412. In one implementation, a transfer function of thediscrete time resonator 416 is given by following equation. -
- The
discrete time resonator 416 provides band pass shaping to the summedvoltage 412 to generate thediscrete voltage 418. Also, the band pass shaping provided by thediscrete time resonator 416 is independent of process variations. In the above implementation, a center frequency of thediscrete time resonator 416 is selected at Fs/4 to ease the processing requirement, for example, in thereceiver 200, where Fs is a sampling frequency. - The
third summer 420 receives the summedvoltage 412 and thediscrete voltage 418, and generates a filteredoutput 424. In one version, thethird summer 420 sums the summedvoltage 412 and thediscrete voltage 418 to generate the filteredoutput 424. The operation of each of thecontinuous time resonator 406 and thesecond summer 410 is further explained in detail in the subsequent paragraphs. -
FIG. 5 illustrates acontinuous time resonator 500, according to an embodiment. Thecontinuous time resonator 500 is analogous to the continuous time resonator 406 (illustrated inFIG. 4 ) in connection and operation. Thecontinuous time resonator 406 includes a secondoperational amplifier 506 and a thirdoperational amplifier 520. The secondoperational amplifier 506 receives a second common mode voltage VCM2 at afirst input port 504. Asecond input port 508 of the secondoperational amplifier 506 receives an error signal 502 (similar to the error signal 402). - A
second capacitor C2 512 is coupled between thesecond input port 508 of the secondoperational amplifier 506 and afirst output port 516 of the secondoperational amplifier 506. The thirdoperational amplifier 520 receives a third commonmode voltage V CM3 528 at afirst input port 522. Athird resistor R3 532 is coupled between thefirst output port 516 of the secondoperational amplifier 506 and asecond input port 524 of the thirdoperational amplifier 520. - A
third capacitor C3 534 is coupled between thesecond input port 524 of the thirdoperational amplifier 520 and asecond output port 540 of the thirdoperational amplifier 520. Afourth resistor R4 542 is coupled between thesecond input port 508 of the secondoperational amplifier 506 and thesecond output port 540 of the thirdoperational amplifier 520. - In one example, the
continuous time resonator 500 includes anegative feedback amplifier 536 coupled between thefourth resistor R4 542 and thesecond output port 540 of the thirdoperational amplifier 520. Thecontinuous time resonator 500 may include one or more additional components known to those skilled in the relevant art and are not discussed here for simplicity of the description. - The operation of the
continuous time resonator 500 illustrated inFIG. 5 is explained now. The secondoperational amplifier 506 integrates theerror signal 502 to generate a bandpass voltage V BP 544. The bandpass voltage V BP 544 is generated at thefirst output port 516 of the secondoperational amplifier 506. The thirdoperational amplifier 520 receives the bandpass voltage V BP 544. The thirdoperational amplifier 520 integrates the bandpass voltage V BP 544 to generate a lowpass voltage V LP 550. - A noise contribution from the
continuous time resonator 500 is highly dependent on thefourth resistor R4 542, thethird resistor R3 532 and thesecond capacitor C2 512. An input current noise has contributions from the secondoperational amplifier 506, thefourth resistor R4 542 and thethird resistor R3 532. - A contribution of noise from the
fourth resistor R4 542 is inversely proportional to a square root of thefourth resistor R4 542. Thus, a higher value of thefourth resistor R4 542 results in a lower noise. A contribution of noise from thethird resistor R3 532 is directly proportional to a product of thesecond capacitor C2 512 and a square root of thethird resistor R3 532. Thus, a lower value of thesecond capacitor C2 512 and thethird resistor R3 532 results in a lower noise. - A corner frequency of the
continuous time resonator 500 is defined as -
- To combat the direct current (DC) signal because of ambient light, the
fourth resistor R4 542 is scaled in accordance with a voltage swing constraints of the secondoperational amplifier 506 and the thirdoperational amplifier 520. A large DC signal would require a lowerfourth resistor R4 542 which increases the noise contribution as discussed above. - A lower
fourth resistor R4 542 is compensated by increasing thethird resistor R3 532, thesecond capacitor C2 512 and thethird capacitor C3 534, to maintain the corner frequency desired from thecontinuous time resonator 500. Increasing thethird resistor R3 532, thesecond capacitor C2 512 and thethird capacitor C3 534 would increase the noise. Since, theambient cancellation circuit 208 is separated in thereceiver 200; it removes the constraints of lowerfourth resistor R4 542. Each of thefourth resistor R4 542, thethird resistor R3 532, thesecond capacitor C2 512 and thethird capacitor C3 534 is optimized to achieve best noise performance from thecontinuous time resonator 500. -
