A circuit and method for converting charge or current into digital value

Abstract

The present invention discloses a circuit and method for converting a charge or current into a digital value, and relates to the technical field of electronic circuits. The present invention includes: a sampling circuit and an amplifying circuit: a photodiode PD, the photodiode PD is connected in parallel with a reset switch S2; a sampling switch S1, the sampling switch S1 is connected to the positive electrode of the photodiode PD; an embedded programmable gain amplifier PGA, the output end of the embedded programmable gain amplifier PGA is connected to an analog-to-digital converter ADC; the photodiode PD is connected in parallel with the reset switch S2 and then connected in series with one end of the sampling switch S1, and the other end of the sampling switch S1 is connected to the input end 1 of the embedded programmable gain amplifier PGA. When the input light intensity is very small, the circuit has good linearity, can meet the periodic sampling and conversion of the incident light intensity, and completely remove the incident light in the non-sampling period, which interferes with the sampling result.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic circuits, and in particular relates to a circuit and method for converting electric charge or current into digital values. Background Art

[0002] In the application of light sensors, the incident light intensity needs to be converted into a corresponding digital value. In the input circuit of a traditional light sensor, the photodiode PD converts the incident light into a current, which is amplified or integrated by the PGA. The amplified voltage or current is sent to the ADC and converted into a digital value.

[0003] The disadvantage of the input circuit of the traditional light sensor is that the circuit cannot work when some applications require only collecting the incident light intensity over a period of time.

[0004] For example, Chinese patent CN115002361A discloses a digital integral charge-to-digital conversion circuit and a photodetector digital pixel circuit, in particular, a digital integral charge-to-digital conversion circuit that increases charge storage capacity and improves linearity. The circuit is composed of an injection tube / current source, an integral capacitor, a reset switch, a comparator, a monostable circuit, a counter, a control signal generating circuit, a charge storage switch, a charge transfer switch and a unit charge storage capacitor. By using a unit charge storage capacitor and two switches connected thereto, when the current is integrated to trigger the comparator to flip, the unit charge Qo is used to supplement the charge discharged on the integral capacitor, replacing the traditional digital integration method of resetting the voltage, avoiding the influence of the comparator judgment voltage and delay time, and improving the linearity of the charge-to-digital conversion. Another example is Chinese patent CN108206698A, which relates to an ambient light sensor integral charge-balanced analog-to-digital converter and control method, including: an integrator circuit, a comparator, a current reference circuit, a bandgap voltage reference circuit, a counter, a digital logic control circuit, and a clock circuit. The range of the analog-to-digital converter is changed by controlling the magnitude of the integrator input current in the access circuit under different conditions, thereby improving the simulation speed and accuracy of the overall circuit. An ambient light sensor integral charge-balanced analog-to-digital converter and control method are proposed. The simulation accuracy of the charge-balanced analog-to-digital converter can reach 16bit, and the overall error is less than 0.5%, which can improve the conversion speed and conversion accuracy.

[0005] The sampling and conversion method proposed in the present invention can meet the requirements of periodic sampling and conversion of incident light intensity, and completely eliminate the interference of incident light in non-sampling periods on the sampling results. Summary of the invention

[0006] The purpose of the present invention is to provide a circuit and method for converting charge or current into a digital value. The circuit is composed of a photodiode PD, a variable capacitor CB, a switch, an embedded programmable gain amplifier PGA and an ADC, which solves the problem that the existing circuit cannot work when some applications require only collecting the incident light intensity within a period of time.

[0007] To solve the above technical problems, the present invention is achieved through the following technical solutions:

[0008] As one aspect provided by the present invention, the present invention is a circuit for converting a charge or current into a digital value, including a sampling circuit and an amplifying circuit:

[0009] The sampling circuit includes:

[0010] A photodiode PD, wherein the photodiode PD is connected in parallel with the reset switch S2;

[0011] A sampling switch S1, wherein the sampling switch S1 is connected to the positive electrode of the photodiode PD;

[0012] A sampling switch S1 and a reset switch S2 are added to the photodiode PD. When unwanted light is incident on the photodiode PD, the reset switch S2 is turned on to release the charge on the photodiode PD to avoid affecting the charge accuracy during sampling.

[0013] When the required light intensity is incident on the photodiode PD, the reset switch S2 is opened, the sampling switch S1 is closed, and the current generated on the photodiode PD is amplified or integrated by the PGA, thereby completing the sampling of the light intensity to voltage or current.

