DC calibration pre-stage circuit

Abstract

The embodiment of the utility model provides a direct-current calibration pre-stage circuit which is provided with a modulation circuit, an alternating-current coupling circuit, a multiplication circuit and a low-pass filter circuit, and the modulation circuit is used for modulating an output signal of a signal source into a first square wave signal. A direct-current part in the first square wave signal is removed through an alternating-current coupling circuit, and an alternating-current part is reserved to obtain a second square wave signal, so that after the second square wave signal is multiplied by a second modulation signal through a multiplication circuit, the obtained product can be equivalent to the sum of products of a series of sine waves; the method comprises the following steps of: obtaining a series of frequency multiplication cosine signals, further enabling the frequency multiplication cosine signals to be equivalent to the sum of a direct-current signal which is in multiple relation with a direct-current part in an effective signal of a signal source and a series of frequency multiplication cosine signals, and filtering the frequency multiplication cosine signals through a low-pass filter circuit, thereby restoring the direct-current signal in the effective signal, removing a noise signal and realizing noise reduction and calibration processing on an output signal of the signal source.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of automated testing technology, and in particular to a direct current calibration pre-stage circuit. BACKGROUND

[0002] In the testing process of a chip such as a Liquid Crystal Display (LCD) chip or an Organic Light-Emitting Diode Display (OLED) chip, a test machine is provided with a large number of analog test signal output channels. In order to ensure the direct current precision of the output analog signal, a direct current calibration circuit with high precision and stability is usually integrated in the test machine to calibrate the direct current of the analog signal.

[0003] The current direct current calibration circuit generally includes a channel gating switch network, a pre-stage circuit, and an analog-to-digital conversion circuit. The pre-stage circuit is used to amplify, shape, filter, and the like, the input analog signal, and the noise amplitude in the output signal of the pre-stage circuit directly determines the upper limit of the effective resolution of the direct current calibration circuit.

[0004] In a common pre-stage circuit composed of an operational amplifier, the main components of low-frequency noise include the 1 / f noise of the operational amplifier, the 50 / 60 Hz power frequency noise, the temperature drift noise caused by the environmental temperature fluctuation, and the like. When the amplitude of the input analog signal is close to zero, the effective signal therein is easily affected by the low-frequency noise, and even the effective signal can be submerged in the noise, resulting in a low signal-to-noise ratio in the channel and the inability to extract the weak effective signal. CONTENT OF THE INVENTION

[0005] The present disclosure provides a direct current calibration pre-stage circuit which can restore the direct current signal in the effective signal of a signal source and remove the noise signal.

[0006] In one aspect of the present disclosure, a direct current calibration pre-stage circuit is provided, which includes a modulation circuit, an alternating current coupling circuit, a multiplication circuit, and a low-pass filter circuit.

[0007] At least two input ends of the modulation circuit are connected with an output end of a signal source and a ground end of the signal source respectively, and the modulation circuit is configured to alternately receive an effective level signal and a zero point level signal of the signal source based on a first modulation signal, so as to modulate the direct current signal output by the signal source into a first square wave signal.

[0008] An input end of the alternating current coupling circuit is connected with an output end of the modulation circuit, and the alternating current coupling circuit is configured to remove the direct current component in the first square wave signal and output a second square wave signal.

[0009] An input end of the multiplication circuit is connected with an output end of the AC coupling circuit, and the multiplication circuit is configured to multiply the second modulation signal with the second square wave signal;

[0010] An input end of the low-pass filter circuit is connected with an output end of the multiplication circuit, and the low-pass filter circuit is configured to filter a frequency-doubled cosine signal in an output signal of the multiplication circuit and output a target DC signal;

[0011] The multiplication of the second modulation signal and the second square wave signal is equivalent to a sum of the target DC signal and the frequency-doubled cosine signal, and an amplitude of the target DC signal is in a multiple relationship with an amplitude of a DC signal in the effective level signal.