FIG. 6 illustrates asummer 600, according to an embodiment. Thesummer 600 is analogous to the second summer 410 (illustrated inFIG. 4 ) in connection and operation. Thesummer 600 is explained in connection with theloop filter 400 and thecontinuous time resonator 500. Thesummer 600 includes a fourthoperational amplifier 610. The fourthoperational amplifier 610 receives a fourth common mode voltage VCM4 at afirst input port 602. The fourthoperational amplifier 610 generates a summedvoltage V S 620 at athird output port 606. - A
fourth capacitor C4 616 is coupled between asecond input port 604 of the fourthoperational amplifier 610 and thesecond output port 540 of the thirdoperational amplifier 520. Thefourth capacitor C4 616 receives a lowpass voltage V LP 612 from thecontinuous time resonator 500. Afifth capacitor C5 618 is coupled between thefirst input port 602 of the fourthoperational amplifier 610 and thefirst output port 516 of the secondoperational amplifier 506. - The
fifth capacitor C5 618 receives a bandpass voltage V BP 618 from thecontinuous time resonator 500. Asixth capacitor C6 622 and afifth resistor R5 624 are coupled between thesecond input port 604 of the fourthoperational amplifier 610 and thethird output port 606 of the fourthoperational amplifier 610. - The band
pass voltage V BP 618 and the lowpass voltage V LP 612 are required to summed and gained with different coefficients. A large gain is required to be provided because of node scaling. Typically, the gains used for the bandpass voltage V BP 618 and the lowpass voltage V LP 612 are high to detect a low modulation signal received from the photodiode, forexample photodiode 202. - The high gain means that an offset of the second
operational amplifier 506 and the third operational amplifier 520 (in the continuous time resonator 500) are also gained to a high value. This can saturate later stages of thereceiver 200. In thesummer 600, the bandpass voltage V BP 618 and the lowpass voltage V LP 612 are provided high gain without increasing the offsets of the secondoperational amplifier 506 and the thirdoperational amplifier 520 in thecontinuous time resonator 500. - The
summer 600 is a capacitive summer. Thesummer 600 cancels any offsets provided by the secondoperational amplifier 506 and the thirdoperational amplifier 520. Thesummer 600 sums the bandpass voltage V BP 618 and the lowpass voltage V LP 612 to generate the summedvoltage V S 620. Thesummer 600 improves a dynamic range of a receiver for example thereceiver 200. -
FIG. 7 illustrates a time-of-flight (TOF)system 700, according to an embodiment. TheTOF system 700 includes alight source 702, anamplifier 704 and atiming generator 706. Theamplifier 704 is coupled to thetiming generator 706, and thelight source 702 is coupled to theamplifier 704. In one example, thelight source 702 is an infrared (IR) light emitting diode (LED) that transmits IR light. - The
TOF system 700 also includes aTOF sensor 712. TheTOF sensor 712 includes one or more TOF sensor pixels illustrated as 714. Each TOF sensor pixel of the one or more TOF sensor pixels includes a receiver. The receiver is analogous to thereceiver 200 in connection and operation. - In one example, the
TOF sensor 712 is coupled to aprocessor 720, and each receiver in theTOF sensor 712 is coupled to theprocessor 720. In another example, each receiver of the one or more receivers in a TOF sensor is associated with a processor (similar to receiver 200) and together these processors formprocessor 720. - In yet another example, one or more processors are coupled to the
TOF sensor 712. Theprocessor 720 can be, for example, a CISC-type (Complex Instruction Set Computer) CPU, RISC-type CPU (Reduced Instruction Set Computer), or a digital signal processor (DSP). - The
timing generator 706 generates a clock frequency. Thelight source 702 emits light pulses at the clock frequency. The light pulses emitted by thelight source 702 are reflected from atarget 710 to generate reflected light pulses. A photodiode associated with a receiver in theTOF sensor 712 receives the reflected light pulses. - The receiver processes the reflected light pulses similar to the processing performed in the
receiver 200 illustrated inFIG. 2 . Theprocessor 720 process an in-phase component and a quadrature component received from a digital mixer associated with each receiver, to estimate a distance of thetarget 710 from theTOF system 700. - A trans-impedance amplifier (TIA) is not required as in the
receiver 100. The requirement of building an accurate voltage at high modulating frequency using TIA is eliminated in theTOF system 700. This helps in eliminating high power TIA and associated phase shift variation caused by TIA. The mixing is performed digitally in the digital mixer associated with each receiver. - This avoids any phase or gain errors that are prevalent when mixing is performed in analog domain such as in the
