CN115811670A - Differential amplifier and differential circuit based on image sensor - Google Patents
Differential amplifier and differential circuit based on image sensor Download PDFInfo
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- CN115811670A CN115811670A CN202211521059.6A CN202211521059A CN115811670A CN 115811670 A CN115811670 A CN 115811670A CN 202211521059 A CN202211521059 A CN 202211521059A CN 115811670 A CN115811670 A CN 115811670A
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Abstract
The invention discloses a differential amplifier and a differential circuit based on an image sensor, wherein the differential amplifier uses an open-loop gain mode and comprises input pair tubes, a load and a current source, output modules of two pixel units are used as input pair tubes at positive and negative ends of the differential amplifier, one end of each input pair tube is connected with the load of the differential amplifier, and the other end of each input pair tube is connected with the current source of the differential amplifier. The image sensor is used as a part of the differential circuit, the output module of the image sensor replaces the input geminate transistors of the original differential amplifier, the difference calculation of two paths of signals is directly realized, and the characteristics of row and column address selection of the current image sensor are combined, so that the method for calculating the difference of different pixel units in various image sensor arrays is provided, the area of the differential circuit is greatly reduced, and the power consumption and the complexity of the differential circuit are reduced.
Description
Technical Field
The invention belongs to the technical field of image sensors, and particularly relates to a differential amplifier and a differential circuit based on an image sensor.
Background
The image sensor is widely applied to the fields of military affairs, medical treatment, automobiles, mobile equipment and the like, in a traditional imaging mode, a core component of the image sensor is generally an imaging array formed by photosensitive detectors, the photosensitive detectors collect optical signals at different positions in a space, signals of all pixels are quantized by means of peripheral reading circuits, and imaging in a specified space range is achieved. However, as the resolution of the image sensor is increased, the data amount of a single image is increased rapidly, which puts a great pressure on the transmission bandwidth.
Patent CN2021105222018 proposes a novel imaging method, which collects a down-sampled image and a full-sampled gradient image, transmits the two images to a target terminal, and obtains a full-sampled original image through algorithm processing. The imaging mode is to compress a high-resolution high-bit-width image into a low-resolution high-bit-width data and a high-resolution low-bit-width data, so that the data volume participating in transmission is greatly reduced, and the problem of transmission of high-resolution and high-dynamic-range images is solved. The pixel values of the gradient image only need three states, which can be recorded as-1, 0 and +1, the required bit number is 2, and the size relationship of two adjacent pixels in the original image with high bit width is represented.
Therefore, the imaging method has the core work at the image sensor end that the difference of adjacent pixel signal quantities is realized in the reading and sampling circuit. The traditional circuit solves the difference value of the pixel unit of the image sensor, a reading circuit is needed to obtain pixel information in a voltage or current mode, and then a next-stage circuit is used for realizing the difference of pixel values, so that the method is a method for firstly collecting and then operating the image sensor by using a peripheral circuit. The circuit has high power consumption and complexity, occupies a large area, and is not beneficial to the small-size design of an image sensor end.
Disclosure of Invention
The purpose of the invention is as follows: in order to solve the problems in the prior art, the invention provides a differential amplifier and a differential circuit based on an image sensor, wherein the image sensor is used as a part of the differential circuit, an output module of the image sensor replaces the input end of the original differential amplifier, the difference operation of two paths of signals is directly realized, and the power consumption and the complexity of the differential circuit are effectively reduced.
The technical scheme is as follows: in order to achieve the above object, the present invention provides a differential amplifier based on an image sensor, for implementing a difference operation of output signals of two pixel units, the differential amplifier uses an open-loop gain mode, and includes input pair transistors, a load and a current source, the output modules of the two pixel units are used as input pair transistors of positive and negative ends of the differential amplifier, one end of the input pair transistor is connected to the load of the differential amplifier, and the other end is connected to the current source of the differential amplifier.
Further, the output module of the pixel unit comprises a reading transistor and a selection transistor.
Further, the readout transistor and the selection transistor of the pixel unit as a whole are denoted as an output module of the pixel unit.
