Filter circuit

Abstract

Embodiments of the present disclosure provide a filter circuit, comprising: at least one current mirror configured to mirror and replicate a current, wherein the at least one current mirror includes a first current mirror, the first current mirror comprises a first transistor and a second transistor, and the second transistor is configured to mirror and replicate an input current signal received by the first transistor; a first capacitor connected between a control end and an output end of the second transistor; an active inductor connected to the output end of the second transistor; a voltage conversion module configured to convert the mirrored and replicated current of one of the current mirrors into a voltage signal; and a voltage output end configured to output the converted voltage signal.

Description

A filter circuit

[0001] Cross-reference to related applications

[0002] This disclosure is based on and claims priority to Chinese Patent Application No. 202411194986.0, filed on August 28, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of integrated circuits, and more particularly to a filter circuit. Background Technology

[0004] In integrated circuit design, low-pass current filtering is frequently required, such as for noise reduction and ripple reduction. Currently, the most common low-pass filter is the RC low-pass filter, where RC represents resistor and capacitor. This filter has a simple structure and principle, and its filtering effect is significant, hence its widespread application.

[0005] However, with the continuous advancement of electronic technology, higher requirements have been placed on low-pass filters in order to achieve better low-pass filtering effects.

[0006] Application content

[0007] In view of this, the present disclosure provides a filtering circuit.

[0008] To achieve the above objectives, this disclosure provides a filtering circuit, comprising: at least one current mirror for mirroring and replicating current; the at least one current mirror includes a first current mirror, the first current mirror including a first transistor and a second transistor, the second transistor being used to mirror and replicate an input current signal received by the first transistor; a first capacitor connected between a control terminal and an output terminal of the second transistor; an active inductor connected to the output terminal of the second transistor; a voltage conversion module for converting the mirrored current of one of the current mirrors into a voltage signal; and a voltage output terminal for outputting the converted voltage signal.

[0009] In some embodiments, the active inductor includes a first resistor and a third transistor, wherein the first resistor is located between the control terminal and the input terminal of the third transistor, and the input terminal of the third transistor is connected to the output terminal of the second transistor.

[0010] In some embodiments, the voltage conversion module is used to convert the mirrored current of the first current mirror into the voltage signal, and the voltage conversion module is connected to the output terminal of the second transistor; the voltage output terminal is connected to the output terminal of the second transistor.

[0011] In some embodiments, the at least one current mirror further includes a second current mirror: the second current mirror includes a first transistor and a fourth transistor, the fourth transistor being used to mirror the input current signal received by the first transistor.

[0012] In some embodiments, the voltage conversion module is used to convert the mirrored current of the second current mirror into the voltage signal, and the voltage conversion module is connected to the output terminal of the fourth transistor; the voltage output terminal is connected to the output terminal of the fourth transistor.

[0013] In some embodiments, it further includes: at least one filtering unit, wherein the control terminal of the first transistor, the control terminal of the second transistor of the first current mirror, the filtering unit and the control terminal of the fourth transistor are connected in sequence.

[0014] In some embodiments, a second resistor connected in series with the active inductor is further included, the resistance of the second resistor being greater than the resistance of the voltage conversion module.

[0015] In some embodiments, the voltage conversion module includes a resistor or a transimpedance amplifier.

[0016] In some embodiments, the first transistor and the second transistor include MOS transistors or BJT transistors.

[0017] In some embodiments, the size of the first transistor is smaller than the size of the second transistor.

[0018] In some embodiments, the filter circuit further includes a second capacitor, wherein a first terminal of the second capacitor is connected to the control terminal and the output terminal of the first transistor, and a second terminal of the second capacitor is grounded.

[0019] In some embodiments, the capacitance of the second capacitor is less than the capacitance of the first capacitor.

[0020] In some embodiments, the first current mirror includes a base current mirror, a common-source cascode current mirror, or a self-biased cascaded current mirror.

[0021] This disclosure provides a filtering circuit, comprising: at least one current mirror for mirroring a current; the at least one current mirror includes a first current mirror, the first current mirror including a first transistor and a second transistor, the second transistor being used to mirror an input current signal received by the first transistor; a first capacitor connected between the control terminal and the output terminal of the second transistor; an active inductor connected to the output terminal of the second transistor; a voltage conversion module for converting the mirrored current of one of the current mirrors into a voltage signal; and a voltage output terminal for outputting the converted voltage signal. The first capacitor is located between the control terminal and the output terminal of the second transistor, and the second transistor has an amplification function, allowing a larger amplification value to be obtained using a smaller first capacitor. Because the inflection point frequency of the filtering circuit is related to the capacitance value, a lower inflection point frequency can be obtained, reducing low-frequency ripple in the current to minimize the swing at the input point and saving chip area.

[0022] The active inductor is connected to the output terminal of the second transistor. On the one hand, it expands the bandwidth of the second transistor, enabling the amplification effect of the second transistor to cover higher frequencies. On the other hand, it can also increase the total equivalent impedance of the branch where the second transistor is located within a frequency band, thereby increasing the gain of this frequency band and increasing the amplification factor of the first capacitor. This is beneficial for obtaining a lower inflection point frequency and reducing the swing caused by low-frequency ripple in the current at the current input point.

[0023] Meanwhile, in the filter circuit of this embodiment, since the current signal is input from the first transistor, the input impedance of the filter circuit is related to the transconductance of the first transistor. When the low-frequency input current signal increases, the input impedance of the filter circuit will decrease accordingly. Thus, compared with the traditional RC filter circuit, this embodiment can significantly reduce the voltage swing of the current input node of the filter circuit, so that the current input node can obtain more voltage design margin.

