A low noise baseline restoration circuit

Abstract

The application provides a low-noise baseline recovery circuit, and belongs to the technical field of nuclear electronics. The low-noise baseline recovery circuit comprises a signal input circuit, a pre-amplification circuit, a signal output circuit and a baseline automatic zeroing circuit. The baseline automatic zeroing circuit comprises a direct current component extraction circuit, a buffer circuit and a differential amplification circuit. The signal input circuit is connected to the direct current component extraction circuit through the pre-amplification circuit. The buffer circuit and the pre-amplification circuit are respectively connected to differential input ends of the differential amplification circuit. An output end of the differential amplification circuit is connected to the signal output circuit. The baseline recovery circuit is simple to debug, can achieve the purpose of baseline recovery in actual verification, and has a signal-to-noise ratio superior to that before input. Due to bandwidth limitation, the signal-to-noise ratio is slightly improved, input and output buffers are added, the circuit has certain amplification function, and has strong load capacity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear electronics, and particularly relates to a low-noise baseline recovery circuit and a debugging method thereof. BACKGROUND

[0002] In a nuclear electronics system, in order to amplify and shape the amplitude information of a nuclear detector output pulse signal without distortion, a filter shaping circuit, such as a pole-zero cancellation circuit, a low-pass filter circuit, a baseline recovery circuit, etc., is usually used in a linear circuit after a preamplifier.

[0003] In addition, in nuclear radiation detection, after a detector output signal passes through a signal processing system of a preamplifier, a filter, and a main amplifier, due to the fact that the impulse response of the system often has a slow-decay tail, especially when the count rate is high, the tail accumulation will cause obvious baseline deviation. At the same time, nuclear radiation has a certain amplitude spectrum and is randomly distributed in time, which will also cause the fluctuation of the baseline. In addition, the charging and discharging of the blocking capacitor will also cause the deviation of the baseline, making the spectral line wider, the resolution worse, and the peak position moving. To solve these problems, a baseline recovery circuit needs to be introduced, which is used to overcome the fluctuation of the baseline of the entire electronics system.

[0004] In a nuclear electronics circuit, commonly used baseline restorers include a CD baseline restorer, a CDD baseline restorer, a feedback baseline restorer, a feedforward baseline restorer, etc. The CD baseline recovery circuit uses the nonlinear characteristic of a diode to discharge a capacitor. Although the CD baseline recovery circuit is simple, it will cause the noise to double, which will cause low-energy rays to be unable to be measured for ionizing radiation measuring instruments using weak output signals of sensors. For example, a spectrometer using a SIPM as a sensor hopes to have a high signal-to-noise ratio as much as possible, and the output signal of the SIPM itself is relatively weak. If a traditional baseline recovery circuit is used, the signal-to-noise ratio will at least be reduced by half. The CDD baseline restorer is suitable for bipolar signals, but from the perspective of power consumption, the CDD baseline restorer needs two constant current sources, and the constant current must be maintained when there is no signal, so the power consumption is relatively high, and the constant current sources are not easy to be equal.

[0005] Therefore, some scholars have proposed a feedforward baseline recovery circuit. The circuit directly extracts the DC offset from the input signal through a low-pass filter circuit, and then realizes impedance transformation through a voltage follower in the rear stage, so as to achieve the purpose of baseline recovery by reducing the DC drift of the output signal.

[0006] However, the inventors have found in practical application that in the above scheme, the DC offset is directly extracted from the input signal, which cannot be completed when the input signal is weak. In addition, the DC extraction circuit composed of a simple low-pass filter circuit is not strong in adaptability when the input signal changes, and the direct feed-forward type of amplifier circuit arrangement will bring greater interference to the input signal. More importantly, the above-mentioned feed-forward baseline recovery circuit directly follows the voltage follower in the later stage, and the voltage follower in the later stage will affect the DC component extraction circuit due to the load effect. SUMMARY

[0007] To solve the above technical problems, the present application provides a low-noise baseline recovery circuit and a debugging method thereof.

[0008] In a first aspect of the present application, a low-noise baseline recovery circuit is provided, which comprises a signal input circuit, a pre-amplifier circuit, a signal output circuit and a baseline automatic zero circuit.

