Plural pole current filter circuit

Abstract

The invention discloses a current filter circuit with a plurality of poles, and relates to the technical field of current filtering, and the current filter circuit with the plurality of poles comprises a first transistor, a second transistor and a plurality of pole filtering modules, the first transistor is used for inputting an initial current signal, the second transistor is used for outputting a filtering current signal, the input end and the output end of the plurality of pole filtering modules are both connected with the first transistor, and the output end of the plurality of pole filtering modules is further connected with the second transistor. Output signals of the plurality of pole filtering modules are fed back to the first transistor and are transmitted to the second transistor; the complex pole filtering module comprises an active device and a passive device, and the active device and the passive device are used for filtering the initial current signal. The current filter has the advantages that the current filter has a higher quality factor and a wider signal bandwidth, and the out-of-band rejection capability of current filtering is improved.

Description

Technical Field

[0001] This application relates to the technical field of current filtering, and particularly to a complex-pole current filtering circuit. Background Art

[0002] In radio frequency and analog systems, noise and interference are the main factors deteriorating system performance. Filter circuits, as the main circuits for anti-noise and anti-interference, are widely used. Filters are generally divided into two categories: voltage-type and current-type. The input and output of voltage-type filters are both voltage quantities, and the input and output of current-type filters are both current quantities.

[0003] In the related art, when a current-type filter processes a signal, due to the non-ideal characteristics of circuit components, the quality factor of the filter is relatively low and the signal bandwidth is relatively narrow. Summary of the Invention

[0004] An object of this application is to at least solve one of the technical problems existing in the prior art, and to provide a complex-pole current filtering circuit, aiming to enable the current filter to have a higher quality factor, a wider signal bandwidth, and improve the out-of-band rejection ability of current filtering.

[0005] In a first aspect, an embodiment of this application provides a complex-pole current filtering circuit, including: a first transistor, a second transistor, and a complex-pole filtering module; The first transistor is used to input an initial current signal, the second transistor is used to output a filtered current signal. Both the input end and the output end of the complex-pole filtering module are connected to the first transistor. The output end of the complex-pole filtering module is further connected to the second transistor. The output signal of the complex-pole filtering module is fed back to the first transistor and transmitted to the second transistor; The complex-pole filtering module includes active devices and passive devices, and the active devices and the passive devices are used to filter the initial current signal.

[0006] According to the technical solution of the embodiment of this application, it has at least the following beneficial effects: The filtering module adopts a complex-pole filtering module. On the premise of having the same out-of-band rejection performance, compared with a real-pole filtering module composed of resistors and capacitors, the complex-pole filtering module has a higher quality factor and a wider signal bandwidth, and can meet more different filtering requirements and achieve a better filtering effect; The complex-pole filtering module includes active devices and passive devices. Compared with a passive filtering module, the complex-pole frequency that the active filtering module can achieve is more flexible, and the circuit structure is also more diverse.

[0007] According to some embodiments of the present application, the drain of the first transistor is used to input an initial current signal. The drain of the first transistor is connected to the input end of the complex pole filtering module. The output end of the complex pole filtering module is connected to the gate of the first transistor. The output end of the complex pole filtering module is also connected to the gate of the second transistor. The drain of the second transistor outputs a filtered current signal.

[0008] According to some embodiments of the present application, the complex pole filtering module is used to filter the initial current signal and then output a filtered voltage signal.

[0009] According to some embodiments of the present application, the filtered voltage signal is simultaneously output to the gate of the first transistor and the gate of the second transistor.

[0010] According to some embodiments of the present application, the filtered voltage signal is fed back to the gate of the first transistor to eliminate the voltage change at the drain of the first transistor caused by the input of the initial current signal.

[0011] According to some embodiments of the present application, when the size of the second transistor is the same as the size of the first transistor, the filtered current signal is the same as the current signal in the first transistor.

[0012] According to some embodiments of the present application, when the size of the second transistor is changed such that the size of the second transistor is different from the size of the first transistor, the magnitude of the filtered current signal changes accordingly.

[0013] According to some embodiments of the present application, both the first transistor and the second transistor are N-type MOS transistors or P-type MOS transistors.

[0014] According to some embodiments of the present application, when the first transistor and the second transistor are P-type MOS transistors, the complex pole current filtering circuit further includes a VDD power supply terminal. The source of the first transistor and the source of the second transistor are connected to the VDD power supply terminal.

[0015] According to some embodiments of the present application, it further includes a passive filtering module. The passive filtering module is connected between the output end of the complex pole filtering module and the second transistor. The passive filtering module is used to filter the output signal of the complex pole filtering module.

