Bandpass filter and oscillator circuit

Abstract

The present application provides a bandpass filter, which includes: an input circuit for converting an input voltage signal into a current signal and then outputting it; a load circuit connected to the input circuit for receiving a voltage signal of the current signal to form a first-order RC characteristic; an adjustment circuit connected to the load circuit for adjusting the high-frequency characteristics and quality factor of the bandpass filter based on the voltage signal; a feedback circuit, wherein the input end of the feedback circuit is connected to the output end of the adjustment circuit, and the output end of the feedback circuit is connected to the input end of the input circuit, for feeding back the low-frequency part of the output signal of the adjustment circuit to the input circuit. The bandpass filter of the present application adopts a fully differential structure, has good common-mode rejection characteristics and anti-interference characteristics, a simple structure, low equivalent input noise, can provide an in-band gain of about 50dB, realizes a third-order characteristic, and has an attenuation characteristic of ‑40dB / DEC outside the high-frequency band.

Description

Technical Field

[0001] The present application relates to the field of circuit technology, and in particular to a bandpass filter and an oscillation circuit. Background Art

[0002] A band-pass filter is a filter that can pass frequency components within a certain frequency range, but attenuate frequency components in other ranges to a very low level. Usually, a band-pass filter needs to be used in conjunction with a single low-noise amplifier, which generally cannot provide a large gain in the selected passband and often requires an additional gain stage. Summary of the invention

[0003] The purpose of the embodiments of the present application is to provide a bandpass filter to improve the working performance of the bandpass filter.

[0004] In a first aspect, an embodiment of the present application provides a bandpass filter, comprising: an input circuit, for converting an input voltage signal into a current signal and then outputting the converted current signal; a load circuit, connected to the input circuit, for receiving the current signal and generating a voltage signal; a regulation circuit, connected to the load circuit, for adjusting the high-frequency characteristics and quality factor of the bandpass filter based on the voltage signal; and a feedback circuit, wherein the input end of the feedback circuit is connected to the output end of the regulation circuit, and the output end of the feedback circuit is connected to the input end of the input circuit, for feeding back the output signal of the regulation circuit to the input circuit.

[0005] In one embodiment, the input circuit is a fully differential high-pass circuit.

[0006] In one embodiment, the input circuit includes: a first transconductance amplifier; a first capacitor connected to a first non-inverting input terminal of the first transconductance amplifier; a first resistor connected to the first non-inverting input terminal of the first transconductance amplifier; a second capacitor connected to a first inverting input terminal of the first transconductance amplifier; and a second resistor connected to a first inverting input terminal of the first transconductance amplifier.

[0007] In one embodiment, the load circuit is a fully differential low-pass circuit.

[0008] In one embodiment, the load circuit includes: a second transconductance amplifier, wherein the non-inverting input terminal of the second transconductance amplifier is connected to the inverting output terminal of the first transconductance amplifier, and the inverting input terminal of the second transconductance amplifier is connected to the non-inverting output terminal of the first transconductance amplifier; a first filtering module, wherein one end is connected to the non-inverting input terminal of the second transconductance amplifier, and the other end is connected to the inverting output terminal of the second transconductance amplifier; and a second filtering module, wherein one end is connected to the inverting input terminal of the second transconductance amplifier, and the other end is connected to the non-inverting output terminal of the second transconductance amplifier.

[0009] In one embodiment, the regulating circuit is a fully differential low-pass circuit.

[0010] In one embodiment, the regulation circuit includes: a third transconductance amplifier, wherein the non-inverting input terminal of the third transconductance amplifier is connected to the inverting output terminal of the second transconductance amplifier, and the inverting input terminal of the third transconductance amplifier is connected to the non-inverting output terminal of the second transconductance amplifier; a first resistor-capacitor circuit, wherein one end is connected to the non-inverting input terminal of the third transconductance amplifier, and the other end is connected to the inverting output terminal of the third transconductance amplifier; and a second resistor-capacitor circuit, wherein one end is connected to the inverting input terminal of the third transconductance amplifier, and the other end is connected to the non-inverting output terminal of the third transconductance amplifier.