[0014] The amplifier circuit includes:

[0015] An embedded programmable gain amplifier PGA, wherein an output end of the embedded programmable gain amplifier PGA is connected to an analog-to-digital converter ADC;

[0016] The photodiode PD is connected in parallel with the reset switch S2 and then connected in series with one end of the sampling switch S1 , and the other end of the sampling switch S1 is connected to the input end 1 of the embedded programmable gain amplifier PGA.

[0017] It can meet the periodic sampling and conversion of the incident light intensity and completely remove the interference of the incident light in the non-sampling period on the sampling result.

[0018] Furthermore, the analog-to-digital converter ADC is connected to the data output terminal.

[0019] Furthermore, after the photodiode PD is connected in parallel with the reset switch S2 , the cathode of the photodiode PD is connected to the GND terminal.

[0020] Furthermore, it also includes a variable capacitor CB, and a reset switch S2' is connected in parallel to the variable capacitor CB; after the variable capacitor CB is connected in parallel with the reset switch S2', one end is connected to the second input terminal of the embedded programmable gain amplifier PGA through the sampling switch S1', and the other end is connected to the cathode of the photodiode PD.

[0021] Furthermore, the variable capacitor CB is connected to the reset switch S2 ′ in parallel, and one end connected to the photodiode PD is connected to the GND end.

[0022] Furthermore, a noise reduction circuit is included, and the sampling switch S1 and the sampling switch S1' are respectively connected to the input terminal 1 and the input terminal 2 of the embedded programmable gain amplifier PGA through the noise reduction circuit.

[0023] Furthermore, the noise reduction circuit is a CHOP or Auto Zero circuit.

[0024] As another aspect of the present invention, a method for converting charge or current into a digital value is provided, wherein the method is implemented based on the system for converting charge or current into a digital value as described in the first aspect.

[0025] Further, the following steps are included:

[0026] When unwanted light is incident on the photodiode PD, the reset switch S2 is turned on to release the charge on the photodiode PD;

[0027] When the required light intensity is incident on the photodiode PD, the reset switch S2 is opened, the sampling switch S1 is closed, and the current generated on the photodiode PD is amplified or integrated by the embedded programmable gain amplifier PGA;

[0028] Complete the sampling of light intensity to voltage or current.

[0029] Furthermore, the method further comprises the following steps:

[0030] Eliminate parasitic charges through a CHOP or Auto Zero circuit connected between the embedded programmable gain amplifier PGA and the sampling switch S1;

[0031] The variable capacitor CB is adjusted to offset the charge injection generated on the reset switch S2 ′ and the sampling switch S1 ′ and the charge injection generated on the sampling switch S1 and the reset switch S2 .

[0032] The present invention has the following beneficial effects:

[0033] When unwanted light is incident on the PD, S2 is turned on to release the charge on the PD to avoid affecting the charge accuracy during sampling; when the required light intensity is incident on the PD, S2 is disconnected and S1 is closed, and the current generated on the PD is amplified or integrated by the PGA, thereby completing the sampling of light intensity to voltage or current;

[0034] The offset of PGA itself will generate a large parasitic charge on the reset PD. In order to eliminate this parasitic charge, a CHOP or Auto Zero circuit is added in front of PGA.

[0035] Through the variable capacitor CB, S1' and S2', the charge injection generated on the switches S1' and S2' can be offset by the charge injection generated on the switches S1 and S2 by adjusting CB appropriately, thus offsetting the charge injection effect of the switches S1 and S2. Finally, the output of the PGA is quantized by the ADC to obtain a digital value of the net signal light intensity.

[0036] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0038] Figure 1 A circuit diagram for converting electric charge or current into digital value according to the present invention;

[0039] Figure 2 This is a simulation display diagram of the present invention. DETAILED DESCRIPTION

[0040] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0041] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0042] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0043] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0044] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0045] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0046] Embodiment 1:

[0047] See also Figure 1 As shown, as an embodiment provided by the present invention, the present invention is a circuit for converting charge or current into a digital value, including a sampling circuit and an amplifying circuit, the sampling circuit and the amplifying circuit include a photodiode PD, a variable capacitor CB, a switch, an embedded programmable gain amplifier PGA and an analog-to-digital converter ADC, the accumulated charge or current on the photodiode PD is injected into the embedded programmable gain amplifier PGA through the switch, the embedded programmable gain amplifier PGA amplifies the current or integrates it, and converts it into a digital output using the analog-to-digital converter ADC, the circuit can realize precise sampling and conversion of the signal generated by the photodiode PD in a certain period of time, and the present invention can also work well when the incident light intensity is very small or the sampling time is very short.