[0016] Other features and advantages of the present application will be described in the subsequent specification. And, in part, they will be obvious from the specification, or can be understood by implementing the present application. The objectives and other advantages of the present application can be achieved and obtained through the structures specifically pointed out in the specification, claims, and drawings. Description of the Drawings

[0017] The accompanying drawings are used to provide a further understanding of the technical solutions of the present application, and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solutions of the present application, and do not constitute a limitation to the technical solutions of the present application.

[0018] The present application will be further described below in conjunction with the accompanying drawings and embodiments; Figure 1 is a schematic structural diagram of a complex pole current filtering circuit provided by an embodiment of the present application; Figure 2 is a schematic structural diagram of an all-real pole current filter in the prior art; Figure 3 is an amplitude-frequency response curve graph of a current filter with real poles and complex poles; Figure 4 is an amplitude-frequency response curve graph of a fourth-order all-real pole filter and a fourth-order partial complex pole filter; Figure 5 is a schematic structural diagram of a complex pole current filtering circuit provided by another embodiment of the present application; Figure 6 is a schematic structural diagram of a complex pole current filtering circuit provided by another embodiment of the present application. Detailed implementation manners

[0019] This part will describe in detail the specific embodiments of the present application. The preferred embodiments of the present application are shown in the accompanying drawings. The role of the accompanying drawings is to supplement the description of the text part of the specification, enabling people to intuitively and vividly understand each technical feature and the overall technical solution of the present application. However, it should not be construed as a limitation to the protection scope of the present application.

[0020] In the description of the present application, it should be understood that for the orientation description, such as the orientation or positional relationship indicated by up, down, front, back, left, right, etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

[0021] In the description of the present application, the meaning of several is one or more, the meaning of multiple is more than two, greater than, less than, exceeding, etc. are understood as not including the number itself, and above, below, within, etc. are understood as including the number itself. If there is a description of first and second, it is only for the purpose of distinguishing technical features and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features In the description of the present application, unless otherwise clearly defined, terms such as "setting", "installation", "connection", etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present application in combination with the specific content of the technical solution.

[0022] The following will further elaborate on the present application in conjunction with the attached Figures 1 - 6 .

[0023] As Figure 1 shown, Figure 1 is a schematic diagram of a complex-pole current filtering circuit provided by an embodiment of the present application. The complex-pole current filtering circuit includes: a first transistor M1, a second transistor M2, and a complex-pole filtering module; The first transistor M1 is used to input an initial current signal Iin, the second transistor M2 is used to output a filtered current signal Iout. Both the input terminal and the output terminal of the complex-pole filtering module are connected to the first transistor M1, and the output terminal of the complex-pole filtering module is also connected to the second transistor M2. The output signal of the complex-pole filtering module is fed back to the first transistor M1 and transmitted to the second transistor M2; The complex-pole filtering module includes active devices and passive devices, and the active devices and passive devices are used to filter the initial current signal.

[0024] Referring to Figure 2 , Figure 2 is a full-real-pole current filter. The drain and gate of transistor N0 are both connected to node A1. The initial current signal Ii1 is input from node A1 and converted into a voltage signal at node A1. This voltage signal is transmitted through a filtering network composed of resistor R0, capacitor C0, resistor R1, capacitor C1, resistor R2, capacitor C2, resistor R3, and capacitor C3 and then reaches the gate node of transistor N1. High-frequency signal components are filtered out by the filtering network, and low-frequency signal components are converted into an output current Io1 by the electrical characteristics of transistor N1 and output from the drain of transistor N1; Figure 2 The real-pole filter composed of the shown resistors and capacitors has a low quality factor. On the premise of having the same out-of-band rejection performance, a filter with a low quality factor has a smaller signal bandwidth; Referring to Figure 3 , curve 1 is the amplitude-frequency response curve of a real pole with the same order, curve 2 is the amplitude-frequency response curve of a filter with complex poles, f2 > f1. Curve 1 drops slowly at frequency f1, and the corresponding real-pole filter has a low quality factor and a narrower signal bandwidth; curve 2 drops steeply at frequency f2, and the corresponding complex-pole filter has a high quality factor and a wider signal bandwidth; In addition, referring to Figure 4, the abscissa is the frequency of the initial current signal of the current filter, and the ordinate is the amplitude of the output current signal of the current filter. The solid curve corresponds to the amplitude-frequency response curve of a fourth-order current filter with complex poles, and the dashed curve corresponds to the amplitude-frequency response curve of a fourth-order current filter with all real poles. The 3dB attenuation signal bandwidth of the solid curve is approximately 41.7MHz, and the 3dB attenuation signal bandwidth of the dashed curve is approximately 6.9MHz; Therefore, in summary, the quality factor of the complex pole current filter is significantly higher than that of the all real pole current filter, and the 3dB attenuation signal bandwidth of the complex pole current filter is also significantly higher than that of the all real pole current filter.