[0011] In one embodiment, the first resistor-capacitor circuit includes: a third resistor; a fourth resistor, a first connection point of which is connected in parallel with the third resistor and is connected to the inverting output terminal of the third transconductance amplifier; a fifth resistor, connected to a second connection point formed by connecting the third resistor and the fourth resistor; a third capacitor, one end of which is connected to the second connection point and the other end of which is connected to the non-inverting input terminal of the third transconductance amplifier and is connected in parallel with the fifth resistor; a sixth resistor, one end of which is connected to the fifth resistor and the other end of which is connected to the non-inverting input terminal of the third transconductance amplifier.

[0012] In one embodiment, the second RC circuit and the first RC circuit have the same circuit structure.

[0013] In one embodiment, the feedback circuit includes: a third resistor-capacitor circuit, one end of which is connected to the non-inverting output terminal of the third transconductance amplifier, and the other end is connected to the second inverting input terminal of the first transconductance amplifier; a fourth resistor-capacitor circuit, one end of which is connected to the inverting output terminal of the third transconductance amplifier, and the other end is connected to the second non-inverting input terminal of the first transconductance amplifier.

[0014] The bandpass filter provided in the present application adopts a fully differential structure, and has good common-mode rejection and anti-interference characteristics; combined with a low-noise input stage, it has a simple structure and low equivalent input noise; it can provide an in-band gain of about 50dB; it realizes a third-order characteristic, has an attenuation characteristic of -40dB / DEC outside the high-frequency band, and has good suppression. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1This is a schematic structural diagram of a bandpass filter according to an embodiment of the present application;

[0017] Figure 2 This is a schematic structural diagram of a bandpass filter according to an embodiment of the present application;

[0018] Figure 3 This is a structural schematic diagram of a first transconductance amplifier according to an embodiment of the present application;

[0019] Figure 4 Schematic diagram of the structure of a second transconductance amplifier according to an embodiment of the present application.

[0020] Reference numerals:

[0021] 1-bandpass filter, 10-input circuit, 20-load circuit, 30-regulation circuit, 40-feedback circuit, A1-first transconductance amplifier, C1-first capacitor, R1-first resistor, C2-second capacitor, R2-second resistor, P1-first non-inverting input terminal of the first transconductance amplifier, P2-second non-inverting input terminal of the first transconductance amplifier, N1-first inverting input terminal of the first transconductance amplifier, N2-second inverting input terminal of the first transconductance amplifier, U1-inverting output terminal of the first transconductance amplifier, U2-non-inverting output terminal of the first transconductance amplifier, P3-non-inverting input terminal of the second transconductance amplifier, N3-inverting input terminal of the second transconductance amplifier, U3-inverting output terminal of the second transconductance amplifier, U4-non-inverting output terminal of the second transconductance amplifier, 21-first filtering module, 22-second filtering module, 31-first resistor-capacitor circuit, 32-second resistor-capacitor circuit, 41-third resistor-capacitor circuit, 42-fourth resistor-capacitor circuit. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings in the embodiments of the present application. In the description of the present application, the terms "first", "second" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0023] like Figure 1 As shown, this embodiment provides a bandpass filter 1, including: an input circuit 10, a load circuit 20, a regulating circuit 30 and a feedback circuit 40, wherein:

[0024] The input circuit 10 is used to convert the input voltage signal into a current signal and then output it. The input circuit 10 can be a fully differential high-pass input module, which converts the input differential voltage signal into an output differential current signal.

[0025] The load circuit 20 is connected to the input circuit 10, and is used to receive the current signal and perform gain processing on the current signal to generate a gain signal. The load circuit 20 can be a fully differential low-pass gain module, which converts the differential current signal output by the input circuit 10 into a differential voltage signal through negative feedback, and realizes differential signal gain in conjunction with the input circuit 10.

[0026] The adjustment circuit 30 is connected to the load circuit 20 and is used to adjust the quality factor of the bandpass filter 1 based on the gain signal. The adjustment circuit 30 can be a fully differential second-order low-pass module, which can realize two poles with a large adjustable range of Q value, thereby realizing differential high-impedance characteristics. Wherein Q is the quality factor of the filter, which can be expressed by the ratio of the center frequency F (unit HZ) of the filter to the -3dB bandwidth B (unit HZ), that is, Q = F / B, which describes the ability of the filter to separate adjacent frequency components in the signal. The larger the quality factor Q, the higher the resolution of the filter.

[0027] The input end of the feedback circuit 40 is connected to the output end of the regulating circuit 30, and the output end of the feedback circuit 40 is connected to the input end of the input circuit 10, for feeding back the output signal of the regulating circuit 30 to the input circuit 10. The feedback circuit 40 can be a fully differential low-pass feedback path, which can determine the DC operating point of the differential component of the output signal.