[0024] In addition, in this embodiment of the filter circuit, the active inductor does not provide the function of current-to-voltage conversion, but the current-to-voltage conversion function is implemented by the voltage conversion module. This achieves the separation of low-pass filtering and current-to-voltage conversion, thereby allowing for flexible setting of the voltage signal output from the voltage output terminal and improving the flexibility of circuit design. Attached Figure Description

[0025] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments according to this disclosure and should not be construed as limiting the scope of this disclosure.

[0026] Figure 1A is a circuit diagram of a low-pass filter circuit provided in an example;

[0027] Figure 1B is a schematic frequency response diagram of a low-pass filter;

[0028] Figure 2 is a circuit diagram of a first type of filter circuit provided in an embodiment of this disclosure;

[0029] Figure 3 is a circuit diagram of a second type of filter circuit provided in an embodiment of this disclosure;

[0030] Figure 4 is a circuit diagram of the third type of filter circuit provided in the embodiments of this disclosure;

[0031] Figure 5 is a circuit diagram of the fourth type of filter circuit provided in the embodiments of this disclosure;

[0032] Figure 6 is a schematic diagram of a first type of first current mirror provided in an embodiment of this disclosure;

[0033] Figure 7 is a schematic diagram of a second type of first current mirror provided in an embodiment of this disclosure;

[0034] Figure 8 is a schematic diagram of the third type of first current mirror provided in the embodiments of this disclosure. Detailed Implementation

[0035] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0036] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this disclosure. However, it will be apparent to those skilled in the art that this disclosure may be practiced without one or more of these details. In other instances, to avoid confusion with this disclosure, certain technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and structures described in detail.

[0037] In the accompanying drawings, for clarity, the dimensions of layers, areas, and elements, as well as their relative dimensions, may be exaggerated. The same reference numerals denote the same elements throughout.

[0038] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this disclosure, the first element, component, area, layer, or portion discussed below may be referred to as a second element, component, area, layer, or portion. And the discussion of a second element, component, area, layer, or portion does not imply that the first element, component, area, layer, or portion necessarily exists in this disclosure.

[0039] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below,” “under,” or “below” other elements or features will be oriented “above” other elements or features. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0040] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprise” and / or “comprising,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0041] To fully understand this disclosure, detailed steps and structures will be presented in the following description to illustrate the technical solutions of this disclosure. Preferred embodiments of this disclosure are described in detail below; however, other embodiments may also be implemented in addition to these detailed descriptions.

[0042] In integrated circuit design, low-pass current filtering is frequently required, such as for noise reduction and ripple reduction. Currently, the most common low-pass filter is the RC low-pass filter.

[0043] Referring to Figure 1A, which is a circuit diagram of a low-pass filter circuit provided in an example.

[0044] As shown in Figure 1A, the low-pass filter circuit 100 includes a capacitor C and a resistor R. The capacitor C has a first terminal 101 and a second terminal 102, and the resistor R has a first terminal 103 and a second terminal 104. The first terminal 101 of the capacitor C is connected to the first terminal 103 of the resistor R, and the second terminal 102 of the capacitor C is connected to the second terminal 104 of the resistor R. A working voltage V is connected between the first terminal 101 of the capacitor C and the first terminal 103 of the resistor R. DD A current input terminal 105 and a voltage output terminal 106 are provided between the second terminal 102 of capacitor C and the second terminal 104 of resistor R. The current input terminal 105 is used to input current I. IN The voltage output terminal 106 is used to output voltage V. OUT .

[0045] In Figure 1A, the overall impedance of the low-pass filter circuit 100 is as follows. Here, the capacitance value of capacitor C can be expressed as C, and the resistance value of resistor R can be expressed as R.

[0046] Referring to Figure 1B, which is a schematic frequency response diagram of a low-pass filter.

[0047] As shown in Figure 1B, the low-pass filter circuit 100 has a cutoff frequency, also known as the -3dB cut-off frequency. When the frequency of the input signal is greater than the cut-off frequency, the overall impedance of the low-pass filter circuit 100 will decrease by 20dB for every tenth harmonic. The cut-off frequency of the filter refers to the frequency point at which the filter's frequency response curve begins to deviate significantly from its passband characteristics. At this frequency point, the signal amplitude typically drops to approximately 70.7% of the passband amplitude (i.e., -3dB). For example, in Figure 1B, the horizontal axis represents frequency (in Hz), and the vertical axis represents gain (in dB). Point A corresponds to the cut-off frequency, which is approximately 1kHz.

[0048] For this low-pass filter circuit 100, the output voltage is related to the input current and the overall impedance of the low-pass filter circuit, that is: VOUT =Z IN ×I IN

[0049] From the above formula, we can see that the output voltage V OUT It has the overall impedance Z of the low-pass filter circuit 100 IN With the same frequency response, low-pass filtering can be achieved.

[0050] However, with the continuous advancement of electronic technology, higher requirements are being placed on low-pass filters to achieve better low-pass filtering effects. For example, reducing the 3dB inflection point is necessary to filter out more high-frequency signals while retaining low-frequency signals.

[0051] In some embodiments, the -3dB inflection point can be reduced by increasing the resistor R, causing the -3dB inflection point to shift to the left in the frequency response graph. However, while directly increasing the resistor R can lower the inflection point frequency, the increased impedance before the inflection point frequency will lead to an increase in the input current I. IN The low-frequency ripple in the middle is converted into a larger amplitude output voltage V. OUT Ripple. Therefore, if the low-pass filter circuit is connected to certain critical nodes, such as the amplifier output load, the resistance value of the low-pass filter circuit may be limited. In this case, increasing the resistance R may affect the circuit's quiescent operating point or limit the amplifier's linearity. Here, the quiescent operating point refers to the point on the transistor characteristic curve where the amplifier circuit operates in DC mode when the AC input signal is 0.

[0052] Based on this, the present disclosure provides a filtering circuit.

[0053] Referring to Figure 2, which is a circuit diagram of a first type of filter circuit provided in an embodiment of this disclosure.