[0025] Reference Figure 1 , the complex pole current filtering circuit provided by the embodiment of the present application includes a first transistor M1, a second transistor M2, and a complex pole filtering module. Both the first transistor M1 and the second transistor M2 include two switching pins and a control pin; The first transistor is used to input an initial current signal. The initial current signal Iin is input from the Vi node at one of the switching pins of the first transistor M1. The other switching pin of the first transistor M1 is grounded. The complex pole filtering module is connected between the Vi node and the V1 node, that is, the Vi node at the first transistor M1 is connected to the input end of the complex pole filtering module. The control pin of the first transistor M1 and the output end of the complex pole filtering module are connected to the V1 node. And, the control pin of the second transistor M2 is also connected to the V1 node. Therefore, the output end of the complex pole filtering module is connected to the control pins of both the first transistor M1 and the second transistor M2 at the same time. In addition to being able to be transmitted to the second transistor M2, the output signal of the complex pole filtering module can also be fed back to the first transistor M1, so that the output signal of the complex pole filtering module can control both the first transistor M1 and the second transistor M2 at the same time; In addition, one of the switching pins of the second transistor M2 is grounded, and the filtered current signal Iout is output from the Vd node at the other switching pin of the second transistor M2.

[0026] The complex pole filtering module includes active devices and passive devices. Therefore, the complex pole filtering module is an active filtering module. The complex pole filtering module also includes a power supply for providing necessary electrical energy for the active devices to enable the active devices to work normally. For example, when the active device is a transistor, the power supply can provide an appropriate bias current or voltage for the gate or other control ports of the transistor to ensure that the device is in the correct on or off state; When the active device is an operational amplifier or a circuit module including a power supply, the power supply can provide a working voltage or current for the operational amplifier or other active devices so that they can perform the expected filtering function; In the case of temperature, process, or load changes, the power supply can maintain the operating point of the active device stable and ensure the performance of the circuit; It can be understood that the active and passive devices in the complex pole filter module are used to filter the initial current signal. The active devices can be operational amplifiers, integrated circuits (ICs), bipolar junction transistors (BJTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), etc., and the passive devices can be resistors, capacitors, inductors, etc. Therefore, the circuit structure of the complex pole filter module can be implemented in various ways. The complex pole filter module can be designed according to the filtering requirements, and the corresponding active and passive devices can be selected according to the parameters of the complex pole filter module, such as the order of the filter, the center frequency, the bandwidth, the in-band ripple, the out-of-band rejection, the phase response, etc.; In addition, the complex pole filter module is a second-order or higher-order filter module because only when the system is at least second-order can complex poles occur. Therefore, the complex pole filter module is a multi-order active complex pole filter module, and the multi-order active complex pole filter module can provide a steeper roll-off rate, better selectivity, and possible zero adjustment to change the frequency response of the filter.