[0048] As an embodiment provided by the present invention, preferably, the sampling circuit includes:

[0049] A photodiode PD, wherein the photodiode PD is connected in parallel with the reset switch S2;

[0050] A sampling switch S1, wherein the sampling switch S1 is connected to the positive electrode of the photodiode PD;

[0051] The amplifier circuit includes:

[0052] An embedded programmable gain amplifier PGA, wherein an output end of the embedded programmable gain amplifier PGA is connected to an analog-to-digital converter ADC;

[0053] The photodiode PD is connected in parallel with the reset switch S2 and then connected in series with one end of the sampling switch S1. The other end of the sampling switch S1 is connected to the input end of the embedded programmable gain amplifier PGA (such as Figure 1 ).

[0054] A sampling switch S1 and a reset switch S2 are added to the photodiode PD. When unwanted light is incident on the photodiode PD, the reset switch S2 is turned on to release the charge on the photodiode PD to avoid affecting the charge accuracy during sampling.

[0055] When the required light intensity is incident on the photodiode PD, the reset switch S2 is opened, the sampling switch S1 is closed, and the current generated on the photodiode PD is amplified or integrated by the PGA, thereby completing the sampling of the light intensity to voltage or current.

[0056] As an embodiment provided by the present invention, preferably, the embedded programmable gain amplifier PGA and the analog-to-digital converter ADC can also be combined.

[0057] As an embodiment provided by the present invention, preferably, the analog-to-digital converter ADC is connected to the data output terminal.

[0058] As an embodiment provided by the present invention, preferably, after the photodiode PD is connected in parallel with the reset switch S2 , the cathode of the photodiode PD is connected to the GND terminal.

[0059] Embodiment 2:

[0060] See also Figure 1 As shown, as an embodiment provided by the present invention, the present invention is a circuit for converting charge or current into a digital value, based on the first embodiment, further comprising a variable capacitor CB, wherein a reset switch S2' is connected in parallel to the variable capacitor CB; after the variable capacitor CB is connected in parallel to the reset switch S2', one end is connected to the input terminal 2 (such as the input terminal 3 of the embedded programmable gain amplifier PGA) of the embedded programmable gain amplifier PGA through the sampling switch S1'. Figure 1 ), and the other end is connected to the cathode of the photodiode PD.

[0061] As an embodiment provided by the present invention, preferably, the variable capacitor CB is connected in parallel with the reset switch S2 ′ and then one end connected to the photodiode PD is connected to the GND end.

[0062] Embodiment three:

[0063] See also Figure 1 As shown, as an embodiment provided by the present invention, the present invention is a circuit for converting charge or current into a digital value. The offset of the embedded programmable gain amplifier PGA itself will generate a large parasitic charge on the reset PD. In order to eliminate this parasitic charge, a CHOP or Auto Zero circuit is added in front of the embedded programmable gain amplifier PGA.

[0064] As an embodiment provided by the present invention, preferably, based on the first and second embodiments, a noise reduction circuit is further included, and the sampling switch S1 and the sampling switch S1' are respectively connected to the input terminal 1 and the input terminal 2 of the embedded programmable gain amplifier PGA through the noise reduction circuit.

[0065] As an embodiment provided by the present invention, preferably, the noise reduction circuit is a CHOP or Auto Zero circuit.

[0066] Embodiment 4:

[0067] A method for converting charge or current into digital value. In order to offset the influence of charge injection of sampling switch S1 and reset switch S2, variable capacitor CB, sampling switch S1' and reset switch S2' are added. By properly adjusting variable capacitor CB, the charge injection generated on sampling switch S1' and reset switch S2' can be offset by the charge injection generated on sampling switch S1 and reset switch S2. Finally, the output of embedded programmable gain amplifier PGA is quantized by analog-to-digital converter ADC to obtain the digital value of net signal light intensity; the method described is implemented based on the system for converting charge or current into digital value described in embodiments one to three. A method for converting charge or current into digital value. The signal generated by photodiode PD in a certain period of time is precisely sampled and converted. When the incident light intensity is very small or the sampling time is very short, the present invention can also work well.

[0068] As an embodiment provided by the present invention, preferably, the following steps are included:

[0069] When unwanted light is incident on the photodiode PD, the reset switch S2 is turned on to release the charge on the photodiode PD;

[0070] When the required light intensity is incident on the photodiode PD, the reset switch S2 is opened, the sampling switch S1 is closed, and the current generated on the photodiode PD is amplified or integrated by the embedded programmable gain amplifier PGA;

[0071] Complete the sampling of light intensity to voltage or current.