[0009] The baseline automatic zero circuit comprises a DC component extraction circuit, a buffer circuit and a differential amplifier circuit.

[0010] The signal input circuit is connected to the DC component extraction circuit through the pre-amplifier circuit.

[0011] The buffer circuit and the pre-amplifier circuit are respectively connected to the differential input terminals of the differential amplifier circuit.

[0012] The output terminal of the differential amplifier circuit is connected to the signal output circuit.

[0013] As one of the advantages of the present application, the pre-amplifier circuit comprises a first differential amplifier, a first resistor and a first capacitor.

[0014] The first resistor and the first capacitor are connected in parallel, one parallel end point is connected to the negative phase input terminal of the first differential amplifier, and the other parallel end point is connected to the output terminal of the first differential amplifier.

[0015] The positive phase input terminal of the first differential amplifier is connected to the signal input circuit.

[0016] Through the pre-amplifier circuit, the problem that the ionizing radiation measuring instrument using a sensor with weak output signal cannot measure low-energy rays is avoided.

[0017] As one of the advantages of the present application, the DC component extraction circuit comprises a second resistor, a second capacitor, a second diode and a second differential amplifier.

[0018] As a further improvement, the second resistor is a variable resistor, and the second capacitor is a variable capacitor.

[0019] The output terminal of the pre-amplifier circuit is connected to the non-inverting input terminal of the second differential amplifier, and is connected to the inverting input terminal of the second differential amplifier through the second resistor;

[0020] The DC component extraction circuit, composed of a second resistor, a second capacitor, a second diode, and a second differential amplifier, can effectively extract the DC component from the input signal after it has been processed by the pre-amplification circuit.

[0021] Furthermore, as a further improvement, the second resistor is a variable resistor and the second capacitor is a variable capacitor, and the resistance and capacitance can be adjusted according to the adaptability.

[0022] The buffer circuit includes a third capacitor, a third resistor, and a third differential amplifier;

[0023] After the third resistor and the third capacitor are connected in parallel, one parallel terminal is connected to the negative input terminal of the third differential amplifier, and the other parallel terminal is connected to the output terminal of the differential amplifier circuit and the third differential amplifier.

[0024] The DC component extraction circuit is connected to the buffer circuit;

[0025] Specifically, the second capacitor and the second resistor of the DC component extraction circuit are connected to the non-inverting input of the third differential amplifier of the buffer circuit.

[0026] The second capacitor is connected to the buffer circuit through the second resistor, and is connected to the output of the second differential amplifier through the second diode.

[0027] As another advantage of the present invention, in the above structure, the buffer circuit composed of the third capacitor, the third resistor and the third differential amplifier is intended to isolate the DC component extraction circuit from the subsequent circuit, so that the subsequent circuit will not affect the DC component extraction circuit due to the load effect.

[0028] Furthermore, the output terminal of the pre-amplifier circuit is connected to the non-inverting input terminal of the fourth differential amplifier through a fifth resistor; the non-inverting input terminal of the fourth differential amplifier is grounded through a sixth resistor.

[0029] Furthermore, the output terminal of the pre-amplifier circuit is connected to the negative input terminal of the second differential amplifier and the positive input terminal of the third differential amplifier through the second resistor.

[0030] In the second aspect of the present application, a debugging method of the low-noise baseline recovery circuit of the first aspect is provided. The debugging method comprises setting the second resistor as a variable resistor and setting the second capacitor as a variable capacitor; and adjusting the response speed of the circuit by changing the values of the second resistor and the second capacitor.

[0031] It has been proved that the traditional CD baseline recovery circuit can double the noise amplitude. Since it is a passive circuit, it has no amplification function and weak load capacity. The improved baseline recovery circuit of the present application is simple to debug. The response speed of the circuit can be adjusted by changing the values of the capacitance and resistance parameters of the baseline zeroing circuit. Actual verification can achieve the purpose of baseline recovery. The signal-to-noise ratio of the output of the circuit is superior to that before input. Since the circuit does not double the noise, but limits the bandwidth to significantly improve the signal-to-noise ratio, and the input and output buffers are added to have certain amplification function and strong load capacity.