[0027] It can be understood that the first transistor M1 and the second transistor M2 can be bipolar junction transistors (BJTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), or insulated gate bipolar transistors (IGBTs), etc. In this embodiment, the first transistor M1 and the second transistor M2 are preferably metal-oxide-semiconductor field-effect transistors (MOSFETs), that is, MOS transistors; It can be foreseen that since the control pins of the first transistor M1 and the second transistor M2 are both connected to the V1 node and a voltage needs to be applied to turn on the first transistor M1 and the second transistor M2, the output signal of the complex pole filter module is a voltage signal. It can be considered that in addition to filtering the initial current signal Iin, the complex pole filter module also converts the initial current signal Iin into a voltage signal; It can be understood that the complex pole filter module can be regarded as a filter transimpedance blocker, that is, a circuit module combining a filter and a transimpedance amplifier. The input current is converted into an output voltage through the transimpedance amplifier, and signals of specific frequencies are allowed to pass through the filter while suppressing signals of other frequencies; Based on this, refer to Figure 1, when the initial current signal Iin is input from the Vi node and enters the complex pole filtering module, the complex pole filtering module filters the initial current signal Iin and converts it into a voltage signal. For example, low-pass filtering, high-pass filtering, band-pass filtering, or band-stop filtering. Subsequently, the output signal of the complex pole filtering module acts on the control pins of the first transistor M1 and the second transistor M2 simultaneously. After receiving the voltage signal output by the complex pole filtering module, the second transistor M2 conducts. At the same time, the first transistor M1 converts the voltage signal into a current signal. At this time, the current signal of the first transistor M1 is the current signal after filtering the initial current signal Iin. And because the second switch pins of both the first transistor M1 and the second transistor M2 are grounded, the voltage differences from the control pins to the second switch pins in the first transistor M1 and the second transistor M2 are equal. Therefore, when the sizes of the first transistor M1 and the second transistor M2 are exactly the same, the mismatch caused by the voltage differences of the first switch pins of the first transistor M1 and the second transistor M2 can be ignored. The first transistor M1 and the second transistor M2 can be regarded as a current mirror structure. The second transistor M2 can copy the current in the first transistor M1 so that the current of the first switch pin of the second transistor M2 is the same as that of the first switch pin of the first transistor M1. Thus, the second transistor M2 copies the current signal after filtering the initial current signal Iin in the first transistor M1 to obtain the filtered current signal Iout in the second transistor M2. The filtered current signal Iout is then output from the first switch pin of the second transistor M2. Thus, the filtering process of the initial current signal Iin is realized; When the sizes of the first transistor M1 and the second transistor M2 are different, since the current flowing through the transistor is related to factors such as the size of the transistor and the gate voltage (control pin voltage), when the control pin voltage remains unchanged, changing the size of the second transistor M2 by N times can make the output current N times the initial current. And in this embodiment, the control pin voltages of the first transistor M1 and the second transistor M2 are the same. Therefore, when the sizes of the first transistor M1 and the second transistor M2 are different, the ratio of the size of the second transistor M2 to the size of the first transistor M1 can be regarded as equal to the ratio of the filtered current signal Iout to the initial current signal Iin.

[0028] In the complex pole current filtering circuit provided in some embodiments of the present application, as Figure 1 shown, the drain of the first transistor is used to input the initial current signal. The drain of the first transistor is connected to the input end of the complex pole filtering module. The output end of the complex pole filtering module is connected to the gate of the first transistor. The output end of the complex pole filtering module is also connected to the gate of the second transistor. The drain of the second transistor outputs the filtered current signal.

[0029] In this embodiment, taking the first transistor M1 and the second transistor M2 as MOS transistors as an example, the initial current signal Iin is input from the Vi node. The source of the first transistor M1 is grounded. The Vi node is connected to the input end of the complex pole filtering module. The gate of the first transistor M1 and the output end of the complex pole filtering module are connected to the V1 node. Moreover, the gate of the second transistor M2 is also connected to the V1 node. The source of the second transistor M2 is grounded. The filtered current signal Iout is output from the drain Vd node of the second transistor M2. Moreover, since the gates of the first transistor M1 and the second transistor M2 are both connected to the V1 node, and the gates of the first transistor M1 and the second transistor M2 are control pins and need to be applied with a voltage to turn on the first transistor M1 and the second transistor M2. Therefore, the output signal of the complex pole filtering module is a voltage signal. It can be considered that in addition to filtering the initial current signal Iin, the complex pole filtering module also converts the initial current signal Iin into a voltage signal. Based on this, referring to Figure 1 , when the initial current signal Iin is input from the Vi node and then enters the complex pole filtering module, the complex pole filtering module filters the initial current signal Iin and converts it into a voltage signal. For example, low-pass filtering, high-pass filtering, band-pass filtering, or band-stop filtering. Subsequently, the output signal of the complex pole filtering module acts on the gates of the first transistor M1 and the second transistor M2 at the same time. After receiving the voltage signal output by the complex pole filtering module, the second transistor M2 turns on. At the same time, after receiving the voltage signal output by the complex pole filtering module, the gate of the first transistor M1 turns on. The first transistor M1 converts the voltage signal into a current signal. At this time, the current signal of the first transistor M1 is the current signal after filtering the initial current signal Iin. And since the sources of the first transistor M1 and the second transistor M2 are both grounded, the gate-source voltage differences of the first transistor M1 and the second transistor M2 are equal. When the sizes of the first transistor M1 and the second transistor M2 are exactly the same, the mismatch caused by the drain voltage difference between the first transistor M1 and the second transistor M2 can be ignored. The first transistor M1 and the second transistor M2 can be regarded as a current mirror structure. The second transistor M2 can copy the current in the first transistor M1 so that the drain current of the second transistor M2 is the same as the drain current of the first transistor M1. Thus, the second transistor M2 copies the current signal after filtering the initial current signal Iin in the first transistor M1 to obtain the filtered current signal Iout in the second transistor M2. The filtered current signal Iout is then output from the drain of the second transistor M2. Thus, the filtering process of the initial current signal Iin is realized.