[0012] Optionally, the modulation circuit is provided with a first single-pole double-throw switch, and the at least two input ends of the modulation circuit include a first static contact and a second static contact of the first single-pole double-throw switch;

[0013] The first static contact is connected with an output end of the signal source, and the second static contact is connected with a ground end of the signal source, and a moving contact of the first single-pole double-throw switch is connected with the first static contact when the first modulation signal is at a high level, and is connected with the second static contact when the first modulation signal is at a low level.

[0014] Optionally, the modulation circuit is provided with an amplifier, an input end of the amplifier is connected with the moving contact of the first single-pole double-throw switch, and an output end of the amplifier is connected with an input end of the AC coupling circuit, and the amplifier is configured to perform amplitude adjustment and signal buffering on a received level signal.

[0015] Optionally, a signal frequency of the first modulation signal is outside a preset frequency range, the preset frequency range includes a signal frequency of low-frequency noise and an integer multiple of the signal frequency of the low-frequency noise, and the low-frequency noise includes at least one of 1 / f noise, power frequency noise and temperature drift noise.

[0016] Optionally, the AC coupling circuit is provided with a capacitor, and the capacitor is configured to transmit an AC component in the first square wave signal and block a DC component in the first square wave signal.

[0017] Optionally, the multiplication circuit is provided with a second single-pole double-throw switch and an operational amplifier;

[0018] A moving contact of the second single-pole double-throw switch is connected with a non-inverting input end of the operational amplifier, and two static contacts of the second single-pole double-throw switch are respectively connected with a ground end and an output end of the AC coupling circuit;

[0019] The second single-pole double-throw switch is configured to switch the connection relationship between the moving contact and the two stationary contacts based on the second modulation signal, so as to multiply the second modulation signal and the second square wave signal through the operational amplifier.

[0020] Optionally, the first modulation signal and the second modulation signal are square wave signals with the same frequency and the same phase.

[0021] When the moving contact of the second single-pole double-throw switch is connected with the stationary contact of the ground terminal, the second square wave signal is input into the operational amplifier through the inverting input terminal of the operational amplifier, and the output signal of the multiplication circuit is the product of the second square wave signal and a signal with a first preset amplitude.

[0022] When the moving contact of the second single-pole double-throw switch is connected with the stationary contact corresponding to the output terminal of the alternating current coupling circuit, the second square wave signal is input into the operational amplifier through the non-inverting input terminal of the operational amplifier, and the output signal of the multiplication circuit is the product of the second square wave signal and a signal with a second preset amplitude, the first preset amplitude and the second preset amplitude being opposite to each other.

[0023] Optionally, the output terminal of the low-pass filter circuit is connected with an analog-to-digital conversion circuit, and the analog-to-digital conversion circuit is configured to encode the received analog signal into a digital signal.

[0024] According to the embodiments of the present disclosure, by arranging the modulation circuit, the alternating current coupling circuit, the multiplication circuit and the low-pass filter circuit in the direct current calibration pre-stage circuit, the output signal of the signal source is modulated into a first square wave signal by the modulation circuit, then the direct current part in the first square wave signal is removed by the alternating current coupling circuit, and the alternating current part is obtained as a second square wave signal, so that after the second square wave signal is multiplied with a second modulation signal by the multiplication circuit, the product obtained can be equivalent to the sum of a series of sine wave products, and further equivalent to a direct current signal in a multiple relationship with the direct current part in the effective signal of the signal source and the sum of a series of frequency multiplication cosine signals, and then the frequency multiplication cosine signals are filtered out by the low-pass filter circuit, so that the direct current signal in the effective signal can be restored, the noise signal is removed, and the noise reduction processing of the output signal of the signal source is realized.

[0025] The technical solutions of the present disclosure will be further described in detail below by means of the accompanying drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings, which form a part of the specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0027] Referring to the drawings, the present disclosure can be more clearly understood in light of the following detailed description, in which:

[0028] Figure 1 A structure diagram of a direct current calibration pre-stage circuit provided for an exemplary embodiment of the present disclosure is shown in FIG. 1.

[0029] Figure 2 A structure diagram of a modulation circuit provided for an exemplary embodiment of the present disclosure is shown in FIG. 2.