[0032] Further advantages of the present application will be further embodied in detail in the specific embodiment part in combination with the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application. Those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0034] Figure 1 is a schematic diagram of a feedforward baseline recovery circuit proposed by the prior art

[0035] Figure 2 is a main module circuit diagram of the low-noise baseline recovery circuit proposed by the present application;

[0036] Figure 3 is Figure 2 the internal structure diagram of the baseline automatic zeroing circuit of the low-noise baseline recovery circuit;

[0037] Figure 4 is Figure 2 the internal structure diagram of the pre-amplification circuit of the low-noise baseline recovery circuit;

[0038] Figure 5 is Figure 2 the internal structure diagram of the direct current component extraction circuit of the low-noise baseline recovery circuit;

[0039] Figure 6 is Figure 2 the internal structure diagram of the buffer circuit of the low-noise baseline recovery circuit;

[0040] Figure 7 is Figure 2 the internal structure diagram of the differential amplifier circuit of the low-noise baseline recovery circuit;

[0041] Figure 8 is Figure 2 the circuit design layout of the low-noise baseline recovery circuit;

[0042] Figure 9 is Figure 2 the circuit parameter layout of the low-noise baseline recovery circuit. DETAILED DESCRIPTION

[0043] The invention will be further described below in conjunction with the drawings and specific embodiments.

[0044] Figure 1 is a schematic diagram of a prior art feedforward baseline recovery circuit proposed in the background art, and the diagram is from the prior art:

[0045] Zhu Haigang. CdZnTe array detection technology research[D]. China Civil Aviation University.

[0046] In this prior art, the author points out that the CD baseline restorer circuit is simple, and since it can only recover single polarity and the baseline level is negative signal; therefore, it is rarely used in practice. The CDD baseline restorer is suitable for bipolar signals, but from the perspective of power consumption, the CDD baseline restorer needs two constant current sources, and must maintain constant current when there is no signal, so the power consumption is relatively high, and the constant current sources are not easy to be equal. The author adopts a feedforward baseline recovery circuit composed of a low-pass filter and a subtraction circuit, which has low static power consumption and simple structure.

[0047] Figure 1 In the prior art, the low-pass filter circuit composed of resistors and capacitors collects the DC offset from the input signal, and the subsequent voltage follower realizes impedance transformation, and together with the operational amplifier constitutes a subtraction circuit, so that the output signal has subtracted the DC offset, thereby achieving the purpose of baseline recovery.

[0048] However, in the above scheme, the DC offset is directly extracted from the input signal, which cannot be extracted when the input signal is weak, especially for spectrometers using SIPM as the sensor, which basically loses its function. For ionizing radiation measuring instruments using sensors with weak output signals, low-energy radiation cannot be measured. For example, a spectrometer using SIPM as a sensor hopes to have as high a signal-to-noise ratio as possible, but the output signal of SIPM itself is relatively weak. If the scheme of using Figure 1 will result in at least a halving of the signal-to-noise ratio.

[0049] In addition, Figure 1The direct current extraction circuit formed by the simple low-pass filter circuit is not strong in adaptability when the input signal changes, and the direct feed-forward type amplification circuit arrangement will bring greater interference to the input signal; more importantly, the above-mentioned feed-forward type baseline recovery circuit directly follows the voltage follower in the latter stage, and the voltage follower in the latter stage will be affected by the load effect on the direct current component extraction circuit.

[0050] To solve the problems of low precision and poor adaptability of the above-mentioned scheme, the inventors have improved and proposed the technical scheme of the present application as follows:

[0051] Referring to Figure 2 , the main module of the low-noise baseline recovery circuit proposed by the present application includes a signal input circuit, a pre-amplification circuit, a signal output circuit and a baseline automatic zeroing circuit.

[0052] Among them, the signal input circuit is connected to the pre-amplification circuit; the baseline automatic zeroing circuit is connected to the signal output circuit.

[0053] Among them, the parameters of the baseline automatic zeroing circuit are adjustable.

[0054] On the basis of Figure 2 , referring to Figure 3 .

[0055] In Figure 3 , it is further shown that the baseline automatic zeroing circuit includes a direct current component extraction circuit, a buffer circuit and a differential amplification circuit.