[0030] In the complex pole current filtering circuit provided in some embodiments of the present application, such as Figure 1As shown, the complex pole filtering module is used to filter the initial current signal and then output a filtered voltage signal.

[0031] It can be understood that since the control pins of the first transistor M1 and the second transistor M2 are both connected to the V1 node and a voltage needs to be applied to turn on the first transistor M1 and the second transistor M2, therefore, the output signal of the complex pole filtering module is a voltage signal. The complex pole filtering module can be used to filter the initial current signal Iin and then convert it into a voltage signal to output a filtered voltage signal, or it can convert the initial current signal Iin into a voltage signal and then perform filtering processing to output a filtered voltage signal. In one embodiment, the complex pole filtering module is a low-pass filter. The initial current signal Iin is input from the Vi node. The AC components contained in the initial current signal Iin flow through the complex pole filtering module, and the high-frequency AC components are filtered out. The low-frequency AC components are converted into an AC voltage signal and then output, acting on the gate V1 node of the first transistor M1 and the second transistor M2. The first transistor M1 converts the voltage signal of the node V1 into a current signal, and the second transistor M2 generates a filtered current signal output according to the current in the first transistor M1. Thus, the initial current signal Iin can be regarded as being divided into three parts. Among them, the first part is the high-frequency AC components, which are filtered out by the complex pole filtering module; the second part is a very small amount of low-frequency components, which are absorbed by the components in the complex pole filtering module; the third part is all the remaining low-frequency components, which are absorbed by the first transistor M1. Thus, high-frequency filtering of the initial current signal Iin is achieved.

[0032] In the complex pole current filtering circuit provided in some embodiments of the present application, the filtered voltage signal is simultaneously output to the gates of the first transistor and the second transistor.

[0033] In this embodiment, the output signal of the complex pole filtering module is a filtered voltage signal. The filtered voltage signal acts on the gate V1 node of the first transistor M1 and the second transistor M2. Through the V1 node, the filtered voltage signal is simultaneously output to the gates of the first transistor and the second transistor, so that the first transistor M1 and the second transistor M2 can be turned on synchronously, thereby realizing precise control of the input current signal. Moreover, the gate voltages of the first transistor M1 and the second transistor M2 are jointly determined by the filtered voltage signal, ensuring that the conduction states of the two transistors are the same, thereby improving the stability and filtering effect of the circuit.

[0034] In the complex pole current filtering circuit provided in some embodiments of the present application, the filtered voltage signal is used to feedback to the gate of the first transistor to eliminate the voltage change at the drain of the first transistor caused by the input of the initial current signal.

[0035] It can be understood that when the initial current signal Iin is input to the drain of the first transistor M1, the filtered voltage signal has not been fed back to the gate of the first transistor M1 yet, and the first transistor M1 is not conducting. Then, the drain voltage of the first transistor M1 will change. When the filtered voltage signal is fed back to the gate of the first transistor M1, the first transistor M1 conducts. Therefore, after the gate of the first transistor M1 receives the filtered voltage signal, it will convert the filtered voltage signal into a current signal, thereby eliminating the voltage change at the drain of the first transistor M1 caused by the input of the initial current signal through the converted current signal. Based on this, the first transistor M1 can automatically adjust to compensate for the voltage deviation caused by the fluctuation or change of the initial current signal Iin, improving the stability of the circuit under various working conditions through the feedback mechanism, and thus improving the performance and reliability of the filtering circuit. In addition, the design of the feedback loop can also reduce the transistor characteristic drift of the first transistor M1 caused by temperature changes or other external factors, further enhancing the anti-interference ability of the circuit.

[0036] In the complex-pole current filtering circuit provided in some embodiments of the present application, when the size of the second transistor is the same as that of the first transistor, the filtered current signal is the same as the current signal in the first transistor M1.

[0037] It can be understood that since the gates of the first transistor M1 and the second transistor M2 are commonly connected to the V1 node, and the sources of the first transistor M1 and the second transistor M2 are both grounded, and the gate and drain of the first transistor M1 are also connected through the complex-pole filtering module. Therefore, when the sizes of the first transistor M1 and the second transistor M2 are exactly the same, the mismatch caused by the drain voltage difference between the first transistor M1 and the second transistor M2 can be ignored. The first transistor M1 and the second transistor M2 can be regarded as a current mirror structure. The first transistor M1 is the reference transistor in the current mirror structure, and the second transistor M2 is the output transistor in the current mirror structure. The output transistor can copy the current in the reference transistor. Therefore, the second transistor M2 can copy the current signal in the first transistor M1 to make the filtered current signal of the second transistor M2 the same as the current signal in the first transistor M1.