[0054] As shown in Figure 2, this embodiment of the present disclosure provides a filter circuit 200, including: at least one current mirror, a first capacitor C1, an active inductor 203, a voltage conversion module 206, and a voltage output terminal 214. In this embodiment, the filter circuit 200 including a first current mirror 202 is described as an example. The first current mirror 202 includes a first transistor M1 and a second transistor M2. The second transistor M2 is used to mirror the input current signal received by the first transistor M1. The first capacitor C1 is connected between the control terminal 204 and the output terminal 205 of the second transistor M2. The active inductor 203 is connected to the output terminal 205 of the second transistor M2. The voltage conversion module 206 is used to convert the mirrored current of one of the current mirrors into a voltage signal V. OUTIn this embodiment, the mirrored current of the first current mirror 202 is used to convert the mirrored current into a voltage signal V. OUT Taking an example, the voltage output terminal 214 is used to output the voltage signal V. OUT .

[0055] Among them, the current signal I IN The ripples in the current are carried away by the first capacitor C1, so there are no ripples in the current flowing into the first transistor M1. In other words, the current flowing into the first transistor M1 is filtered, and the filtered current is replicated by the second transistor M2. Therefore, the replicated current flowing out from the output terminal 205 of the second transistor M2 also has no ripples.

[0056] The branch 207 containing the second transistor M2 can be regarded as a common-source amplifier. The first capacitor C1 is located between the control terminal 204 and the output terminal 205 of the second transistor M2. The capacitance value of the first capacitor C1 can be amplified, so that the filter circuit 200 can obtain a larger amplification value by using the first capacitor C1 with a smaller capacitance value (or smaller area). The larger capacitance value can reduce the inflection point frequency. Therefore, this scheme can obtain a lower inflection point frequency and reduce the low-frequency ripple in the current so that the swing caused at the current input point is smaller, saving chip area.

[0057] The active inductor 203 is connected to the output terminal of the second transistor M2, which can improve the gain of the second transistor M2. The active inductor 203 can expand the bandwidth of the second transistor M2, thereby obtaining a larger amplification value for the first capacitor C1, which can cover higher frequencies. At the same time, the active inductor itself has impedance characteristics, which can increase the total equivalent impedance, thereby increasing the gain of the second transistor M2, further amplifying the capacitance value, and reducing the inflection point frequency.

[0058] The active inductor 203 does not provide the current-to-voltage function, but the voltage conversion module 206 implements the current-to-voltage function, realizing the separation of low-pass filtering and current-to-voltage conversion, thereby flexibly setting the magnitude of the voltage signal output at the voltage output terminal and improving the flexibility of circuit design.

[0059] Because the current signal I IN Since the input is from the first transistor M1, the input impedance of the filter circuit is related to the transconductance of the first transistor M1. When the low-frequency input current signal increases, the input impedance of the filter circuit will decrease accordingly. Thus, compared with the traditional RC filter circuit, the embodiments of this disclosure can significantly reduce the voltage swing of the current input node of the filter circuit, so that the current input node can obtain more voltage design margin.

[0060] Branch 207 can be understood as the branch where the mirrored current of the second transistor M2 in the first current mirror is output. In this embodiment, the voltage conversion module 206 is connected to the output terminal of the second transistor M2 in the first current mirror and is used to convert the mirrored current of the first current mirror into a voltage signal V. OUT The voltage output terminal 214 is connected to the output terminal of the second transistor M2 in the first current mirror, and is used to output the voltage signal V. OUT Therefore, branch 207 includes a second transistor M2, a first capacitor C1 connected between the control terminal 204 and the output terminal 205 of the second transistor M2, and an active inductor 203 and a voltage conversion module 206 connected to the output terminal 205 of the second transistor M2. Here, the active inductor 203 and the voltage conversion module 206 can serve as the load of a common-source amplifier. The control terminal 204 of the second transistor M2 is the input terminal of the common-source amplifier, and the output terminal 205 of the second transistor M2 is the output terminal of the common-source amplifier. The first capacitor C1 connected between the control terminal 204 and the output terminal 205 of the second transistor M2 can be amplified by branch 207 containing the second transistor M2, and the capacitance value of the amplified capacitor can be equivalent to the input terminal of branch 207 containing the second transistor M2. That is, the control terminal 204 of the second transistor M2 is amplified by 1+A. V times, of which A V This is the voltage gain of branch 207 where the second transistor M2 is located.

[0061] As shown in Figure 2, in this embodiment of the present disclosure, in order to further improve the gain of the branch 207 where the second transistor M2 is located and avoid voltage signal V OUT The magnitude of the voltage signal V has a certain impact on the branch 207 where the second transistor M2 is located, to avoid the voltage signal V OUT When the voltage is too high, the second transistor M2 cannot maintain normal operation in the saturation region, thus increasing the active inductor 203. The active inductor 203 may include a first resistor R1 and a third transistor M3. The first resistor R1 is connected between the control terminal 208 (e.g., the gate of the third transistor M3) and the input terminal 209 (e.g., the drain of the third transistor M3). The input terminal 209 of the third transistor M3 is connected to the output terminal 205 of the second transistor M2.

[0062] In this embodiment of the disclosure, if the control terminal 208 and the input terminal 209 of the third transistor M3 are directly connected, the resistance of the active inductor 203 is 1 / g. m3 That is, small resistance, g m3This refers to the transconductance of the third transistor M3. Here, because a first resistor R1 is added between the control terminal 208 and the input terminal 209 of the third transistor M3, the RC time constant of the control terminal 208 of the third transistor M3 increases. When the voltage at the input terminal 209 of the third transistor M3 changes rapidly, the response time of the voltage at the control terminal 208 of the third transistor M3 becomes longer. This results in a very small change in the voltage at the control terminal 208 of the third transistor M3 within a short period of time. Thus, it can be considered that it is connected to an approximately fixed level, making the third transistor M3 exhibit high impedance to high-frequency signals.