The invention also provides a differential circuit based on the image sensor, which is used for realizing the difference operation of output signals of two columns of pixel units, the differential circuit is a differential amplifier using an open-loop gain mode and comprises input pair tubes, a load and a current source, output modules of the two columns of pixel units are used as input pair tubes at positive and negative ends of the differential amplifier, the output modules of each column of pixel units are in parallel connection, one end of each input pair tube is connected with the load of the differential amplifier, and the other end of each input pair tube is connected with the current source of the differential amplifier.
In addition, the differential circuit based on the image sensor is used for realizing the difference operation of output signals of the whole pixel array, the differential circuit comprises a plurality of differential amplifiers, the differential amplifiers use an open-loop gain mode and comprise input pair transistors, loads and current sources, an output module of each column of pixel units is used as an input pair transistor of the differential amplifier, the output modules of each column of pixel units are in parallel connection, one end of each input pair transistor is connected with the corresponding load, the other end of each input pair transistor is connected with the current source through a switch element, the current source is shared between the output modules of two adjacent columns of pixel units, a switch element is arranged between the loads of each column of pixel units, and the topological structure of the differential circuit is changed by adjusting the on-off of the switch element, so that the differential operation of the signal values of two columns of any adjacent pixels in the pixel array is realized.
Further, the switching element is a transistor having a switching function.
Has the beneficial effects that: the invention takes the image sensor as a part of the differential circuit, replaces the input geminate transistors of the original differential amplifier with the output module of the image sensor, directly realizes the difference calculation of two paths of signals, combines the row and column address selection characteristics of the current image sensor, provides a method for calculating difference values of different pixel units in various image sensor arrays, greatly reduces the area of the differential circuit and reduces the power consumption and the complexity of the differential circuit.
Drawings
FIG. 1 is a circuit diagram of a conventional five-transistor differential amplifier;
FIG. 2 is a circuit diagram of a differential amplifier based on a CMOS image sensor according to an embodiment of the present invention;
FIG. 3 is a circuit diagram of a differential amplifier based on a composite dielectric grid photosensitive detector according to an embodiment of the present invention;
FIG. 4 is a graph of the input and output curves of the differential amplifier of FIG. 3;
FIG. 5 is a circuit diagram illustrating a differential circuit with two columns of pixels in a pixel array as input terminals according to an embodiment of the present invention;
FIG. 6 is a circuit diagram of a differential circuit with an input terminal of the entire pixel array according to an embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. The advantages and features of the present invention will become more apparent from the following description.
The present embodiment is described using a standard five-transistor differential operational amplifier, and the load of the differential operational amplifier is a transistor.
As shown in FIG. 1, the N-type transistor M0 is a current source for adjusting the gate voltage V of M0 B0 The current of the current source can be adjusted. The N-type transistors M1 and M2 are two input pair transistors of the differential operational amplifier, wherein the gate of M1 is connected to the positive input voltage V +, and the gate of M2 is connected to the negative input voltage V-. The P-type transistor M3 and the P-type transistor M4 are respectively loads of the positive input tube M1 and the negative input tube M2, and gates of the M3 and the M4 are connected to a drain of the M3. The output voltage V of the five-tube differential operational amplifier OUT Comprises the following steps:
VOUT＝AV(V+-V-)，
wherein, V OUT Is the output voltage of the differential operational amplifier, A V Is the open loop gain of the differential operational amplifier, V + is the positive side input voltage and V-is the negative side input voltage.
For a CMOS Image Sensor (CIS), in order to obtain a difference between signal quantities of two pixels, a Source Follow (SF) transistor and a row select transistor in the CIS pixel may be used to replace an input tube in the differential operational amplifier.
As shown in fig. 2, N-type transistors M1 and M10 are an SF pipe and a row selection pipe of the CIS pixel unit 1, respectively, N-type transistors M2 and M20 are an SF pipe and a row selection pipe of the CIS pixel unit 2, respectively, and FD1 and FD2 represent Floating Diffusion (FD) nodes of the pixel unit 1 and the pixel unit 2, respectively. Compared with the standard five-transistor differential operational amplifier structure in fig. 1, in fig. 2, the SF transistor M1 and the row selection transistor M10 of the CIS pixel unit 1 replace the positive-end input transistor in fig. 1, and the SF transistor M2 and the row selection transistor M20 of the CIS pixel unit 2 replace the negative-end input transistor in fig. 1, so that the output voltage V of the differential amplifier OUT Comprises the following steps:
VOUT＝AV(VFD1-VFD2)，
wherein A is V Is the open loop gain, V, under selected conditions of the row select transistors M10 and M20 FD1 Is the FD node voltage, V, of the pixel cell 1 FD2 Is the FD node voltage of the pixel unit 2.