[0056] In structure, the signal input circuit is connected to the direct current component extraction circuit through the pre-amplification circuit; the direct current component extraction circuit is connected to the buffer circuit;

[0057] The buffer circuit and the pre-amplification circuit are respectively connected to the differential input end of the differential amplification circuit;

[0058] The output end of the differential amplification circuit is connected to the signal output circuit.

[0059] The differential amplification circuit includes a differential amplifier, and the differential amplifier includes a positive phase input end and a negative phase input end.

[0060] The direct current component extraction circuit is connected to the buffer circuit, the output end of the buffer circuit is connected to the negative phase input end of the differential amplification circuit, and the output end of the pre-amplification circuit is connected to the positive phase input end of the differential amplification circuit.

[0061] The parameters of the direct current component extraction circuit are adjustable to adapt to changes.

[0062] On the basis of Figures 2-3 , next Figures 4-7The contents and structures of the pre-amplifier circuit, DC component extraction circuit, buffer circuit, and differential amplifier circuit are shown respectively.

[0063] It is important to note that Figures 4-7 As a separate accompanying drawing, only the respective modules are described in detail; however, those skilled in the art will understand the implications when considering the accompanying drawings. Figures 2-3 The overall structure is understandable. Figures 4-7 There is a relationship between them. Figure 2 Figure 3 The overall connection relationship described above.

[0064] See Figure 4 , Figure 4 yes Figure 2 Internal structure diagram of the pre-amplifier circuit of the low-noise baseline recovery circuit.

[0065] The pre-amplification circuit includes a first differential amplifier, a first resistor, a grounding resistor, and a first capacitor;

[0066] After the first resistor and the first capacitor are connected in parallel, one parallel terminal is connected to the negative input terminal of the first differential amplifier, and the positive input terminal of the first differential amplifier is connected to the signal input circuit. The parallel terminal is grounded through a grounding resistor.

[0067] Another parallel terminal is connected to the output of the first differential amplifier, and this parallel terminal is connected to the DC component extraction circuit and the differential amplifier circuit.

[0068] By using a pre-amplification circuit, the problem of low-energy rays being unmeasurable is avoided, which is caused by using ionizing radiation measuring instruments with weak output signals.

[0069] See next. Figure 5 , Figure 5 yes Figure 2 Internal structure diagram of the DC component extraction circuit of the low-noise baseline recovery circuit.

[0070] The DC component extraction circuit includes a second resistor, a second capacitor, a second diode, and a second differential amplifier;

[0071] The output of the pre-amplifier circuit is directly connected to the non-inverting input of the second differential amplifier, and is connected to the inverting input of the second differential amplifier through the second resistor;

[0072] One end of the second capacitor is connected to the buffer circuit, the second resistor, the second diode and the inverting input of the second differential amplifier, and is connected to the output of the second differential amplifier through the second diode, while the other end is grounded.

[0073] The direct current component extraction circuit composed of the second resistance, the second capacitor, the second diode and the second differential amplifier can effectively extract the direct current component in the input signal processed by the pre-amplification circuit.

[0074] Preferably, the second resistance is a variable resistance, and the second capacitor is a variable capacitor, so that the resistance and the capacitor can be adjusted according to the adaptation.

[0075] Next, referring to Figure 6 , Figure 6 is Figure 2 the internal structure diagram of the buffer circuit of the low-noise baseline recovery circuit.

[0076] In Figure 6 , the buffer circuit comprises a third capacitor, a third resistance and a third differential amplifier.

[0077] The third resistance and the third capacitor are connected in parallel, one parallel end point is connected to the negative phase input end of the third differential amplifier, and the other parallel end point is connected to the output end of the differential amplification circuit and the third differential amplifier.

[0078] As described above, the direct current component extraction circuit is connected to the buffer circuit.

[0079] Specifically, the second capacitor and the second resistance of the direct current component extraction circuit are connected to the positive phase input end of the third differential amplifier of the buffer circuit.

[0080] In the above structure, the buffer circuit composed of the third capacitor, the third resistance and the third differential amplifier is used to isolate the direct current component extraction circuit from the subsequent circuit, so that the subsequent circuit will not affect the direct current component extraction circuit due to the load effect.