[0028] like Figure 2 As shown, this embodiment provides a bandpass filter 1, wherein the input circuit 10 can be implemented by: a first transconductance amplifier A1 and its peripheral resistor-capacitor network, the resistor-capacitor network can include a first capacitor C1, a first resistor R1, a second resistor R2 and a second capacitor C2, wherein the first capacitor C1 is connected to the first non-inverting input terminal P1 of the first transconductance amplifier A1. The first resistor R1 is connected to the first non-inverting input terminal P1 of the first transconductance amplifier A1. The second capacitor C2 is connected to the first inverting input terminal N1 of the first transconductance amplifier A1. The second resistor R2 is connected to the first inverting input terminal N1 of the first transconductance amplifier A1.

[0029] In one embodiment, the load circuit 20 includes: a second transconductance amplifier A2, wherein the non-inverting input terminal P3 of the second transconductance amplifier A2 is connected to the inverting output terminal U1 of the first transconductance amplifier A1, and the inverting input terminal N3 of the second transconductance amplifier A2 is connected to the non-inverting output terminal U2 of the first transconductance amplifier A1. A first filter module 21, wherein one end is connected to the non-inverting input terminal P3 of the second transconductance amplifier A2, and the other end is connected to the inverting output terminal U3 of the second transconductance amplifier A2. A second filter module 22, wherein one end is connected to the inverting input terminal N3 of the second transconductance amplifier A2, and the other end is connected to the non-inverting output terminal U4 of the second transconductance amplifier A2.

[0030] In one embodiment, the first filtering module 21 is composed of a capacitor C3 and a resistor R3.

[0031] In one embodiment, the second filtering module 22 is composed of a capacitor C4 and a resistor R4.

[0032] In one embodiment, the regulating circuit 30 includes: a third transconductance amplifier A3, wherein the non-inverting input terminal of the third transconductance amplifier A3 is connected to the inverting output terminal U3 of the second transconductance amplifier A2, and the inverting input terminal of the third transconductance amplifier A3 is connected to the non-inverting output terminal U4 of the second transconductance amplifier A2. A first resistor-capacitor circuit 31, wherein one end is connected to the non-inverting input terminal of the third transconductance amplifier A3, and the other end is connected to the inverting output terminal of the third transconductance amplifier A3. A second resistor-capacitor circuit 32, wherein one end is connected to the inverting input terminal of the third transconductance amplifier A3, and the other end is connected to the non-inverting output terminal of the third transconductance amplifier A3.

[0033] The first resistor-capacitor circuit 31 includes: a third resistor R5. A fourth resistor R6, a first connection point of which is connected in parallel with the third resistor R5 and connected to the inverting output terminal of the third transconductance amplifier A3. A fifth resistor R7, connected to a second connection point formed by connecting the third resistor R5 and the fourth resistor R6. A third capacitor C5, one end of which is connected to the second connection point and the other end of which is connected to the non-inverting input terminal of the third transconductance amplifier A3 and connected in parallel with the fifth resistor R7. A sixth resistor R8, one end of which is connected to the fifth resistor R7 and the other end of which is connected to the non-inverting input terminal of the third transconductance amplifier A3.

[0034] The second RC circuit 32 is composed of a resistor R9 , a resistor R10 , a resistor R11 , a resistor R12 and a capacitor C6 , and has the same circuit structure as the first RC circuit 31 .

[0035] In one embodiment, the regulating circuit 30 further includes a filtering module composed of a resistor R13 and a capacitor C7 , and a filtering module composed of a resistor R14 and a capacitor C8 .

[0036] In one embodiment, the RC network in the regulating circuit 30 may be a first-order low-pass network, which can reduce the ability to suppress high frequencies outside the band and also achieve the purpose of band-pass filtering.

[0037] In one embodiment, the feedback circuit 40 includes: a third resistor-capacitor circuit 41, one end of which is connected to the in-phase output terminal of the third transconductance amplifier A3, and the other end of which is connected to the second inverting input terminal N2 of the first transconductance amplifier A1. A fourth resistor-capacitor circuit 42, one end of which is connected to the inverting output terminal of the third transconductance amplifier A3, and the other end of which is connected to the second in-phase input terminal P2 of the first transconductance amplifier A1. No DC current flows through the resistor in the feedback circuit 40, so the DC voltage drop is zero, so the DC voltage at the second in-phase input terminal P2 and the second inverting input terminal N2 of the first transconductance amplifier A1 is determined by the DC voltage at the output point of the third transconductance amplifier A3, so the feedback circuit 40 can determine the low-frequency DC operating point of the differential component of the output signal.