[0038] In the complex-pole current filtering circuit provided in some embodiments of the present application, when the size of the second transistor M2 changes such that the size of the second transistor M2 is different from that of the first transistor M1, the magnitude of the filtered current signal Iout changes accordingly.

[0039] It can be understood that since the gates of the first transistor M1 and the second transistor M2 are commonly connected to the V1 node, and the sources of the first transistor M1 and the second transistor M2 are both grounded, and the gate and drain of the first transistor M1 are also connected through a complex pole filtering module. Therefore, when the sizes of the first transistor M1 and the second transistor M2 are exactly the same, the mismatch caused by the drain voltage difference between the first transistor M1 and the second transistor M2 can be ignored, and the first transistor M1 and the second transistor M2 can be regarded as a current mirror structure. When the size of the second transistor M2 changes so that the size of the second transistor M2 is different from that of the first transistor M1, the current mirror structure is damaged, that is, the second transistor M2 cannot mirror the current in the first transistor M1; However, since the current flowing through the transistor is related to factors such as the size of the transistor and the gate voltage, etc. In this embodiment, the voltages of the second transistor M2 and the first transistor M1 remain unchanged. Therefore, the filtered current signal output by the second transistor M2 will also change due to the change in the size of the second transistor M2; and, the size ratio of the second transistor M2 to the first transistor M1 can be regarded as equal to the ratio of the filtered current signal Iout to the initial current signal Iin. Therefore, the change amount of the filtered current signal Iout can be judged according to the change amount of the size of the second transistor M2.

[0040] In the complex pole current filtering circuit provided by some embodiments of the present application, both the first transistor and the second transistor are N-type MOS transistors or P-type MOS transistors.

[0041] It can be understood that the output signal of the complex pole filtering module is fed back to the first transistor M1 and transmitted to the second transistor M2, that is, the output signal of the complex pole filtering module can turn on both the first transistor M1 and the second transistor M2. This can be easily achieved when the first transistor M1 and the second transistor M2 are transistors of the same type, because transistors of the same type usually have similar threshold voltages. However, if the first transistor M1 and the second transistor M2 are transistors of different types, the first transistor M1 and the second transistor M2 may have different conduction degrees under the same gate voltage, resulting in inaccurate current replication; and, N-type MOS transistors usually require a positive gate-source voltage to conduct, while P-type MOS transistors require a negative gate-source voltage. If different types of transistors are used, it will be very difficult to provide the correct bias voltage for both the first transistor M1 and the second transistor M2 at the same time; Based on this, the types of the first transistor and the second transistor need to be the same, that is, both the first transistor and the second transistor are N-type MOS transistors, or both the first transistor and the second transistor are P-type MOS transistors.

[0042] In the complex-pole current filtering circuit provided by some embodiments of the present application, when the first transistor and the second transistor are P-type MOS transistors, the complex-pole current filtering circuit further includes a VDD power supply terminal, and the source electrodes of the first transistor and the second transistor are connected to the VDD power supply terminal.

[0043] Reference Figure 1 and Figure 5 , Figure 1 is a schematic diagram of the first transistor M1 and the second transistor M2 being N-type MOS transistors in the complex-pole current filtering circuit, while Figure 5 is a schematic diagram of the first transistor M1 and the second transistor M2 being P-type MOS transistors in the complex-pole current filtering circuit. By comparing Figure 1 and Figure 5 it can be seen that when the first transistor M1 and the second transistor M2 are N-type MOS transistors, the source electrodes of the first transistor M1 and the second transistor M2 are grounded. Since for N-type MOS transistors, the current flows from the drain to the source, the gate-source junction needs to be forward-biased, which can be achieved by grounding the source electrode. When the first transistor M1 and the second transistor M2 are P-type MOS transistors, the complex-pole current filtering circuit further includes a VDD power supply terminal, and the source electrodes of the first transistor M1 and the second transistor M2 are connected to the VDD power supply terminal. Because in P-type MOS transistors, the current flows from the source to the drain, in order to ensure that the transistor can conduct, the emitter must be at a forward bias voltage higher than the base, which can be achieved through the VDD power supply terminal.