receiver 100. The sigma delta ADC used in the receiver is a current input band pass sigma delta ADC which makes it a power efficient ADC. In addition, the DC signal is canceled at an input of the receiver which results in high dynamic range of the receiver. - The foregoing description sets forth numerous specific details to convey a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention may be practiced without these specific details. Well-known features are sometimes not described in detail in order to avoid obscuring the invention. Other variations and embodiments are possible in light of above teachings, and it is thus intended that the scope of invention not be limited by this Detailed Description, but only by the following Claims.
Claims (20)
1. A receiver comprising:
a photodiode configured to generate a current signal;
a coupling capacitor coupled to the photodiode, and configured to generate a modulation signal in response to the current signal received from the photodiode;
a sigma delta analog to digital converter (ADC) coupled to the coupling capacitor and configured to generate a digital data in response to the modulation signal;
a digital mixer coupled to the sigma delta ADC and configured to generate an in-phase component and a quadrature component corresponding to the digital data; and
a processor coupled to the digital mixer and configured to process the in-phase component and the quadrature component corresponding to the digital data.
2. The receiver of claim 1 further comprising an ambient cancellation circuit coupled to the photodiode, wherein the ambient cancellation circuit comprising:
a feedback circuit coupled to the photodiode; and
a first resistor coupled between an output node of the feedback circuit and the photodiode.
3. The receiver of claim 2 , wherein the feedback circuit comprises:
a first operational amplifier configured to receive a first common mode voltage at a first input port;
a second resistor coupled between the photodiode and a second input port of the first operational amplifier; and
a first capacitor coupled between the second input port of the first operational amplifier and the output node of the feedback circuit, wherein the output node of the feedback circuit receives an output of the first operational amplifier.
4. The receiver of claim 1 , wherein the sigma delta ADC comprises:
a first summer coupled to the coupling capacitor and configured to generate an error signal in response to the modulation signal and a feedback current signal;
a loop filter coupled to the first summer and configured to filter the error signal to generate a filtered signal;
a quantizer coupled to the loop filter and configured to generate the digital data in response to the filtered signal; and
a digital to analog converter (DAC) configured to receive the digital data as a feedback signal and configured to generate the feedback current signal, wherein the first summer is configured to receive the feedback current signal from the DAC.
5. The receiver of claim 4 , wherein the loop filter comprises:
a continuous time resonator configured to generate a low pass voltage and a band pass voltage in response to the error signal;
a second summer coupled to the continuous time resonator and configured to receive the low pass voltage and the band pass voltage, the second summer configured to generate a summed voltage;
a discrete time resonator coupled to the second summer and configured to generate a discrete voltage in response to the summed voltage; and
a third summer coupled to the discrete time resonator, and configured to receive the summed voltage and the discrete voltage, the third summer configured to generate the filtered signal.
6. The receiver of claim 5 , wherein the continuous time resonator comprises:
a second operational amplifier configured to receive a second common mode voltage at a first input port, and configured to receive the error signal at a second input port, the second operational amplifier and configured to generate the band pass voltage at a first output port;
a second capacitor coupled between a second input port of the second operational amplifier and the first output port of the second operational amplifier;
a third operational amplifier configured to receive a third common mode voltage at a first input port, the third operational amplifier configured to generate the low pass voltage at a second output port;
a third capacitor coupled between a second input port of the third operational amplifier and the second output port of the third operational amplifier;
a third resistor coupled between the first output port of the second operational amplifier and the second input port of the third operational amplifier; and
a fourth resistor coupled between the second input port of the second operational amplifier and the second output port of the third operational amplifier.