[0081] Next, referring to Figure 7 . Figure 7 is Figure 2 the internal structure diagram of the differential amplification circuit of the low-noise baseline recovery circuit.

[0082] In Figure 7 , the differential amplification circuit comprises a fourth capacitor, a fourth resistance and a fourth differential amplifier; the fourth resistance and the fourth capacitor are connected in parallel, one parallel end point is connected to the negative phase input end of the fourth differential amplifier, and the parallel end point is connected to the output end of the buffer circuit through an input differential resistance, i.e., connected to the output end of the third differential amplifier of the buffer circuit.

[0083] The other parallel end point is connected to the signal output circuit and the output end of the fourth differential amplifier.

[0084] Meanwhile, on the basis of Figure 4 , continue to refer toFigure 7 The output end of the pre-amplification circuit is connected to the non-inverting input end of the fourth differential amplifier through a fifth resistor; and the non-inverting input end of the fourth differential amplifier is grounded through a sixth resistor.

[0085] Through the differential amplification circuit, the direct current component separated from the signal output from the pre-amplification circuit and the direct current component are subtracted, so that the baseline of the signal is restored to the zero level position.

[0086] In combination Figures 2-7 , in the above structure, the output end of the first differential amplifier of the pre-amplification circuit is connected to the non-inverting input end of the second differential amplifier of the direct current component extraction circuit and the non-inverting input end of the third differential amplifier of the buffer circuit through the second resistor.

[0087] As a specific embodiment, the pre-amplification circuit, the buffer circuit and the differential amplification circuit adopt a voltage feedback type differential amplifier; and the direct current component extraction circuit adopts a low input bias current operational amplifier.

[0088] Based on Figures 2-7 , Figure 8 is Figure 1 The circuit design layout of the low-noise baseline restoration circuit.

[0089] The design layout is designed by using the circuit layout tool known in the art, and the background grid (shadow grid) represents the layout version, and the remaining component symbols follow the conventional expressions in the art.

[0090] For the convenience of understanding, Figure 7 part of the circuit structure is framed with a rectangular frame, and the actual circuit layout does not have the frame, wherein the pre-amplification circuit frame, the baseline automatic zeroing circuit frame (including the buffer circuit frame, the direct current component extraction circuit frame and the differential amplification circuit frame) are shown.

[0091] For the signal input circuit, SIG_IN is used, and for the signal output circuit, SIG_OUT is used.

[0092] Based on Figure 8 , Figure 9 The specific parameter values of some components in the design layout are given. It can be understood that in the case where the parameter values of some components are not given, the person skilled in the art can reasonably set them according to the actual situation.

[0093] As an illustration, in the Figure 9 parameter values, GND represents ground;

[0094] In one specific embodiment, the pre-amplification circuit, the buffer circuit and the differential amplifier circuit adopt a voltage feedback type differential amplifier; and the DC component extraction circuit adopts a low input bias current operational amplifier.

[0095] The first capacitor is 510 pF, the first resistor is 2K, and the first differential amplifier adopts AD8038AKSZ; the input resistor of the signal input resistor adopts 1K;

[0096] The second resistor adjustment value is 10K, the second capacitor adjustment value is 10uF, and the second diode adopts SDMK0340L-7-F; the second differential amplifier adopts AD8605ARTZ;

[0097] The third capacitor is 1nF, and the third resistor is 10K; the third differential amplifier adopts AD8038AKSZ;

[0098] The fourth capacitor is 200 pF, the fourth resistor is 2K, the input differential resistor is 1K, the fifth resistor is 1K, and the sixth resistor is 2K; the fourth differential amplifier adopts AD8038AKSZ.

[0099] Figure 9 The first to fourth differential amplifiers are also connected with reference voltage ends, which are respectively marked as VCC1-VEE1, VC3V3-GND, VC3V3-VE3V3 and VC5-VE5, and are only identification of the drawings; and the specific reference voltage values can be determined based on the specific model of the differential amplifier.

[0100] Based on the design layout of Figure 8 , the low-noise baseline recovery circuit can be debugged accordingly to meet the actual situation.

[0101] Specifically, the debugging method comprises: setting the second resistor as a variable resistor and setting the second capacitor as a variable capacitor; and the response speed of the circuit can be adjusted by changing the values of the second resistor and the second capacitor.