[0030] Figure 3 A structure diagram of an alternating current coupling circuit provided for an exemplary embodiment of the present disclosure is shown in FIG. 3.

[0031] Figure 4 A structure diagram of a multiplication circuit provided for an exemplary embodiment of the present disclosure is shown in FIG. 4.

[0032] Figure 5 A structure diagram of a direct current calibration pre-stage circuit provided for another exemplary embodiment of the present disclosure is shown in FIG. 5.

[0033] The reference signs are as follows:

[0034] Signal source-1; modulation circuit-2; alternating current coupling circuit-3; multiplication circuit-4; low-pass filter circuit-5; analog-to-digital conversion circuit-6.

[0035] First single-pole double-throw switch-21; first amplifier-22; capacitor-31; second amplifier-32; second single-pole double-throw switch-41; operational amplifier-42. DETAILED DESCRIPTION

[0036] Various exemplary embodiments of the present disclosure will now be described in detail below with reference to the accompanying drawings. It should be noted that the relative arrangement, numerical expressions, and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present disclosure unless specifically stated otherwise.

[0037] Those skilled in the art can understand that the terms "first", "second", and the like in the embodiments of the present disclosure are only used to distinguish different steps, devices, or modules, and neither represent any specific technical meaning nor indicate their inherent logical sequence.

[0038] It should also be understood that in the embodiments of the present disclosure, "a plurality of" can mean two or more, and "at least one" can mean one, two, or more.

[0039] It should also be understood that for any component, data, or structure mentioned in the embodiments of the present disclosure, one or more can be generally understood unless specifically limited or given the opposite implication by the context.

[0040] In addition, the term "and / or" in the present disclosure is merely used to describe an associated relationship between associated objects, and can represent three relationships, for example, A and / or B can represent three cases of A alone, A and B together, and B alone. In addition, the character " / " in the present disclosure generally represents an "or" relationship between the front and rear associated objects.

[0041] It should also be understood that the description of the various embodiments of the present disclosure focuses on the differences between the various embodiments, and the same or similar parts can be referred to each other, and for the sake of brevity, will not be described one by one.

[0042] At the same time, it should be understood that, for the convenience of description, the size of each part shown in the drawings is not drawn according to the actual proportional relationship.

[0043] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present disclosure, its application or uses.

[0044] Techniques and equipment known to those of ordinary skill in the relevant art can not be discussed in detail, but in appropriate cases, the techniques and equipment should be considered as part of the specification.

[0045] It should be noted that similar reference numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0046] Figure 1 is a structural schematic diagram of a direct current calibration pre-stage circuit provided by an exemplary embodiment of the present disclosure. As shown in Figure 1 The direct current calibration pre-stage circuit includes a modulation circuit 2, an alternating current coupling circuit 3, a multiplication circuit 4 and a low-pass filter circuit 5.

[0047] At least two input terminals of the modulation circuit 2 are connected with an output terminal of the signal source 1 and a ground terminal of the signal source 1 respectively, and the modulation circuit 2 is used to alternately receive the effective level signal and the zero point level signal of the signal source 1 based on a first modulation signal, so as to modulate the direct current signal output by the signal source 1 into a first square wave signal. Optionally, the first modulation signal is a square wave pulse signal with a preset duty cycle (for example, 50%), and the modulation circuit 2 alternately receives the effective level signal and the zero point level signal and outputs under the control of the first modulation signal, so that the output signal is modulated into a square wave signal, i.e., the first square wave signal.

[0048] The input end of the AC coupling circuit 3 is connected with the output end of the modulation circuit 2, and the AC coupling circuit 3 is used to remove the DC component in the first square wave signal and output a second square wave signal. The AC coupling circuit 3 can couple the AC signal from one circuit (i.e. the signal source 1 end) to another circuit (i.e. the tester end), while eliminating the DC component. Alternatively, the AC coupling circuit 3 can transmit the AC signal and block the DC signal by using capacitors or transformers and the like.