[0063] In this embodiment, the first resistor R1 is connected externally to the first current mirror 202, allowing the first capacitor C1 to be amplified at the control terminals of the first transistor M1 and the second transistor M2. For example, when the capacitance of the first capacitor C1 is C, the amplified capacitance after being amplified at the control terminals of the first transistor M1 and the second transistor M2 is (1+A). V C.

[0064] In this embodiment, both the active inductor 203 and the voltage conversion module 206 are connected to the branch 207 where the second transistor M2 is located. The voltage conversion module 206 is connected to the output terminal of the active inductor 203, and the voltage output terminal 214 is also connected to the output terminal of the active inductor 203. Here, the output terminal of the active inductor 203 can be the output terminal of the third transistor M3. Thus, the active inductor 203 of the filter circuit 200 does not provide a current-to-voltage conversion function, thereby separating the low-pass filtering and current-to-voltage conversion processes and improving the flexibility of circuit design.

[0065] In this embodiment, the structure of the first current mirror is illustrated using the structure of a basic current mirror as a reference. That is, the first current mirror includes a first transistor M1 and a second transistor M2, and the input current signal I... IN The image is mirrored to the output terminal 205 of the second transistor M2 at a certain ratio, where the replication ratio can be 1:N, and N can be greater than 1 or less than 1.

[0066] In this embodiment of the disclosure, the voltage conversion module 206 includes a resistor or a transimpedance amplifier. For example, the voltage conversion module 206 includes a resistor R. L The voltage output terminal 214 is connected to the active inductor 203 and the resistor R. L between.

[0067] Referring to Figure 2, the load of branch 207 where the second transistor M2 is located is resistor R. L It is connected in series with the third transistor M3. The resistor R... L One end is connected to the voltage output terminal 214, which can output a voltage signal V. OUTresistance R L The other end is grounded. The amplification factor of branch 207, where the second transistor M2 is located, depends on the transconductance g of the second transistor M2. m2 and resistance R L The product of resistance values. Specifically, the voltage gain of branch 207 where the second transistor M2 is located is: A V =g m2 ×R′ L

[0068] Among them, g m2 This is the transconductance of the second transistor M2. Here, since the signal does not flow through the first resistor R1, therefore, R′ L For the third transistor M3 and resistor R L The total equivalent impedance.

[0069] Here, the transconductance of a transistor can be expressed as:

[0070] In the above formula, K′ represents the physical parameters of the transistor, W / L represents the aspect ratio of the transistor, and I... DS This is the source leakage current.

[0071] Because the first capacitor C1 is provided in the branch 207 where the second transistor M2 is located, the impedance of the load in the branch 207 where the second transistor M2 is located decreases at high frequencies, that is, R′ L The amplification factor decreases, resulting in a reduction in the amplification factor of the branch 207 containing the second transistor M2. Since the filter circuit in this embodiment includes an active inductor 203, the amplification factor of the branch 207 containing the second transistor M2 is equal to the transconductance g of the second transistor M2. m2 With resistance R L The product of the inductive reactance of the active inductor 203 and the inductive reactance of the active inductor 203. This allows the amplification factor of the branch 207 containing the second transistor M2 to remain constant within a certain frequency range, improving the amplification effect at high frequencies. In summary, the active inductor 203 expands the bandwidth of the second transistor M2, enabling its amplification effect to cover higher frequencies. On the other hand, it also increases the total equivalent impedance of the branch 207 containing the second transistor M2 within a frequency band, thereby increasing the gain of this band and increasing the amplification factor of the first capacitor C1. This is beneficial for obtaining a lower inflection point frequency and reducing the swing caused by low-frequency ripple in the current at the current input point. Specifically, based on the impedance expression seen from the input terminal of the active inductor 203, a zero and a dominant pole can be obtained. When the frequency of the current signal is connected between the zero and the dominant pole, the active inductor 203 can increase the total equivalent impedance of the branch 207 containing the second transistor M2, thereby increasing the gain of this frequency band.

[0072] In this embodiment, the filter circuit further includes a second capacitor C2, the first terminal 210 of the second capacitor C2 is connected to the control terminal 211 and the output terminal 212 of the first transistor M1, and the second terminal 213 of the second capacitor C2 is grounded.

[0073] In this embodiment, since the branch 207 where the second transistor M2 is located has a certain bandwidth limitation, at frequencies higher than the bandwidth of the branch 207 where the second transistor M2 is located, the voltage gain A of the branch 207 where the second transistor M2 is located is... V The decrease in frequency causes the amplification effect of the first capacitor C1 to weaken. Therefore, for high-frequency signal filtering, the filter circuit can include a second capacitor C2 to improve the amplification effect of the branch 207 containing the second transistor M2 at high frequencies. Here, the first capacitor C1 and the active inductor 203 can form a first-stage filter in the filter circuit 200, and the second capacitor C2 can form a second-stage filter in the filter circuit 200. The second capacitor C2 does not affect the current replication of the current mirror, thus enabling filtering at different frequencies and achieving multi-pole filtering.

[0074] In this embodiment, the capacitance of the second capacitor C2 is smaller than that of the first capacitor C1. Because capacitors with different capacitance values ​​filter different frequency bands, and since the second capacitor C2 has a higher filtering frequency band, its capacitance can be designed to be smaller to save chip area.

[0075] At this point, the equivalent impedance of the filter circuit can be simplified to:

[0076] Among them, g m1 The transconductance of the first transistor M1 is given.