[0044] It can be understood that when the first transistor M1 and the second transistor M2 are P-type MOS transistors, the initial current signal Iin also inputs from the Vi node. The source electrodes of the first transistor M1 and the second transistor M2 are connected to the VDD power supply terminal. The Vi node is connected to the input terminal of the complex-pole filtering module. The gate of the first transistor M1 and the output terminal of the complex-pole filtering module are connected to the V1 node. And, the gate of the second transistor M2 is also connected to the V1 node. The filtered current signal Iout outputs from the drain Vd node of the second transistor M2; And, since the gates of the first transistor M1 and the second transistor M2 are both connected to the V1 node, and the gates of the first transistor M1 and the second transistor M2 are control pins, a voltage needs to be applied to make the first transistor M1 and the second transistor M2 conduct. Therefore, the output signal of the complex-pole filtering module is a voltage signal. It can be considered that in addition to filtering the initial current signal Iin, the complex-pole filtering module also converts the initial current signal Iin into a voltage signal; Based on this, reference Figure 5, when the initial current signal Iin is input from the Vi node and enters the complex pole filtering module, the complex pole filtering module filters the initial current signal Iin and converts it into a voltage signal. For example, low-pass filtering, high-pass filtering, band-pass filtering, or band-stop filtering. Subsequently, the output signal of the complex pole filtering module acts on the gates of the first transistor M1 and the second transistor M2 simultaneously. After receiving the voltage signal output by the complex pole filtering module, the second transistor M2 conducts; at the same time, after receiving the voltage signal output by the complex pole filtering module, the gate of the first transistor M1 conducts, and the first transistor M1 converts the voltage signal into a current signal. At this time, the current signal of the first transistor M1 is the current signal after filtering the initial current signal Iin. And because the sources of the first transistor M1 and the second transistor M2 are both grounded, the gate-source voltage differences of the first transistor M1 and the second transistor M2 are equal. When the sizes of the first transistor M1 and the second transistor M2 are exactly the same, the mismatch caused by the drain voltage difference between the first transistor M1 and the second transistor M2 can be ignored. The first transistor M1 and the second transistor M2 can be regarded as a current mirror structure. The second transistor M2 can copy the current in the first transistor M1 so that the drain current of the second transistor M2 is the same as the drain current of the first transistor M1. Thus, the second transistor M2 copies the current signal after filtering the initial current signal Iin in the first transistor M1 to obtain the filtered current signal Iout in the second transistor M2. The filtered current signal Iout is then output from the drain of the second transistor M2. Thus, the filtering process of the initial current signal Iin is realized.

[0045] In another embodiment, referring to Figure 6 , Figure 6 is a schematic diagram of the first transistor M1 and the second transistor M2 in the complex pole current filtering circuit being N-type MOS transistors. In the figure, the initial current signal Iin is input from the Vi node. The gate of the first transistor M1 is connected to the node V1, the source of the first transistor M1 is grounded, the gate of the second transistor M2 is connected to the node V1, the source of the second transistor M2 is grounded, the drain of the second transistor M2 is connected to the node Vd and serves as the output terminal for the filtered current signal Iout, and the complex pole filtering module is connected between the Vi node and the V1 node; The complex pole filtering module includes the following circuit structure: The source of the third transistor M3 is connected to the Vi node, the gate of the third transistor M3 is connected to the VG node, and the drain of the third transistor M3 is connected to one end of the DC bias current Id1, the negative input terminal of the first active amplifier A1, one end of the first resistor R1, and one end of the first capacitor C1 at the node Vx1. The other end of the DC bias current Id1 is connected to the power supply Vdd. The bias voltage source Vdc1 is connected between the node VG and Gnd. One end of the bias voltage source Vdc2 is connected to the common-mode voltage node VCM, and the other end is grounded. The positive input terminal of the first active amplifier A1 is connected to the common-mode voltage node VCM. The other end of the first resistor R1, the other end of the first capacitor C1, the output terminal of the first active amplifier A1, and one end of the second resistor R2 are connected to the node Vx2. The other end of the second resistor R2, the negative input terminal of the active amplifier A2, and one end of the second capacitor C2 are connected to the node Vx3. The positive input terminal of the second active amplifier A2 is connected to the common-mode voltage node VCM. The other end of the second capacitor C2 and the output terminal of the second active amplifier A2 are connected to the node V1; Figure 6 Among them, the voltage source Vdc1 provides a voltage bias for the gate of the third transistor M3; the voltage source Vdc2 provides a common-mode reference voltage for the first active amplifier A1 and the second active amplifier A2; the bias current Id1 provides a DC bias current for the third transistor M3; The initial current signal Iin flows in from the node Vi. Due to the characteristic that the source of the third transistor M3 has a low AC input impedance, the AC component of Iin flows through the third transistor M3 and enters the Vx1 node; the first-stage low-pass active filter composed of the first resistor R1, the first capacitor C1, and the first active amplifier A1 can suppress the high-frequency components in the initial current signal Iin; the second-stage low-pass active filter composed of the second resistor R2, the second capacitor C2, and the second active amplifier A2 can further suppress the high-frequency components in the output signal of the first-stage low-pass filter; Therefore, almost only the low-frequency components remain in the AC signal reaching the V1 node. These low-frequency AC signals are fed back to the Vi node by the first transistor M1 to eliminate the voltage change at this node caused by the injection of the initial current signal Iin. Finally, the initial current signal Iin is divided into three parts: the first part is the high-frequency AC component, which is filtered out by the active filtering module; the second part is a very small amount of low-frequency components, which are absorbed by the active filtering module; the third part is all the remaining low-frequency components, which are absorbed by the first transistor M1. Since the gate-source voltage difference of the first transistor M1 and the second transistor M2 is equal, assuming that the sizes of the first transistor M1 and the second transistor M2 are exactly the same and ignoring the mismatch caused by the difference in the drain voltages of the first transistor M1 and the second transistor M2, the currents flowing through the first transistor M1 and the second transistor M2 are exactly the same; thus, the high-frequency filtering and mirror output functions of the initial current signal Iin are realized.