7. The receiver of claim 5 , wherein the second summer comprises:
a fourth operational amplifier configured to receive a fourth common mode voltage at a first input port, the fourth operational amplifier configured to generate the summed voltage at a third output port;
a fourth capacitor coupled between the second output port of the third operational amplifier and a second input port of the fourth operational amplifier, the fourth capacitor configured to receive the low pass voltage;
a fifth capacitor coupled between the first output port of the second operational amplifier and the first input port of the fourth operational amplifier, the fifth capacitor configured to receive the band pass voltage;
a sixth capacitor coupled between the second input port of the fourth operational amplifier and the third output port of the fourth operational amplifier; and
a fifth resistor coupled between the second input port of the fourth operational amplifier and the third output port of the fourth operational amplifier.
8. The receiver of claim 1 , wherein the sigma delta ADC is a band pass sigma delta ADC.
9. A method comprising:
generating a current signal from reflected light pulses received by a photodiode, wherein the current signal comprises a direct current (DC) signal;
generating a modulation signal from the current signal;
generating a digital data in response to the modulation signal;
generating an in-phase component and a quadrature component corresponding to the digital data; and
processing the in-phase component and the quadrature component corresponding to the digital data.
10. The method of claim 9 further comprising cancelling the DC signal in an ambient cancellation circuit, the ambient cancellation circuit comprising:
a first operational amplifier configured to receive a first common mode voltage at a first input port;
a second resistor coupled between the photodiode and a second input port of the first operational amplifier;
a first capacitor coupled between the second input port of the first operational amplifier and an output node of the first operational amplifier; and
a first resistor coupled between the output node of the first operational amplifier and the photodiode.
11. The method of claim 9 , wherein generating the modulation signal is by providing the current signal to a coupling capacitor.
12. The method of claim 9 , wherein generating the digital data in response to the modulation signal comprises:
summing the modulation signal and a feedback current signal from a digital to analog converter (DAC) to generate an error signal;
filtering the error signal to generate a filtered signal; and
quantizing the filtered signal to generate the digital data, wherein the digital data is provided as a feedback signal to the DAC.
13. The method of claim 9 , wherein filtering the error signal comprises:
integrating the error signal to generate a band pass voltage;
integrating the band pass voltage to generate a low pass voltage;
summing the band pass voltage and the low pass voltage to generate a summed voltage;
generating a discrete voltage in response to the summed voltage; and
summing the discrete voltage and the summed voltage to generate the filtered signal.
14. A time-of-flight (TOF) system comprising:
a light source for emitting light pulses at a clock frequency;
a TOF sensor comprising one or more TOF sensor pixels, each TOF sensor pixel comprising a receiver, the receiver comprising:
a photodiode configured to generate a current signal from reflected light pulses, the light pulses emitted by the light source are reflected from a target to generate the reflected light pulses;
a coupling capacitor coupled to the photodiode, and configured to generate a modulation signal in response to the current signal received from the photodiode;
a sigma delta analog to digital converter (ADC) coupled to the coupling capacitor and configured to generate a digital data in response to the modulation signal; and
a digital mixer coupled to the sigma delta ADC and configured to generate an in-phase component and a quadrature component corresponding to the digital data;
a processor coupled to the TOF sensor and configured to process the in-phase component and the quadrature component received from the digital mixer in each receiver.
15. The TOF system of claim 14 further comprising an ambient cancellation circuit coupled to the photodiode, wherein the ambient cancellation circuit comprising:
a feedback circuit coupled to the photodiode; and
a first resistor coupled between an output node of the feedback circuit and the photodiode.
16. The TOF system of claim 15 , wherein the feedback circuit comprises:
a first operational amplifier configured to receive a first common mode voltage at a first input port;
a second resistor coupled between the photodiode and a second input port of the first operational amplifier; and
a first capacitor coupled between the second input port of the first operational amplifier and the output node of the feedback circuit, wherein the output node of the feedback circuit receives an output of the first operational amplifier.