[0077] The 3dB inflection point frequency can be written as:

[0078] Here, since the first transistor M1 and the second transistor M2 constitute the first current mirror, the DC current I of the first transistor M1 and the second transistor M2 is... DS The ratio can be expressed by the width-to-length ratio of the first transistor M1 and the second transistor M2. When the voltage gain A... V When C2 is large and C2 is small, the above equation can be simplified to:

[0079] In this embodiment of the disclosure, through design This allows the first capacitor C1 to be amplified, thus enabling low-pass filtering with a lower inflection point frequency using a smaller area of ​​the first capacitor C1.

[0080] In this embodiment of the disclosure, the current signal I IN The current signal I is input from the first transistor M1.IN The ripple in the current flows away through the first capacitor C1 and the second capacitor C2, therefore the current signal I... IN Filtered. Filtered current I IN The current is copied by the second transistor M2, therefore the copying current flowing from the output terminal 205 of the second transistor M2 is also filtered; that is, the current in the branch containing the second transistor M2 is filtered. When the copying current flows through resistor R... L At that time, it is converted into a voltage signal V OUT V is output from voltage output terminal 214 OUT Voltage signal V OUT This is the filtered voltage signal. Here, the resistor R... L The size can be adjusted according to design requirements, allowing for flexible voltage signal V. OUT .

[0081] Referring to Figure 3, which is a circuit diagram of a second type of filter circuit provided in an embodiment of this disclosure.

[0082] As shown in Figure 3, in this embodiment of the present disclosure, the filter circuit 300 includes two current mirrors, a first capacitor C1, a second capacitor C2, an active inductor 306, a voltage conversion module 304, and a voltage output terminal 314. The two current mirrors are: a first current mirror formed by a first transistor M1 and a second transistor M2, and a second current mirror 303 formed by a first transistor M1 and a fourth transistor M4. The specific structures of the first transistor M1, the second transistor M2, the first capacitor C1, the second capacitor C2, the active inductor 306, and the voltage conversion module 304 can be referred to the relevant descriptions in Figure 2, and will not be repeated here.

[0083] In this embodiment, the structure of the second current mirror is illustrated using the structure of the basic current mirror. Specifically, the second current mirror includes a first transistor M1 and a fourth transistor M4. The control terminal of the fourth transistor M4 is connected to the control terminal 302 of the first transistor M1, and is used to process the input current signal I received by the first transistor M1. IN Perform a mirror copy. The copy ratio can be 1:M, where M can be greater than or less than 1. The copy ratios of the fourth transistor M4 and the second transistor M2 can be the same or different.

[0084] In this embodiment, the voltage conversion module 304 is connected to the output terminal 305 of the fourth transistor M4, and is used to convert the output of the fourth transistor M4 into a voltage signal V. OUT The voltage is then output from the voltage output terminal 314.

[0085] It should be noted that the low-pass filtering of the filter circuit 300 in Figure 3 is achieved through a first current mirror formed by the first transistor M1 and the second transistor M2, as well as the first capacitor C1, the second capacitor C2, the active inductor 306, and the second resistor R2. The voltage conversion of the filter circuit 300 is achieved through a second current mirror 303 formed by the first transistor M1 and the fourth transistor M4, as well as the voltage conversion module 304 and the voltage output terminal 314.

[0086] In this embodiment, compared to the filter circuit 200 shown in FIG2, in the filter circuit 300 of FIG3, the voltage output terminal 314 is connected to the branch where the fourth transistor M4 is located, the first capacitor C1 and the active inductor 306 are connected to the branch where the second transistor M2 is located, and the voltage output terminal 314, the first capacitor C1 and the active inductor 306 are connected to different output branches of the current mirror, which can realize the output voltage V OUT The filter structure (formed by the first capacitor C1 and the active inductor 306) is separated from the filter structure, thus giving both more design flexibility.

[0087] In this embodiment, the first transistor M1 and the fourth transistor M4 form a second current mirror 303. Here, the current flowing into the first transistor M1 is the filtered current. In other words, the input current signal I... IN The ripple above the mid-inflection point frequency has actually flowed away through the first capacitor C1 and the second capacitor C2, and has not flowed into the first transistor M1. Therefore, the fourth transistor M4 can replicate the current flowing into the first transistor M1 and output it from its output terminal 305. Furthermore, the voltage conversion module 304 connected to the output terminal 305 of the fourth transistor M4 can convert the current signal output by the fourth transistor M4 into a voltage signal V. OUT And output the voltage signal V through the voltage output terminal 314. OUT Implement filtering.

[0088] In this embodiment, the filter circuit 300 further includes a second resistor R2 connected in series with the active inductor 306. The resistance value of the second resistor R2 is greater than the resistance value of the voltage conversion module 304. Specifically, the resistance value of the second resistor R2 is greater than that of the resistor R. L The resistance value. In this embodiment of the present disclosure, the second resistor R2 can be used as part of the load of the branch 307 where the second transistor M2 is located, so as to increase the impedance value of the load of the branch 307 where the second transistor M2 is located, thereby increasing the amplification factor of the first capacitor C1, which is beneficial to obtaining a lower inflection point frequency.

[0089] It should be noted that the branch containing the second transistor M2, active inductor 306, and second resistor R2 in Figure 3 serves the same function as the branch containing the second transistor M2, active inductor 203, and voltage conversion module 206 in Figure 2: amplifying the first capacitor C1 to achieve low-pass filtering. However, since the branch containing the second transistor M2, active inductor 306, and second resistor R2 in Figure 3 does not require an output voltage V... OUT Therefore, it will not affect the normal operation of the branch 307 where the second transistor M2 is located. Thus, the second resistor R2 can be appropriately increased to obtain a larger capacitance amplification factor. In this embodiment, the resistance value of the second resistor R2 is greater than the resistance value of the voltage conversion module 304; for example, the resistance value of the second resistor R2 is greater than that of the resistor R... L The resistance value is adjusted to achieve better amplification of the capacitor.