[0049] The input end of the multiplication circuit 4 is connected with the output end of the AC coupling circuit 3, and the multiplication circuit 4 is used to multiply the second modulation signal and the second square wave signal. Alternatively, the multiplication circuit 4 is essentially an adjustable amplifier circuit with a preset amplitude (e.g. +1 or -1), and the gain variation frequency is controlled by the second modulation signal. The multiplication circuit 4 can be equivalent to multiplying the second square wave signal and the second modulation signal. The second modulation signal can be a square wave signal.

[0050] The input end of the low-pass filter circuit 5 is connected with the output end of the multiplication circuit 4, and the low-pass filter circuit 5 is used to filter the frequency-doubled cosine signal in the output signal of the multiplication circuit 4 and output a target DC signal.

[0051] The product of the second modulation signal and the second square wave signal is equivalent to the sum of the target DC signal and the frequency-doubled cosine signal, and the amplitude of the target DC signal is in a multiple relationship with the amplitude of the DC signal in the effective level signal.

[0052] Alternatively, the second modulation signal is a square wave signal. According to the Fourier transform principle, the second square wave signal and the second modulation signal are equivalent to the sum of the base frequency sine wave and the infinite odd harmonic superposition, and therefore, multiplying the second square wave signal and the second modulation signal can be equivalent to the sum of the product of a series of sine waves obtained by Fourier expansion of the two signals. The product formula of two sine wave signals with the same frequency and phase is as follows:

[0053]

[0054] Where A and B represent the amplitudes of the sine signals, ω represents the frequency, and t is the time variable. According to the above formula, the product of two sine signals is the sum of a DC signal and a cosine signal, and the frequency of the cosine signal is twice the frequency of the original sine signal, and the amplitude of the DC signal is 1 / 2 of the product of the amplitudes of the two sine signals. Therefore, when the amplitude of the second modulation signal is 1, the amplitude of the target DC signal is half of the amplitude of the DC signal in the effective level signal output by the signal source 1, and thus the DC signal in the effective level signal can be restored.

[0055] The low-pass filter circuit 5 can filter out the high-frequency noise signal in the level signal, and thus, after the second modulation signal is multiplied with the second square wave signal by the multiplication circuit 4, the high-frequency part of the product, i.e., the frequency-doubled cosine signal, can be removed by the low-pass filter circuit 5, and a target direct current signal whose amplitude is in a multiple relationship with the amplitude of the direct current signal in the effective level signal is output, so that the direct current signal in the effective level signal can be restored according to the amplitude relationship between the target direct current signal and the direct current signal in the effective level signal, where the amplitude of the target direct current signal is in a multiple relationship with the amplitude of the direct current signal in the effective level signal, and the multiple is half of the amplitude of the second modulation signal.

[0056] Based on the embodiments of the present disclosure, by arranging the modulation circuit, the AC coupling circuit, the multiplication circuit and the low-pass filter circuit in the direct current calibration pre-stage circuit, the output signal of the signal source is modulated into a first square wave signal by the modulation circuit, and then the direct current part in the first square wave signal is removed by the AC coupling circuit to retain the AC part to obtain a second square wave signal, so that after the second square wave signal is multiplied with the second modulation signal by the multiplication circuit, the product obtained can be equivalent to the sum of a series of sine wave products, and then equivalent to the sum of a direct current signal in a multiple relationship with the direct current part in the effective signal of the signal source and a series of frequency-doubled cosine signals, and then the frequency-doubled cosine signals are filtered out by the low-pass filter circuit, so that the direct current signal in the effective signal can be restored, the noise signal is removed, and the noise reduction and calibration processing of the output signal of the signal source are realized.

[0057] In a possible implementation manner, as shown in Figure 2 The modulation circuit 2 is provided with a first single-pole double-throw switch 21, and at least two input ends of the modulation circuit 2 include a first static contact and a second static contact of the first single-pole double-throw switch 21. The first static contact is connected with the output end of the signal source 1, and the second static contact is connected with the ground end of the signal source 1. The moving contact of the first single-pole double-throw switch 21 is connected with the first static contact when the first modulation signal is high, and is connected with the second static contact when the first modulation signal is low. The first modulation signal is used to control the modulation circuit 2 to switch the received effective level and zero level of the signal source 1, so that the output signal of the signal source 1 is modulated into a square wave signal, i.e., a first square wave signal.