[0046] In the complex pole current filtering circuit provided by some embodiments of the present application, a passive filtering module is further included. The passive filtering module is connected between the output end of the complex pole filtering module and the second transistor, and the passive filtering module is used to filter the output signal of the complex pole filtering module.

[0047] In this embodiment, the complex pole current filtering circuit further includes a passive filtering module. The passive filtering module is connected between the output end of the complex pole filtering module and the second transistor. The passive filtering module can be a filtering module composed of a resistor and a capacitor. Thus, before the output signal of the complex pole filtering module is transmitted to the second transistor M2, the passive filtering module filters the output signal of the complex pole filtering module. At this time, the second transistor M2 does not receive all the signals output by the complex pole filtering module, but receives part of the signals output by the complex pole filtering module. Because the passive filtering module can effectively reduce the noise and fluctuations of the output signal of the complex pole filtering module, making the filtered current signal output by the second transistor M2 more stable. And the passive filtering module can reduce the non-linear fluctuations of the gate voltage of the second transistor M2, improve the linearity of the output of the second transistor M2, and reduce the distortion of the current signal output by the second transistor M2.

[0048] The embodiments of the present application have been described in detail above in conjunction with the accompanying drawings. However, the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the purpose of the present application.

Claims

1. A complex pole current filter circuit, characterized in that: include: A first transistor, a second transistor and a complex pole filter module; The first transistor is used to input an initial current signal, the second transistor is used to output a filtered current signal, the input end and the output end of the complex pole filter module are both connected to the first transistor, the output end of the complex pole filter module is also connected to the second transistor, and the output signal of the complex pole filter module is fed back to the first transistor and transmitted to the second transistor; The complex pole filter module includes active devices and passive devices, and the active devices and the passive devices are used to filter the initial current signal.

2. The complex pole current filter circuit according to claim 1, characterized in that: The drain of the first transistor is used to input an initial current signal, the drain of the first transistor is connected to the input end of the complex pole filter module, the output end of the complex pole filter module is connected to the gate of the first transistor, the output end of the complex pole filter module is also connected to the gate of the second transistor, and the drain of the second transistor outputs a filtered current signal.

3. The complex pole current filter circuit according to claim 2, characterized in that: The complex pole filter module is used to filter the initial current signal and then output a filtered voltage signal.

4. The complex pole current filter circuit according to claim 3, characterized in that: The filtered voltage signal is output to the gate of the first transistor and the gate of the second transistor simultaneously.

5. The complex pole current filter circuit according to claim 4, characterized in that: The filtered voltage signal is used to feed back to the gate of the first transistor to eliminate the voltage change of the drain of the first transistor caused by the initial current signal input.

6. The complex pole current filter circuit according to claim 2, characterized in that: When the size of the second transistor is the same as the size of the first transistor, the filtered current signal is the same as the current signal in the first transistor.

7. The complex pole current filter circuit according to claim 5, characterized in that: When the size of the second transistor changes so that the size of the second transistor is different from the size of the first transistor, the size of the filter current signal changes accordingly.

8. The complex pole current filter circuit according to claim 2, characterized in that: The first transistor and the second transistor are both N-type MOS transistors or P-type MOS transistors.

9. The complex pole current filter circuit according to claim 2, characterized in that: When the first transistor and the second transistor are P-type MOS tubes, the complex pole current filter circuit further includes a VDD power supply terminal, and the source of the first transistor and the source of the second transistor are connected to the VDD power supply terminal.

10. The complex pole current filter circuit according to claim 2, characterized in that: It also includes a passive filtering module, which is connected between the output end of the complex pole filtering module and the second transistor, and is used for filtering the output signal of the complex pole filtering module.

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