[0038] like Figure 3 As shown, this embodiment provides a first transconductance amplifier A1 for input circuit 10, including transistors Q1 to Q12, current source SRC1 and current source SRC2, wherein: transistors Q1 and Q2 form a first group of differential input stages working in common source mode, transistors Q3 and Q4 form a second group of differential input stages working in common source mode, and the two groups of differential input stages of transistors Q1, Q2 and transistors Q3 and Q4 convert the input differential voltage into differential current and work in an open loop state. Transistors Q5 and Q6 form a group of differential current loads, which function to provide operating points for transistors Q1 to Q4, and at the same time, as part of the common mode negative feedback loop, adjust the output common mode operating point of this stage. Transistors Q7 and Q8 work in common gate mode, which function to increase the output impedance and make the output closer to the ideal current source. Similarly, transistors Q9 and Q10 also work in the common-gate mode, and cooperate with transistors Q11 and Q12 to form a differential common-source common-gate load.

[0039] The input circuit 10 composed of the first transconductance amplifier A1 has the following characteristics:

[0040] Its feature 1 is that it works in open-loop mode, and after the differential input voltage is converted into an output differential current by the first transconductance amplifier A1, it all flows through the resistance of the load circuit 20. Feature 2 is that the common-mode output point is determined by the common-mode negative feedback. Feature 3 is that the transconductance of the input tube is greater than the transconductance of the load tube, thereby achieving the purpose of low equivalent input noise. Feature 4 is that the output current and the output of the feedback circuit 40 are superimposed. Among them, the transistors Q1 to Q4 can be one or more of MOS tubes (Metal Oxide Semiconductor, Metal Oxide Semiconductor Field Effect Transistor), JFET (Junction Field-Effect Transistor, Junction Field Effect Transistor, referred to as "JFET"), BJT tubes (Bipolar Junction Transistor, Bipolar Junction Transistor, referred to as "BJT"), and the transistors Q5 to Q12 are field effect transistors.

[0041] like Figure 4 As shown, this embodiment provides a second transconductance amplifier A2 for a load circuit 20, including: transistors Q13 to Q25, and a current source SRC3, wherein transistors Q13 and Q14 constitute a differential input stage in a common source state. Transistors Q15 and Q16 constitute a differential current load, and at the same time control the output common mode operating point as part of a common mode negative feedback loop. Transistors Q17 and Q18 operate in a common gate state to increase the output impedance and the DC gain of the loop. Transistors Q19 to Q22 constitute a common source and common gate differential load. The above-mentioned transistors Q13 to Q22 constitute the first stage of the above-mentioned second transconductance amplifier A2. Transistors Q23 and Q24 constitute a common source differential output tube, and transistors Q25 and Q26 constitute a differential current load. The above-mentioned transistors Q23 to Q26 constitute the second stage of the above-mentioned second transconductance amplifier A2.

[0042] The second transconductance amplifier A2 is a fully differential operational amplifier, which realizes the load circuit 20 in combination with external passive resistors and capacitors, and has the following characteristics:

[0043] 1. Working in closed-loop mode, the resistor and capacitor absorb the current from the open-loop output of the input circuit 10. 2. Its common-mode output point is determined by its own common-mode negative feedback.

[0044] In one embodiment, the third transconductance amplifier A3 in the regulating circuit 30 may have the same internal structure as the second transconductance amplifier A2. That is, the regulating circuit 30 may be implemented by a fully differential operational amplifier combined with external passive resistors and capacitors, and its common-mode output point is determined by its own common-mode negative feedback.

[0045] In one embodiment, the feedback circuit 40 is implemented by a differential input stage and an external low-pass RC network.

[0046] In one embodiment, in the input circuit 10 and / or the feedback circuit 40, the input device for converting voltage into current may be one or more of a P-type enhancement MOS transistor, an N-type enhancement MOS transistor, a PNP bipolar transistor, an NPN bipolar transistor, and a J-type field effect transistor.