[0058] In a possible implementation manner, as shown in Figure 2 The modulation circuit 2 can also be provided with an amplifier 22 (hereinafter referred to as a first amplifier), the input end of the first amplifier 22 is connected with the moving contact of the first single-pole double-throw switch 21, and the output end of the first amplifier 22 is connected with the input end of the AC coupling circuit 3. The first amplifier 22 is used for amplitude adjustment and signal buffering of the received level signal. The first amplifier 22 can be, for example, a differential amplifier, a three-operational-amplifier instrument amplifier or the like, and the type of the first amplifier 22 is not limited in the embodiments of the present disclosure.

[0059] In one possible implementation, the signal frequency of the first modulation signal is outside a preset frequency range, which includes the signal frequency of low-frequency noise and integer multiples thereof. The low-frequency noise includes at least one of 1 / f noise, power frequency noise, and temperature drift noise. Illustratively, 1 / f noise includes the 1 / f noise of an operational amplifier, a resistor, a diode, etc.; power frequency noise includes, for example, 50 / 60Hz power frequency noise; and temperature drift noise is noise caused by fluctuations in ambient temperature. By controlling the signal frequency of the first modulation signal to be outside the preset frequency range—that is, selecting a frequency other than the signal frequency of low-frequency noise and integer multiples thereof—the modulated first square wave signal can be prevented from being submerged in noise.

[0060] In one possible implementation, such as Figure 3 As shown, the AC coupling circuit 3 includes a capacitor 31, which transmits the AC component of the first square wave signal and blocks the DC component. Furthermore, the AC coupling circuit 3 may also include an amplifier 32 (hereinafter referred to as a second amplifier), which can be used to adjust the amplitude of the second square wave signal and for signal buffering.

[0061] In one possible implementation, such as Figure 4 As shown, the multiplication circuit 4 includes a second single-pole double-throw switch 41 and an operational amplifier 42. The moving contact of the second single-pole double-throw switch 41 is connected to the non-inverting input of the operational amplifier 42, and the two stationary contacts of the second single-pole double-throw switch 41 are connected to the ground terminal and the output terminal of the AC coupling circuit 3, respectively. The second single-pole double-throw switch 41 is used to switch the connection relationship between the moving contact and the two stationary contacts based on the second modulation signal, so as to multiply the second modulation signal and the second square wave signal through the operational amplifier.

[0062] In one possible implementation, the first modulation signal and the second modulation signal are square wave signals with the same frequency and phase. When the moving contact of the second single-pole double-throw switch 41 is connected to the stationary contact corresponding to the output terminal of the AC coupling circuit 3, the moving contact of the first single-pole double-throw switch 21 is connected to the stationary contact corresponding to the output terminal of the signal source 1. The second square wave signal is input to the operational amplifier 42 through the non-inverting input terminal "+", and the output signal of the multiplication circuit 4 is the product of the second square wave signal and the signal with the first preset amplitude. Optionally, the signal with the first preset amplitude is a signal with an amplitude of "+1", in which case the output signal of the multiplication circuit 4 is equivalent to the second square wave signal multiplied by 1.

[0063] When the moving contact of the second single-pole double-throw switch 41 is connected with the static contact corresponding to the ground terminal, the moving contact of the first single-pole double-throw switch 21 is connected with the static contact corresponding to the ground terminal of the signal source 1, the second square wave signal is input to the operational amplifier 42 through the inverting input terminal of the operational amplifier 42, and the output signal of the multiplication circuit 4 is the product of the second square wave signal and the signal with the second preset amplitude. The first preset amplitude and the second preset amplitude are opposite numbers. Alternatively, the signal with the second preset amplitude is a signal with an amplitude of "-1", and at this time, the output signal of the multiplication circuit 4 is equivalent to the second square wave signal multiplied by "-1".