[0102] It has been proved that the traditional CD baseline recovery circuit can double the noise amplitude, and since it is a passive circuit, it has no amplification function and weak load capacity. The improved baseline recovery circuit has simple debugging, and the response speed of the circuit can be adjusted by changing the values of the capacitance and resistance parameters of the baseline zero circuit. Actual verification can achieve the purpose of baseline recovery, and the signal-to-noise ratio of the circuit output is better than that before input, because the circuit not only does not double the noise, but also significantly improves the signal-to-noise ratio due to bandwidth limitation, and the input and output buffers are added to make the circuit have certain amplification function and strong load capacity.

[0103] While the preferred embodiments of the application have been described, additional variations and modifications can be made to these embodiments by those skilled in the art once they have the benefit of the present disclosure without departing from the spirit and scope of the application. Accordingly, it is intended that the appended claims include all such modifications and variations as fall within the scope of the present application.

[0104] It is apparent that those skilled in the art can make various changes and modifications to the application without departing from the spirit and scope of the application. It is therefore intended that the present application cover all such changes and modifications that are within its scope.

Claims

1. A low-noise baseline recovery circuit comprising a signal input circuit, a pre-amplification circuit, a signal output circuit and a baseline automatic zeroing circuit; characterized in that: the pre-amplification circuit comprises a first differential amplifier, a first resistor and a first capacitor; the first resistor and the first capacitor are connected in parallel, one parallel end point is connected to the negative phase input end of the first differential amplifier, and the other parallel end point is connected to the output end of the first differential amplifier; the positive phase input end of the first differential amplifier is connected to the signal input circuit; the baseline automatic zeroing circuit comprises a direct current component extraction circuit, a buffer circuit and a differential amplification circuit; the signal input circuit is connected to the direct current component extraction circuit through the pre-amplification circuit; the direct current component extraction circuit comprises a second resistor, a second capacitor, a second diode and a second differential amplifier; one end of the second capacitor is connected to the buffer circuit, the second resistor, the second diode and the inverting input end of the second differential amplifier, and the other end is grounded through the second diode; the output end of the pre-amplification circuit is connected to the non-inverting input end of the second differential amplifier and the inverting input end of the second differential amplifier through the second resistor; the buffer circuit and the pre-amplification circuit are respectively connected to the differential input ends of the differential amplification circuit; and the output end of the differential amplification circuit is connected to the signal output circuit.

2. The low-noise baseline recovery circuit according to claim 1, characterized in that: the output end of the buffer circuit is connected to the negative phase input end of the differential amplification circuit.

3. The low-noise baseline recovery circuit according to claim 1, characterized in that: the output end of the pre-amplification circuit is connected to the non-inverting input end of the differential amplification circuit.

4. The low-noise baseline recovery circuit according to claim 1, characterized in that: the buffer circuit comprises a third capacitor, a third resistor and a third differential amplifier; the third resistor and the third capacitor are connected in parallel, one parallel end point is connected to the negative phase input end of the third differential amplifier, and the other parallel end point is connected to the differential amplification circuit.

5. The low-noise baseline recovery circuit according to claim 1, characterized in that: the differential amplification circuit comprises a fourth capacitor, a fourth resistor and a fourth differential amplifier; the fourth resistor and the fourth capacitor are connected in parallel, one parallel end point is connected to the negative phase input end of the fourth differential amplifier, and the other parallel end point is connected to the signal output circuit.

6. The low-noise baseline recovery circuit according to claim 5, characterized in that: the output end of the pre-amplification circuit is connected to the non-inverting input end of the fourth differential amplifier through a fifth resistor; and the non-inverting input end of the fourth differential amplifier is grounded through a sixth resistor.

7. The low-noise baseline recovery circuit according to claim 4, characterized in that: the output end of the pre-amplification circuit is connected to the negative phase input end of the second differential amplifier and the non-inverting input end of the third differential amplifier through the second resistor. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 8. The low noise baseline restoration circuit of claim 1, wherein: the pre-amplification circuit, the buffer circuit and the differential amplification circuit employ a voltage feedback type differential amplifier; and the DC component extraction circuit employs a low input bias current operational amplifier. ​

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