Since the voltage variation of the FD is substantially proportional to the signal collected by the CIS during the CIS reading operation, the differential amplifier directly achieves the purpose of subtracting the two pixel signal quantities.
However, the output terminal of the CIS pixel involves two transistors, and the structure is relatively complex, which is not favorable for the description in conjunction with the following preferred scheme, while the readout equivalent circuit diagram of the composite dielectric gate photosensitive detector in patent CN200910024504.6 or CN201610592997.3 can be regarded as a single floating gate device, and the optical signal quantity of the composite dielectric gate photosensitive detector is in a linear relationship with the threshold voltage. Therefore, the present embodiment is described below mainly in conjunction with a composite dielectric grid photosensitive detector.
Fig. 3 is a circuit diagram of a differential scheme using a composite dielectric gate photosensitive detector as an image sensor, in which N-type floating gate transistors M1 and M2 are respectively read-out modules of a pixel unit 1 and a pixel unit 2, and are respectively used as a positive input transistor and a negative input transistor of a differential operational amplifier, as in the CIS principle. Referring to the working characteristics of the composite dielectric gate photosensitive detector, in an unselected state, the grids of the N-type floating gate transistors M1 and M2 are connected with 0V; in the selected state, the gates of the N-type floating gate transistors M1 and M2 are connected to a suitable read voltage V Read Can be subjected to differential operation, then the voltage V is output OUT Comprises the following steps:
VOUT＝AVVRead-VT1-(VRead-VT2)＝-AV(VT1-VT2)，
AV＝gmn(ron||rop)，
wherein, V Read Is the read-out voltage applied to the grid electrode of the composite dielectric grid photosensitive detector in the selected state, A V Is the open loop gain, V, of the differential amplifier T1 Is the threshold voltage, V, of the pixel cell 1 T2 Is the threshold voltage, gm, of the pixel cell 2 n Is the transconductance of the N-type floating gate transistor, r on Is the on-resistance, r, of the N-type floating gate transistor op It is ron | rop which represents the value of two resistors connected in parallel.
V T2 ) Representing the difference between the input signals at the two ends, so that there is a positive voltage magnitude V img : when V is T1 -V T2 >V img When the voltage is zero, the output voltage is 0V; when V is T1 -V T2 <-V img Then, the output voltage is a voltage source voltage VCC; when-V img ≤V T1 -V T2 -AV (VT 1-VT 2). Here correspond to three states of a gradient image, and the open-loop gain a can be adjusted by adjusting physical parameters (such as gate length and gate width) of the P-type transistor and the N-type floating-gate transistor V And said voltage magnitude V img To match the requirements of the application.
FIG. 5 is a circuit diagram of a differential scheme with two columns of pixels in a pixel array at the input, 3 pixels per column, and pixels per columnThe drain ends are connected to form a bit line BL which is connected with the drain end of the P-type transistor used as a load; the source ends of the pixels in each column are connected to form a source line SL, and the source line SL is connected with the drain end of an N-type transistor M0 serving as a current source; the gates of the pixels in the same row are connected to form a word line WL. Applying the read voltage V using a word line WL of a time-selected row read If 0V is applied to unselected rows, only a selected one of all parallel pixels in the same column is in a conducting state, the circuit principle in the conducting state is simplified into fig. 3, and the difference between two pixel signal values of any row and adjacent column of the pixel array of the image sensor can be selectively output.
Fig. 6 is a schematic diagram of a multi-differential amplifier circuit with the input terminal of the entire pixel array, and the pixel array is connected in the same manner as described in fig. 5. On the basis, the source line SL of the ith column of pixels i Respectively passing through two N-type switch transistors and current source transistors M0 at two sides i-1 And M0 i Is connected, wherein i is a positive integer. And the bit line BL of the ith column i And a P-type load transistor M3 i Is connected to the drain terminal of the load transistor M3 i Gate of and adjacent column load transistor M3 i-1 Or M3 i+1 Are connected via a switching transistor.