[0064] That is, when Figure 5 The gain of the multiplication circuit 4 is 1 when the single-pole double-throw switches of the modulation circuit 2 and the multiplication circuit 4 are switched to the upper side at the same time, and the gain of the multiplication circuit 4 is "-1" when the single-pole double-throw switches of the modulation circuit 2 and the multiplication circuit 4 are switched to the lower side at the same time, thereby realizing the effect of multiplying the second square wave signal by the second modulation signal with a jump of ±1V. Based on the above formula (1), it can be concluded that the amplitude of the target direct current signal in the output signal of the multiplication circuit 4 is 1 / 2 of the amplitude of the direct current signal in the effective signal of the signal source 1, and the direct current part of the effective signal of the signal source 1 can be restored through an amplifier or the like.

[0065] In a possible implementation manner, as shown in Figure 5 The output end of the low-pass filter circuit 5 is connected with an analog-to-digital conversion circuit 6, and the analog-to-digital conversion circuit 6 is configured to encode the received analog signal into a digital signal.

[0066] The above describes the basic principles of the present disclosure in combination with specific embodiments, but it should be pointed out that the advantages, advantages, effects and the like mentioned in the present disclosure are only examples and not limitations, and these advantages, advantages, effects and the like cannot be considered as the must-have of each embodiment of the present disclosure. In addition, the above specific details of the disclosure are only for the purpose of example and for the purpose of understanding, and are not limited to the above specific details for the implementation of the present disclosure.

[0067] Each embodiment in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same, similar or corresponding parts of each embodiment can be mutually referred to. The above describes the basic principles of the present disclosure in combination with specific embodiments, but it should be pointed out that the advantages, advantages, effects and the like mentioned in the present disclosure are only examples and not limitations, and these advantages, advantages, effects and the like cannot be considered as the must-have of each embodiment of the present disclosure. In addition, the above specific details of the disclosure are only for the purpose of example and for the purpose of understanding, and are not limited to the above specific details for the implementation of the present disclosure.

[0068] Various embodiments are described herein with progressive levels of generality. Each of the embodiments described herein can be used alone or in combination with any of the other embodiments described herein.

[0069] The block diagrams of the devices, apparatuses, equipment, systems referred to in the present disclosure are only illustrative examples and are not intended to require or imply that the connections, arrangements, configurations must be as shown in the block diagrams. These devices, apparatuses, equipment, systems can be connected, arranged, configured in any manner as will be appreciated by those skilled in the art. Words such as "including," "containing," "comprising," and the like are to be construed in an inclusive fashion, meaning that "consisting of" is to be read into each of these terms, unless these terms are used in accordance with their usage in a particular context. The terms "or" and "and" as used herein are both inclusive and exclusive in the sense that they mean "and / or" unless the context clearly indicates otherwise. The term "such as" as used herein means "such as, but not limited to."

[0070] The devices and equipment of the present disclosure can be implemented in a number of ways. For example, the devices and equipment of the present disclosure can be implemented via software, hardware, firmware, or any combination of software, hardware, and firmware.

[0071] It is also noted that the devices and equipment of the present disclosure can be implemented with additional components or steps. These additional components or steps, if any, will be readily apparent to one of skill in the art and are deemed to be within the scope of the present disclosure.

[0072] The above description of disclosed aspects is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other aspects without departing from the scope of the present disclosure. Thus, the present disclosure is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0073] The above description has been given for the purpose of illustration and description. Furthermore, this description does not purport to be exhaustive or to limit the embodiments of the disclosure to the precise forms disclosed. Although various example aspects and embodiments have been discussed above, those of ordinary skill in the art will appreciate a variety of modifications, alternatives, permutations, additions, and sub-combinations that fall within the scope of the disclosed aspects.