[0090] In some embodiments of this disclosure, the active inductor 306 is connected between the second resistor R2 and the second transistor M2. In other embodiments of this disclosure, the second resistor R2 may be connected between the active inductor 306 and the second transistor M2, thereby making it easier to connect the output terminal 308 (e.g., the source of the third transistor M3) and the body of the third transistor M3 to the same potential. Specifically, the second resistor R2 is connected between the input terminal of the active inductor 306 and the output terminal of the second transistor M2, and the output terminal 308 of the third transistor M3 is grounded.

[0091] In Figure 3, the first transistor M1, the second transistor M2, and the fourth transistor M4 are all PMOS transistors. The input terminal 309 of the first transistor M1 (e.g., the source of the first transistor M1), the input terminal 310 of the second transistor M2 (e.g., the source of the second transistor M2), and the input terminal of the fourth transistor M4 (e.g., the source of the third transistor M4) are connected to the operating voltage V. DD One end of the second resistor R2 and one end of the voltage conversion module 304 are grounded. The other end of the voltage conversion module 304 (the end connected to the voltage output terminal 314) is connected to the output terminal 305 of the fourth transistor M4. The voltage output terminal 314 is used to output voltage V. OUT .

[0092] In this embodiment of the disclosure, the control terminals of the second transistor M2 and the fourth transistor M4 are connected to the same node. Specifically, the control terminals of the second transistor M2 and the fourth transistor M4 are connected to the node connected to the control terminal 302 of the first transistor M1.

[0093] In some embodiments of this disclosure, the control terminals of the first transistor M1, the fourth transistor M4, and the second transistor M2 are connected in sequence. For example, as shown in FIG3, the control terminal of the fourth transistor M4 is closer to the control terminal of the first transistor M1. That is, in the circuit layout, the control terminal of the fourth transistor M4 is connected between the control terminals of the first transistor M1 and the control terminals of the fourth transistor M4.

[0094] In other embodiments of this disclosure, the control terminals of the first transistor M1, the second transistor M2, and the fourth transistor M4 may be connected sequentially, with the control terminal of the second transistor M2 being closer to the control terminal of the first transistor M1. That is, in the circuit layout, the control terminal of the second transistor M2 is connected between the control terminals of the first transistor M1 and the fourth transistor M4.

[0095] Referring to Figure 4, which is a circuit diagram of a third type of filter circuit provided in an embodiment of this disclosure.

[0096] As shown in Figure 4, in this embodiment of the present disclosure, the filter circuit 400 includes a first transistor M1, a second transistor M2, a fourth transistor M4, a first capacitor C1, a second capacitor C2, an active inductor 406, a voltage conversion module 405, a voltage output terminal 414, and a second resistor R2. The first transistor M1 and the second transistor M2 form a first current mirror, and the first transistor M1 and the fourth transistor M4 form a second current mirror. The specific structures of the first current mirror, the first transistor M1, the second transistor M2, the first capacitor C1, the second capacitor C2, the active inductor 406, and the voltage conversion module 405 can be referred to the relevant description in Figure 2. The second current mirror, the fourth transistor M4, and the second resistor R2 can be referred to the description in Figure 3, and will not be repeated here.

[0097] In this embodiment, the filter circuit 400 further includes at least one filter unit 401 connected between the control terminal 402 of the second transistor M2 and the control terminal 403 of the fourth transistor M4. The control terminal 404 of the first transistor M1, the control terminal 402 of the second transistor M2, the filter unit 401, and the control terminal 403 of the fourth transistor M4 are connected in sequence. For example, as shown in FIG4, the control terminal of the second transistor M2 is closer to the control terminal of the first transistor M1. That is, in the circuit layout, the control terminal 402 of the second transistor M2 is connected between the control terminal 404 of the first transistor M1 and the control terminal 403 of the fourth transistor M4.

[0098] The filtering frequency of the filter unit 401 can be different from the filtering frequency of the filter structure formed by the first capacitor C1 and the active inductor 406 to achieve multi-pole filtering. Here, the filter unit 401 can form a third-stage filter in the filter circuit 400. In addition, when the filter circuit 400 includes multiple filter units 401 connected in series, the multiple filter units 401 connected in series can be used for filtering at different frequencies.

[0099] In this embodiment, at least one filter unit 401 is connected between the control terminal 402 of the second transistor M2 and the control terminal 403 of the fourth transistor M4. Here, the filter unit 401 can be an RC filter module or an LC filter module. In Figure 4, the filter unit 401 may include at least one RC filter module, for example, the filter unit 401 includes a resistor R. F and a capacitor C F This achieves multi-pole filtering. It's important to note that filter unit 401 filters the voltage at the control terminal 402 of the second transistor M2, not the current. Therefore, filter unit 401 can use a relatively large resistor R. F Instead of a large capacitor C F To obtain a low inflection point frequency, so as to reduce the capacitance C F The area will not affect the input current I. IN The voltage swing of the input node.

[0100] In this embodiment of the disclosure, the current signal I IN The ripple in the middle passes through the first capacitor C1, the second capacitor C2, and the capacitor C. F The current flows away, therefore the current signal I IN Filtered. Filtered current I IN The current is copied by the fourth transistor M4, therefore the copying current flowing from the output of the fourth transistor M4 is also filtered; that is, the copying current in the branch containing the fourth transistor M4 is filtered. When the copying current flows through resistor R... L At that time, it is converted into a voltage signal V OUT V is output from voltage output terminal 414 OUT Voltage signal V OUT This is the filtered voltage signal.

[0101] In this embodiment of the disclosure, when the filter circuit 400 includes a filter unit 401, the branch containing the fourth transistor M4 and the voltage conversion module 405 needs to be located after the filter unit 401. That is, along the current transmission direction, the voltage conversion module 405 is connected after the filter unit 401 to ensure that the second current mirror can perform the function of current replication.

[0102] In this embodiment, the size of the first transistor M1 is smaller than the size of the second transistor M2, so as to amplify the first capacitor C1. The size of the transistor can be understood as the aspect ratio of its gate.