[0072] As an embodiment provided by the present invention, preferably, the following steps are also included:

[0073] Eliminate parasitic charges through a CHOP or Auto Zero circuit connected between the embedded programmable gain amplifier PGA and the sampling switch S1;

[0074] The variable capacitor CB is adjusted to offset the charge injection generated on the reset switch S2 ′ and the sampling switch S1 ′ and the charge injection generated on the sampling switch S1 and the reset switch S2 .

[0075] like Figure 2 As shown in the figure, the simulation shows that the circuit has good linearity when the input light intensity is very small. Figure 2 In the figure, the horizontal axis is the input signal current, the vertical axis is the normalized equivalent output voltage, the input signal duty cycle is 1:100, and the full amplitude is 1000mV.

[0076] A circuit and method for converting charge or current into digital value. When unwanted light is incident on PD, S2 is turned on to release the charge on PD to avoid affecting the charge accuracy during sampling. When the required light intensity is incident on PD, S2 is turned off and S1 is closed. The current generated on PD is amplified or integrated by PGA, thereby completing the sampling of light intensity to voltage or current.

[0077] The offset of PGA itself will generate a large parasitic charge on the reset PD. In order to eliminate this parasitic charge, a CHOP or Auto Zero circuit is added in front of PGA.

[0078] Through the variable capacitor CB, S1' and S2', the charge injection generated on the switches S1' and S2' can be offset by the charge injection generated on the switches S1 and S2 by adjusting CB appropriately, thus offsetting the charge injection effect of the switches S1 and S2. Finally, the output of the PGA is quantized by the ADC to obtain a digital value of the net signal light intensity.

[0079] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0080] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A circuit for converting electric charge or current into a digital value, characterized in that: Including sampling circuit and amplification circuit: The sampling circuit includes: A photodiode PD, wherein the photodiode PD is connected in parallel with the reset switch S2; A sampling switch S1, wherein the sampling switch S1 is connected to the positive electrode of the photodiode PD; The amplifier circuit includes: An embedded programmable gain amplifier PGA, wherein an output end of the embedded programmable gain amplifier PGA is connected to an analog-to-digital converter ADC; The photodiode PD is connected in parallel with the reset switch S2 and then connected in series with one end of the sampling switch S1, and the other end of the sampling switch S1 is connected to the input end 1 of the embedded programmable gain amplifier PGA; It also includes a variable capacitor CB, which is connected in parallel with a reset switch S2'; after the variable capacitor CB is connected in parallel with the reset switch S2', one end is connected to the second input terminal of the embedded programmable gain amplifier PGA through the sampling switch S1', and the other end is connected to the cathode of the photodiode PD.

2. A circuit for converting charge or current into a digital value according to claim 1, characterized in that: The analog-to-digital converter ADC is connected to the data output terminal.

3. A circuit for converting a charge or current into a digital value according to claim 1, characterized in that: After the photodiode PD is connected in parallel with the reset switch S2 , the cathode of the photodiode PD is connected to the GND terminal.

4. The circuit for converting charge or current into digital value according to claim 1, characterized in that: The variable capacitor CB is connected in parallel with the reset switch S2 ′, and one end connected to the photodiode PD is connected to the GND end.

5. The circuit for converting charge or current into digital value according to claim 1, characterized in that: It also includes a noise reduction circuit. The sampling switch S1 and the sampling switch S1' are respectively connected to the input terminal 1 and the input terminal 2 of the embedded programmable gain amplifier PGA through the noise reduction circuit.

6. A circuit for converting charge or current into a digital value according to claim 5, characterized in that: The noise reduction circuit is a CHOP or Auto Zero circuit.

7. A method for converting electric charge or current into a digital value, characterized in that: The method is implemented based on a system for converting a charge or current into a digital value as described in any one of claims 1 to 6.

8. The method for converting electric charge or current into digital value according to claim 7, characterized in that: The following steps are involved: When unwanted light is incident on the photodiode PD, the reset switch S2 is turned on to release the charge on the photodiode PD; When the required light intensity is incident on the photodiode PD, the reset switch S2 is opened, the sampling switch S1 is closed, and the current generated on the photodiode PD is amplified or integrated by the embedded programmable gain amplifier PGA; Complete the sampling of light intensity to voltage or current.

9. The method for converting electric charge or current into digital value according to claim 8, characterized in that: The following steps are also included: Eliminate parasitic charges through a CHOP or Auto Zero circuit connected between the embedded programmable gain amplifier PGA and the sampling switch S1; The variable capacitor CB is adjusted to offset the charge injection generated on the reset switch S2 ′ and the sampling switch S1 ′ and the charge injection generated on the sampling switch S1 and the reset switch S2 .

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