Claims

1. A direct current calibration pre-stage circuit, characterized by, The modulation circuit, the AC coupling circuit, the multiplication circuit and the low-pass filter circuit are included. At least two input terminals of the modulation circuit are connected with an output terminal of a signal source and a ground terminal of the signal source respectively, and the modulation circuit is configured to alternately receive an active level signal and a zero level signal of the signal source based on a first modulation signal, so as to modulate a direct current signal output by the signal source into a first square wave signal. An input terminal of the AC coupling circuit is connected with an output terminal of the modulation circuit, and the AC coupling circuit is configured to remove a direct current component in the first square wave signal and output a second square wave signal. An input terminal of the multiplication circuit is connected with an output terminal of the AC coupling circuit, and the multiplication circuit is configured to multiply a second modulation signal with the second square wave signal. An input terminal of the low-pass filter circuit is connected with an output terminal of the multiplication circuit, and the low-pass filter circuit is configured to filter a frequency multiplication cosine signal in an output signal of the multiplication circuit and output a target direct current signal. The product of the second modulation signal and the second square wave signal is equivalent to the sum of the target direct current signal and the frequency multiplication cosine signal, and the amplitude of the target direct current signal is in a multiple relationship with the amplitude of a direct current signal in the active level signal.

2. The direct current calibration pre-stage circuit of claim 1, wherein, A first single-pole double-throw switch is arranged in the modulation circuit, and the at least two input terminals of the modulation circuit include a first stationary contact and a second stationary contact of the first single-pole double-throw switch. The first stationary contact is connected with the output terminal of the signal source, and the second stationary contact is connected with the ground terminal of the signal source. A moving contact of the first single-pole double-throw switch is connected with the first stationary contact when the first modulation signal is at a high level, and is connected with the second stationary contact when the first modulation signal is at a low level.

3. The direct current calibration pre-stage circuit of claim 2, wherein, An amplifier is arranged in the modulation circuit, an input terminal of the amplifier is connected with the moving contact of the first single-pole double-throw switch, and an output terminal of the amplifier is connected with an input terminal of the AC coupling circuit. The amplifier is configured to perform amplitude adjustment and signal buffering on a received level signal.

4. A direct current calibration pre-stage circuit according to any one of claims 1 to 3, characterized in that, The signal frequency of the first modulation signal is outside a preset frequency range, the preset frequency range includes a signal frequency of a low-frequency noise and an integer multiple of the signal frequency of the low-frequency noise, and the low-frequency noise includes at least one of 1 / f noise, power frequency noise and temperature drift noise.

5. A direct current calibration pre-stage circuit according to any one of claims 1 to 3, characterized in that A capacitor is arranged in the AC coupling circuit, and the capacitor is configured to transmit an alternating current component in the first square wave signal and block a direct current component in the first square wave signal.

6. A direct current calibration pre-stage circuit according to any one of claims 1 to 3, characterized in that A second single-pole double-throw switch and an operational amplifier are arranged in the multiplication circuit. A moving contact of the second single-pole double-throw switch is connected with a non-inverting input terminal of the operational amplifier, and two stationary contacts of the second single-pole double-throw switch are connected with a ground terminal and an output terminal of the AC coupling circuit respectively. The second single-pole double-throw switch is configured to switch a connection relationship between the moving contact and the two stationary contacts based on the second modulation signal, so as to multiply the second modulation signal with the second square wave signal through the operational amplifier.

7. The direct current calibration pre-stage circuit of claim 6, wherein, The first modulation signal and the second modulation signal are square wave signals with the same frequency and the same phase. When the moving contact of the second single-pole double-throw switch is connected with the fixed contact of the ground terminal, the second square wave signal is input to the operational amplifier through the inverting input terminal of the operational amplifier, and the output signal of the multiplication circuit is the product of the second square wave signal and a signal with a first preset amplitude; When the moving contact of the second single-pole double-throw switch is connected with the fixed contact corresponding to the output terminal of the alternating current coupling circuit, the second square wave signal is input to the operational amplifier through the non-inverting input terminal of the operational amplifier, and the output signal of the multiplication circuit is the product of the second square wave signal and a signal with a second preset amplitude, the first preset amplitude and the second preset amplitude being opposite numbers.

8. A direct current calibration pre-stage circuit according to any one of claims 1 to 3, characterized in that, The output terminal of the low-pass filter circuit is connected with an analog-to-digital conversion circuit, and the analog-to-digital conversion circuit is used for encoding the received analog signal into a digital signal.

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