[0047] In one embodiment, the fully differential voltage-to-current conversion circuit and the fully differential operational amplifier involved in the input circuit 10, the load circuit 20, and the adjustment circuit 30 can be implemented in a variety of ways, such as a basic common-source input, and can adopt one or more of a common-source load operational amplifier, a sleeve common-source common-gate operational amplifier, and a folded common-source common-gate operational amplifier.

[0048] The above-mentioned bandpass filter 1 adopts a fully differential structure, has good common-mode suppression characteristics and anti-interference characteristics; combined with a low-noise input stage, it has a simple structure and low equivalent input noise; it can provide an in-band gain of about 50dB; it realizes a third-order characteristic, has an attenuation characteristic of -40dB / DEC outside the high-frequency band, and has good suppression.

[0049] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A bandpass filter, characterized in that: include: An input circuit, the input circuit comprising: a first transconductance amplifier; a first capacitor connected to a first non-inverting input terminal of the first transconductance amplifier; a first resistor connected to a first non-inverting input terminal of the first transconductance amplifier; a second capacitor connected to a first inverting input terminal of the first transconductance amplifier; a second resistor connected to a first inverting input terminal of the first transconductance amplifier; the input circuit is used to convert an input voltage signal into a current signal and then output it; A load circuit is connected to the input circuit, and the load circuit includes: a second transconductance amplifier, wherein the non-inverting input terminal of the second transconductance amplifier is connected to the inverting output terminal of the first transconductance amplifier, and the inverting input terminal of the second transconductance amplifier is connected to the non-inverting output terminal of the first transconductance amplifier; a first filtering module, wherein one end is connected to the non-inverting input terminal of the second transconductance amplifier, and the other end is connected to the inverting output terminal of the second transconductance amplifier; a second filtering module, wherein one end is connected to the inverting input terminal of the second transconductance amplifier, and the other end is connected to the non-inverting output terminal of the second transconductance amplifier; the load circuit is used to receive the current signal, and convert the current signal into a voltage to generate a voltage signal; an adjustment circuit, connected to the load circuit, for adjusting the quality factor of the bandpass filter based on the voltage signal; A feedback circuit, wherein the input end of the feedback circuit is connected to the output end of the regulating circuit, and the output end of the feedback circuit is connected to the input end of the input circuit, and is used to feed back the low-frequency part of the output signal of the regulating circuit to the input circuit.

2. The filter according to claim 1, characterized in that The input circuit is a fully differential high-pass circuit.

3. The filter according to claim 1, characterized in that The load circuit is a fully differential low-pass circuit.

4. The filter according to claim 1, characterized in that The regulating circuit is a fully differential low-pass circuit.

5. The filter according to claim 1, characterized in that The regulating circuit comprises: a third transconductance amplifier, wherein a non-inverting input terminal of the third transconductance amplifier is connected to an inverting output terminal of the second transconductance amplifier, and an inverting input terminal of the third transconductance amplifier is connected to a non-inverting output terminal of the second transconductance amplifier; A first resistance-capacitance circuit, one end of which is connected to the non-inverting input end of the third transconductance amplifier, and the other end of which is connected to the inverting output end of the third transconductance amplifier; The second resistor-capacitor circuit has one end connected to the inverting input end of the third transconductance amplifier and the other end connected to the non-inverting output end of the third transconductance amplifier.

6. The filter according to claim 5, characterized in that The first resistance-capacitance circuit comprises: The third resistor; a fourth resistor, a first connection point of which after being connected in parallel with the third resistor is connected to the inverting output end of the third transconductance amplifier; a fifth resistor connected to a second connection point formed by connecting the third resistor and the fourth resistor; a third capacitor, one end of which is connected to the second connection point, the other end of which is connected to the non-inverting input terminal of the third transconductance amplifier, and is connected in parallel with the fifth resistor; A sixth resistor has one end connected to the fifth resistor and the other end connected to the non-inverting input terminal of the third transconductance amplifier.

7. The filter according to claim 6, characterized in that The second resistor-capacitor circuit has the same circuit structure as the first resistor-capacitor circuit.

8. The filter according to claim 5, characterized in that The feedback circuit comprises: A third resistance-capacitance circuit, one end of which is connected to the in-phase output end of the third transconductance amplifier, and the other end of which is connected to the second inverting input end of the first transconductance amplifier; A fourth resistor-capacitor circuit has one end connected to the inverting output end of the third transconductance amplifier, and the other end connected to the second non-inverting input end of the first transconductance amplifier.

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