[0103] In this embodiment of the disclosure, the relative size of the fourth transistor M4 and the first transistor M1 can be adjusted according to actual needs. This can be understood as adjusting the relative size of the aspect ratio of the fourth transistor M4 and the aspect ratio of the first transistor M1.

[0104] In the embodiments shown in Figures 2 to 4 above, the first transistor M1, the second transistor M2, and the fourth transistor M4 can be MOS transistors or BJT transistors. In the above embodiments, the first transistor M1, the second transistor M2, and the fourth transistor M4 are all described using PMOS transistors as examples. However, in other embodiments, the first transistor M1, the second transistor M2, and the fourth transistor M4 can all be NMOS transistors. In Figure 5, Figure 4 will be used as an example to specifically illustrate the structure of the filter circuit 500 after replacing the first transistor M1, the second transistor M2, and the fourth transistor M4 in Figure 4 with NMOS transistors.

[0105] Referring to Figure 5, which is a circuit diagram of the fourth filtering circuit provided in the embodiments of this disclosure.

[0106] As shown in Figure 5, the first transistor M1, the second transistor M2, and the fourth transistor M4 are NMOS transistors. It is understandable that, due to the change in the type of each transistor, the filter circuit 500 in Figure 5 needs to mirror-flip the active portion of the PMOS transistors compared to the filter circuit 400 in Figure 4. At this time, the input terminal 501 of the first transistor M1 (e.g., the source of the first transistor M1), the input terminal 502 of the second transistor M2 (e.g., the source of the second transistor M2), and the input terminal 503 of the fourth transistor M4 (e.g., the source of the third transistor M3) are respectively grounded. One end of the second resistor R2 and one end of the voltage conversion module 504 are connected to the operating voltage V. DD Furthermore, the other end of the voltage conversion module 504 (the end connected to the voltage output terminal 514) is connected to the output terminal of the fourth transistor M4, and the voltage output terminal 514 is used to output voltage V. OUT .

[0107] In this embodiment, the first current mirror includes a base current mirror, a cascode current mirror, or a self-biased cascaded current mirror. The second current mirror includes a base current mirror, a cascode current mirror, or a self-biased cascaded current mirror. The first and second current mirrors share a first transistor M1. The following description uses the first current mirror as an example to illustrate the possible structures of the first and second current mirrors.

[0108] Referring to Figures 6 to 8, Figure 6 is a schematic diagram of a first type of first current mirror provided by an embodiment of the present disclosure, Figure 7 is a schematic diagram of a second type of first current mirror provided by an embodiment of the present disclosure, and Figure 8 is a schematic diagram of a third type of first current mirror provided by an embodiment of the present disclosure.

[0109] As shown in Figure 6, the first current mirror 600 is an improvement on the basic current mirror. The first current mirror 600 includes a first transistor M1, a second transistor M2, resistors R3 and R4. The first transistor M1 and the second transistor M2 can be PMOS transistors. The input terminal 601 of the first transistor M1 (e.g., the source of the first transistor M1) is connected to the operating voltage V via resistor R3. DD The input terminal 602 of the first transistor M2 (e.g., the source of the second transistor M2) is connected to the operating voltage V via resistor R4. DD In other embodiments, the first transistor M1 and the second transistor M2 may also be NMOS transistors. The first transistor M1 of the first current mirror 600 is used to receive the input current I. IN A first capacitor C1 can be connected between the control terminal and the output terminal of the second transistor M2 of the first current mirror 600. When the current mirror shown in Figure 6 is applied to the second current mirror, the second transistor M2 in Figure 6 can be replaced with the fourth transistor M4.

[0110] As shown in Figure 7, the second type of first current mirror 700 is a common-source, common-gate current mirror. The first current mirror 700 includes a first transistor M1, a second transistor M2, a fifth transistor M5, and a sixth transistor M6. The first transistor M1, second transistor M2, fifth transistor M5, and sixth transistor M6 can be PMOS transistors. The input terminal 701 of the first transistor M1 is connected to the output terminal 702 of the fifth transistor M5, and the input terminal 703 of the fifth transistor M5 is connected to the operating voltage V. DD The input terminal 704 of the second transistor M2 is connected to the output terminal 705 of the sixth transistor M6, and the input terminal 706 of the sixth transistor M6 is connected to the operating voltage V. DD In other embodiments, the first transistor M1, the second transistor M2, the fifth transistor M5, and the sixth transistor M6 may also be NMOS transistors.

[0111] The first transistor M1 of the first current mirror 700 is used to receive the input current I. IN A first capacitor C1 can be connected between the control terminal and the output terminal of the second transistor M2 of the first current mirror 700. When the current mirror shown in Figure 7 is applied to the second current mirror, the second transistor M2 in Figure 7 can be replaced with the fourth transistor M4.

[0112] In the embodiment shown in Figure 7, the input terminal 703 and the output terminal 702 of the fifth transistor M5 are connected to the operating voltage V. DD Between the input terminal of the first transistor M1 and the input terminal of the sixth transistor M6, the input terminal 706 and the output terminal 705 are connected to the operating voltage V. DD In other embodiments, the input and output terminals of the first transistor M1 can also be connected to the operating voltage V between the input terminal of the second transistor M2 and the input terminal of the second transistor M2. DD Between the input terminal of the fifth transistor M5 and the input terminal of the second transistor M2, the input and output terminals of the sixth transistor M6 are connected to the input terminal of the sixth transistor M6 and the operating voltage V. DD between.