Every other column of the output ends of the multi-differential amplifying circuit of the pixel array is arranged, for example, the bit line BL of the ith column i Set the output end V Oi (i.e., load transistor M3) i Drain of) then adjacent bit line BL i-1 And BL i+1 No output terminal is provided, and the load transistor M3 i-1 And M3 i+1 Respectively with respective load transistors M3 i-1 And M3 i+1 Are connected. Under the connection condition, the difference circuit of the image sensor pixel array can realize the difference of pixel values of two adjacent columns in any row in the array under the action of the switching transistor. For example:
(1) Word line WL 1 Applying the read voltage V Read ，V SO Applying a starting voltage, V SE And when the voltage is turned off, the output voltage is the difference value of the pixels in the (i-1) th column and the ith column in the 1 st row, namely:
VOi＝AV(VT1,i-VT(1,i-1))，
wherein, V T(1,i-1) Is the threshold voltage, V, of the row 1, column i-1 pixels T(1,i) Is the threshold voltage of the pixel in row 1, column i.
(2) Word line WL 2 Applying the sense voltage VRead, V SO Closing, V SE And applying a starting voltage, wherein the output voltage is the difference value of the pixels in the (i + 1) th column and the ith column in the 2 nd row, namely:
VOi＝AV(VT2,i-VT(2,i+1))，
wherein, V T(2,i+1) Is the threshold voltage, V, of the row 2, column i +1 pixels T(2,i) Is the threshold voltage of the row 2, column i pixel.
Moreover, under the conditions that all VSOs are turned on and all VSEs are turned off, the acquisition of a half differential value of the array can be realized; and under the conditions that all VSOs are closed and the VSEs are opened, the other half of differential values of the array can be acquired, and finally, the acquisition of the data of the whole gradient image is completed.
It should be noted that the embodiments in the present specification are described in a progressive manner, and each part is mainly described as different from the previous part, and the same and similar parts may be referred to each other.
The above description is only for the purpose of describing the preferred embodiments of the present invention and is not intended to limit the scope of the claims of the present invention, and any person skilled in the art can make possible the variations and modifications of the technical solutions of the present invention using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention, and therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention belong to the protection scope of the technical solutions of the present invention.
Claims (6)
1. The differential amplifier based on the image sensor is used for realizing the difference operation of output signals of two pixel units, and is characterized in that the differential amplifier uses an open-loop gain mode and comprises input pair tubes, a load and a current source, output modules of the two pixel units are used as input pair tubes of positive and negative ends of the differential amplifier, one end of each input pair tube is connected with the load of the differential amplifier, and the other end of each input pair tube is connected with the current source of the differential amplifier.
2. The differential amplifier of claim 1, wherein the output block of the pixel cell comprises a readout transistor and a select transistor.
3. A differential amplifier as claimed in claim 1 wherein said load comprises a resistor or a field effect transistor.
4. The differential circuit based on the image sensor is used for realizing the difference operation of output signals of two columns of pixel units, and is characterized in that the differential circuit is a differential amplifier using an open-loop gain mode and comprises input pair tubes, a load and a current source, output modules of the two columns of pixel units are used as input pair tubes at positive and negative ends of the differential amplifier, the output modules of each column of pixel units are connected in parallel, one end of each input pair tube is connected with the load of the differential amplifier, and the other end of each input pair tube is connected with the current source of the differential amplifier.
5. The differential circuit based on the image sensor is used for realizing the difference operation of output signals of the whole pixel array and is characterized by comprising a plurality of differential amplifiers, wherein the differential amplifiers use an open-loop gain mode and comprise input pair transistors, loads and current sources, an output module of each row of pixel units is used as an input pair transistor of the differential amplifier, the output modules of each row of pixel units are in parallel connection, one ends of the input pair transistors are connected with corresponding loads, the other ends of the input pair transistors are connected with the current sources through switch elements, the current sources are shared between the output modules of two adjacent rows of pixel units, the switch elements are arranged between the loads of each row of pixel units, and the topological structure of the differential circuit is changed by adjusting the on-off of the switch elements, so that the differential operation of the signal values of any two adjacent rows of pixels in the pixel array is realized.
6. A differential circuit as claimed in claim 5, wherein said switching element is a transistor having a switching action.
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