17. The TOF system of claim 14 , wherein the sigma delta ADC comprises:
a first summer coupled to the coupling capacitor and configured to generate an error signal in response to the modulation signal and a feedback current signal;
a loop filter coupled to the first summer and configured to filter the error signal to generate a filtered signal;
a quantizer coupled to the loop filter and configured to generate the digital data in response to the filtered signal; and
a digital to analog converter (DAC) configured to receive the digital data as a feedback signal and configured to generate the feedback current signal, wherein the first summer is configured to receive the feedback current signal from the DAC.
18. The TOF system of claim 17 , wherein the loop filter comprises:
a continuous time resonator configured to generate a low pass voltage and a band pass voltage in response to the error signal;
a second summer coupled to the continuous time resonator and configured to receive the low pass voltage and the band pass voltage, the second summer configured to generate a summed voltage;
a discrete time resonator coupled to the second summer and configured to generate a discrete voltage in response to the summed voltage; and
a third summer coupled to the discrete time resonator, and configured to receive the summed voltage and the discrete voltage, the third summer configured to generate the filtered signal.
19. The TOF system of claim 18 , wherein the continuous time resonator comprises:
a second operational amplifier configured to receive a second common mode voltage at a first input port, the second operational amplifier configured to generate the band pass voltage at a first output port;
a second capacitor coupled between a second input port of the second operational amplifier and the first output port of the second operational amplifier;
a third operational amplifier configured to receive a third common mode voltage at a first input port, the third operational amplifier configured to generate the low pass voltage at a second output port;
a third capacitor coupled between a second input port of the third operational amplifier and the second output port of the third operational amplifier;
a third resistor coupled between the first output port of the second operational amplifier and the second input port of the third operational amplifier; and
a fourth resistor coupled between the second input port of the second operational amplifier and the second output port of the third operational amplifier.
20. The TOF system of claim 18 , wherein the second summer comprises:
a fourth operational amplifier configured to receive a fourth common mode voltage at a first input port, the fourth operational amplifier configured to generate the summed voltage at a third output port;
a fourth capacitor coupled between the second output port of the third operational amplifier and a second input port of the fourth operational amplifier, the fourth capacitor configured to receive the low pass voltage;
a fifth capacitor coupled between the first output port of the second operational amplifier and the first input port of the fourth operational amplifier, the fifth capacitor configured to receive the band pass voltage;
a sixth capacitor coupled between the second input port of the fourth operational amplifier and the third output port of the fourth operational amplifier; and
a fifth resistor coupled between the second input port of the fourth operational amplifier and the third output port of the fourth operational amplifier.
Priority Applications (2)
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US15/950,690 US10581451B2 (en) | 2014-03-11 | 2018-04-11 | Time-of-flight (TOF) receiver with high dynamic range comprising a digital mixer coupled to a sigma delta analog to digital converter |
US16/748,849 US11233525B2 (en) | 2014-03-11 | 2020-01-22 | Receiver and time-of-flight system with high dynamic range having a coupling capacitor respectively connected to a photodiode and a sigma delta analog to digital converter |
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IN1245/CHE/2014 | 2014-03-11 | ||
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US15/950,690 Continuation US10581451B2 (en) | 2014-03-11 | 2018-04-11 | Time-of-flight (TOF) receiver with high dynamic range comprising a digital mixer coupled to a sigma delta analog to digital converter |
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US20150260571A1 true US20150260571A1 (en) | 2015-09-17 |
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US14/644,308 Abandoned US20150260571A1 (en) | 2014-03-11 | 2015-03-11 | Time-of-flight (tof) receiver with high dynamic range |