[0113] As shown in Figure 8, the third type of first current mirror 800 is a self-biased cascaded current mirror. The first current mirror 800 includes a first transistor M1, a second transistor M2, a fifth transistor M5, a sixth transistor M6, and a resistor R5. The first transistor M1, second transistor M2, fifth transistor M5, and sixth transistor M6 can be PMOS transistors. The input terminal 801 of the first transistor M1 is connected to the output terminal 802 of the fifth transistor M5, and the input terminal 803 of the fifth transistor M5 is connected to the operating voltage V. DD The input terminal 804 of the second transistor M2 is connected to the output terminal 805 of the sixth transistor M6, and the input terminal 806 of the sixth transistor M6 is connected to the operating voltage V. DD The control terminal 807 of the first transistor M1 (e.g., the gate of the first transistor M1) is connected to one end of the resistor R5, and the control terminal 808 of the fifth transistor M5 (e.g., the gate of the fifth transistor M5) is connected to the other end of the resistor R5. In other embodiments, the first transistor M1, the second transistor M2, the fifth transistor M5, and the sixth transistor M6 may also be NMOS transistors.

[0114] The first transistor M1 of the first current mirror 800 is used to receive the input current I. IN Input current I IN The first capacitor C1 can be connected between the control terminal and the output terminal of the second transistor M2 of the first current mirror 800, which can be connected from one end of the resistor R5. When the current mirror shown in Figure 8 is applied to the second current mirror, the second transistor M2 in Figure 8 can be replaced with the fourth transistor M4.

[0115] In the embodiment shown in Figure 8, the input and output terminals of the fifth transistor M5 are connected to the operating voltage V. DD The input and output terminals of the sixth transistor M6 are connected to the operating voltage V between the input terminal of the first transistor M1 and the input terminal of the first transistor M1. DD In other embodiments, the input and output terminals of the first transistor M1 can also be connected to the operating voltage V between the input terminal 804 of the second transistor M2 and the input terminal 804 of the second transistor M2.DD Between the input terminal of the fifth transistor M5 and the input terminal of the second transistor M2, the input and output terminals of the sixth transistor M6 are connected to the input terminal of the sixth transistor M6 and the operating voltage V. DD between.

[0116] In this embodiment of the disclosure, the first current mirror can be replaced with any of the current mirror structures shown in Figures 6 to 8 according to design requirements in order to obtain better replication accuracy.

[0117] In addition, in the embodiments of this disclosure, the first current mirror in the filter circuit does not provide current-to-output voltage V. OUT The function, that is, the output voltage V OUT Generated by the voltage conversion module, it separates the low-pass filtering and current-to-voltage conversion processes, improving the flexibility of circuit design.

[0118] It should be understood that the phrase "an embodiment" or "one embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this disclosure. Therefore, "in one embodiment" or "one embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. It should be understood that in the various embodiments of this disclosure, the sequence numbers of the above-described processes do not imply a sequential order of execution; the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this disclosure. The sequence numbers of the above-described embodiments are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0119] The above description is merely a preferred embodiment of this disclosure and does not limit the patent scope of this disclosure. Any equivalent structural transformations made using the contents of this specification and drawings under the inventive concept of this disclosure, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this disclosure.

Claims

1. A filter circuit, characterized in that, include: At least one current mirror is used to mirror and replicate current; the at least one current mirror includes a first current mirror, the first current mirror includes a first transistor and a second transistor, the second transistor is used to mirror and replicate the input current signal received by the first transistor; A first capacitor is connected between the control terminal and the output terminal of the second transistor; An active inductor is connected to the output terminal of the second transistor; A voltage conversion module is used to convert the mirrored current of one of the current mirrors into a voltage signal; The voltage output terminal is used to output the converted voltage signal.

2. The filter circuit according to claim 1, characterized in that, The second transistor amplifies the capacitance value of the first capacitor.

3. The filter circuit according to claim 1, characterized in that, The active inductor includes a first resistor and a third transistor. The first resistor is located between the control terminal and the input terminal of the third transistor, and the input terminal of the third transistor is connected to the output terminal of the second transistor.

4. The filter circuit according to claim 1, characterized in that, The voltage conversion module is used to convert the mirrored current of the first current mirror into the voltage signal, and the voltage conversion module is connected to the output terminal of the second transistor; The voltage output terminal is connected to the output terminal of the second transistor.

5. The filter circuit according to claim 1, characterized in that, The at least one current mirror further includes a second current mirror: The second current mirror includes a first transistor and a fourth transistor, wherein the fourth transistor is used to mirror the input current signal received by the first transistor.

6. The filter circuit according to claim 5, characterized in that, The voltage conversion module is used to convert the mirrored current of the second current mirror into the voltage signal, and the voltage conversion module is connected to the output terminal of the fourth transistor; The voltage output terminal is connected to the output terminal of the fourth transistor.

7. The filter circuit according to claim 5 or 6, characterized in that, Also includes: At least one filtering unit is provided, wherein the control terminal of the first transistor, the control terminal of the second transistor of the first current mirror, the filtering unit, and the control terminal of the fourth transistor are connected in sequence.

8. The filter circuit according to claim 7, characterized in that, It also includes a second resistor connected in series with the active inductor, the resistance of the second resistor being greater than the resistance of the voltage conversion module.

9. The filter circuit according to claim 1, characterized in that, The voltage conversion module includes a resistor or a transimpedance amplifier.

10. The filter circuit according to claim 1, characterized in that, The first transistor and the second transistor include MOS transistors or BJT transistors.

11. The filter circuit according to claim 1, characterized in that, The size of the first transistor is smaller than the size of the second transistor.

12. The filter circuit according to claim 1, characterized in that, The filtering circuit also includes: The second capacitor has its first terminal connected to the control terminal and output terminal of the first transistor, and its second terminal grounded.

13. The filter circuit according to claim 12, characterized in that, The capacitance of the second capacitor is less than that of the first capacitor.

14. The filter circuit according to claim 1, characterized in that, The first current mirror includes a base current mirror, a common-source cascode current mirror, or a self-biased cascaded current mirror.

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