US15/950,690 Active 2035-04-29 US10581451B2 (en) | 2014-03-11 | 2018-04-11 | Time-of-flight (TOF) receiver with high dynamic range comprising a digital mixer coupled to a sigma delta analog to digital converter |
US16/748,849 Active US11233525B2 (en) | 2014-03-11 | 2020-01-22 | Receiver and time-of-flight system with high dynamic range having a coupling capacitor respectively connected to a photodiode and a sigma delta analog to digital converter |
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US15/950,690 Active 2035-04-29 US10581451B2 (en) | 2014-03-11 | 2018-04-11 | Time-of-flight (TOF) receiver with high dynamic range comprising a digital mixer coupled to a sigma delta analog to digital converter |
US16/748,849 Active US11233525B2 (en) | 2014-03-11 | 2020-01-22 | Receiver and time-of-flight system with high dynamic range having a coupling capacitor respectively connected to a photodiode and a sigma delta analog to digital converter |
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Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2016191301A1 (en) * | 2015-05-22 | 2016-12-01 | Texas Instruments Incorporated | High speed illumination driver for tof applications |
US20180012922A1 (en) * | 2015-01-06 | 2018-01-11 | Huf Hüisbeck & Fürst GmbH & Co. KG | Optical device for exposure of a sensor device for a vehicle |
CN108631754A (en) * | 2018-04-27 | 2018-10-09 | 成都仕芯半导体有限公司 | A kind of high-precision phase shifting equipment |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
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KR20220166109A (en) | 2021-06-09 | 2022-12-16 | 에스케이하이닉스 주식회사 | I-tof pixel circuits for background light suprression |
US12015427B2 (en) | 2022-04-05 | 2024-06-18 | Stmicroelectronics (Research & Development) Limited | Photodiode current compatible input stage for a sigma-delta analog-to-digital converter |
US20230375679A1 (en) * | 2022-05-17 | 2023-11-23 | Stmicroelectronics (Research & Development) Limited | Quantum film direct time of flight sensor circuit for low cost short wave infrared operation |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20100271522A1 (en) * | 2009-04-28 | 2010-10-28 | Panasonic Corporation | Solid-state imaging device |
US20120177386A1 (en) * | 2011-01-10 | 2012-07-12 | At&T Intellectual Property I, L.P. | Electronic phase conjugation for impairment compensation in a fiber communication system |
US20130242283A1 (en) * | 2012-03-16 | 2013-09-19 | Advanced Scientific Concepts, Inc. | Personal ladar sensor |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4857928A (en) * | 1988-01-28 | 1989-08-15 | Motorola, Inc. | Method and arrangement for a sigma delta converter for bandpass signals |
US5442353A (en) * | 1993-10-25 | 1995-08-15 | Motorola, Inc. | Bandpass sigma-delta analog-to-digital converter (ADC), method therefor, and receiver using same |
-
2015
- 2015-03-11 US US14/644,308 patent/US20150260571A1/en not_active Abandoned
-
2018
- 2018-04-11 US US15/950,690 patent/US10581451B2/en active Active
-
2020
- 2020-01-22 US US16/748,849 patent/US11233525B2/en active Active
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20100271522A1 (en) * | 2009-04-28 | 2010-10-28 | Panasonic Corporation | Solid-state imaging device |
US20120177386A1 (en) * | 2011-01-10 | 2012-07-12 | At&T Intellectual Property I, L.P. | Electronic phase conjugation for impairment compensation in a fiber communication system |
US20130242283A1 (en) * | 2012-03-16 | 2013-09-19 | Advanced Scientific Concepts, Inc. | Personal ladar sensor |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20180012922A1 (en) * | 2015-01-06 | 2018-01-11 | Huf Hüisbeck & Fürst GmbH & Co. KG | Optical device for exposure of a sensor device for a vehicle |
US10692912B2 (en) * | 2015-01-06 | 2020-06-23 | Huf Hülsbeck & Fürst Gmbh & Co. Kg | Optical device for exposure of a sensor device for a vehicle |
WO2016191301A1 (en) * | 2015-05-22 | 2016-12-01 | Texas Instruments Incorporated | High speed illumination driver for tof applications |
US10073167B2 (en) | 2015-05-22 | 2018-09-11 | Texas Instruments Incorporated | High speed illumination driver for TOF applications |
CN108631754A (en) * | 2018-04-27 | 2018-10-09 | 成都仕芯半导体有限公司 | A kind of high-precision phase shifting equipment |
Also Published As
Publication number | Publication date |
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US20200162097A1 (en) | 2020-05-21 |
US10581451B2 (en) | 2020-03-03 |
US11233525B2 (en) | 2022-01-25 |
US20180234107A1 (en) | 2018-08-16 |
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