Amplifier circuits and high-order damping circuits

Abstract

The present invention provides an amplifier circuit and a high-order damping circuit. The amplifier circuit includes an input stage amplifier, at least one intermediate stage amplifier and an output stage amplifier cascaded between an input port and an output port of the amplifier circuit. The amplifier circuit also includes a compensation capacitor coupled between the output port of the amplifier circuit and the output port of the input stage amplifier and a first high-order damping circuit coupled to the output port of the intermediate stage amplifier. The present invention can enhance the stability of a multi-stage amplifier while not reducing the in-band gain of the multi-stage amplifier.

Description

Technical Field

[0001] The present invention relates to amplifier design and, more particularly, to multi-stage amplifiers. Background Art

[0002] For many applications, the performance of a single-stage amplifier is usually not sufficient. Therefore, a multi-stage amplifier can be used by cascading several amplifier stages to achieve the desired performance. For example, in a three-stage amplifier, the output of the first-stage amplifier is used as the input of the second-stage amplifier, and the output of the second-stage amplifier is used as the input of the third-stage amplifier.

[0003] The stability of a multi-stage amplifier depends on the relative relationship between each non-dominant pole and the unity-gain frequency of the multi-stage amplifier. The frequency of the non-dominant pole should be higher than the unity-gain frequency, so that at each high-frequency non-dominant pole, the open-loop gain of the multi-stage amplifier is less than 1 (i.e., 0 dB). In this way, the multi-stage amplifier is stable in closed-loop operation. In order to solve the stability problem, some solutions have been proposed to move the non-dominant pole to a higher frequency. However, these solutions will result in a decrease in in-band gain.

[0004] Therefore, there is a need for an innovative frequency compensation design that can enhance the stability of a multi-stage amplifier without reducing the in-band gain of the multi-stage amplifier. Summary of the invention

[0005] One of the objectives of the present invention is to provide a multi-stage amplifier with a high-order damping circuit to solve the above-mentioned problem.

[0006] An amplifier circuit according to an exemplary embodiment of the present invention comprises an input stage amplifier, at least one intermediate stage amplifier and an output stage amplifier cascaded between an input port and an output port of the amplifier circuit. The amplifier circuit further comprises a compensation capacitor coupled between the output port of the amplifier circuit and the output port of the input stage amplifier and a first high-order damping circuit coupled to the output port of the intermediate stage amplifier.

[0007] In an exemplary embodiment, the amplifier circuit further has a second high-order damping circuit coupled to the output port of the input stage amplifier.

[0008] The high-order damping circuit according to an exemplary embodiment has a first-stage high-pass filter, a second-stage high-pass filter and an auxiliary amplifier. The input port of the first-stage high-pass filter is coupled to the output port of the input stage amplifier or the output port of the intermediate stage amplifier. The input port of the second-stage high-pass filter is coupled to the output port of the first-stage high-pass filter. The input port of the auxiliary amplifier is coupled to the output port of the second-stage high-pass filter, and its output port is coupled to the input port of the first-stage high-pass filter.

[0009] According to the amplifier circuit and the high-order damping circuit of the present invention, the stability of the multi-stage amplifier can be enhanced while the in-band gain of the multi-stage amplifier is not reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The accompanying drawings illustrate embodiments of the present invention and together with the description serve to explain the principles of the present invention. In the accompanying drawings:

[0011] Figure 1 is a schematic diagram illustrating an amplifier circuit according to an exemplary embodiment of the present invention.

[0012] Figure 2 is a graph of the output equivalent resistance Rout2 versus the frequency w, which illustrates the concept of the frequency compensation solution (implemented by a high-order damping circuit) proposed according to an exemplary embodiment of the present invention.

[0013] Figure 3A and Figure 3B Two second order damping circuits according to an exemplary embodiment of the present invention are shown.

[0014] Figure 4A A second-order damping circuit according to another exemplary embodiment of the present invention is shown, which uses an operational transconductance amplifier to implement a transconductance of G d Auxiliary amplifier.

[0015] Figure 4B A second-order damping circuit according to another exemplary embodiment of the present invention is shown, which uses an output rail-to-rail OTA to achieve a transconductance of G d Auxiliary amplifier.

[0016] Figure 5 A second-order damping circuit according to another exemplary embodiment is shown, which uses a current mode high-pass filter to implement a second-order high-pass filter and provides a transconductance G. d .

[0017] Fig. 6A A third order damping circuit is shown.

[0018] Figure 6BAnother third order damping circuit is shown.

[0019] Figure 7 An amplifier circuit according to another exemplary embodiment of the present invention is shown.

[0020] Figure 8 An amplifier circuit according to another exemplary embodiment of the present invention is shown. DETAILED DESCRIPTION

[0021] Certain words are used in the specification and claims to refer to specific components. It should be understood by those skilled in the art that electronic equipment manufacturers may use different terms to refer to the same component. The specification and claims do not distinguish components by differences in name, but by differences in the functions of the components. The term "including" mentioned throughout the specification and claims is an open-ended term and should be interpreted as "including but not limited to". In addition, the term "coupled" is used herein to include any direct and indirect electrical connection means. Therefore, if the text describes a first device as being electrically connected to a second device, it means that the first device can be directly connected to the second device, or indirectly connected to the second device through other devices or connection means.

[0022] Figure 1 1 is a schematic diagram showing an amplifier circuit 100 according to an exemplary embodiment of the present invention. By way of example and not limitation, the amplifier circuit 100 may be used in audio applications. Figure 1 As shown, the amplifier circuit 100 includes a multi-stage amplifier (for example, a three-stage amplifier may include a cascaded amplifier connected at an input port (V IN ) and output port (V OUT ), an input-stage amplifier 102_1, at least one intermediate-stage amplifier 102_2 and an output-stage amplifier 102_3, a high-order damping circuit 104, and a plurality of compensation capacitors (e.g., C m1 and C m2 ). The amplifier circuit 100 also has a load capacitor C at the output port. L and resistor R Z .

[0023] The transconductance of amplifiers 102_1, 102_2 and 102_3 is respectively determined by G m1 , G m2 and G m3 The amplifier circuit 100 uses an input stage amplifier 102_1 to receive an input voltage VIN , and uses the output stage amplifier 102_3 to output the output voltage V OUT . Compensation capacitor C m1 and C m2 are used for Miller compensation. Therefore, the compensation capacitor C m1 and C m2 To implement a nested Miller compensation (NMC) scheme. However, this is for illustrative purposes only and is not meant to be limiting of the present invention. In some embodiments of the present invention, according to design considerations, the compensation capacitor C m2 Can be optional. Compensation capacitor C m1 coupled to the output port (V OUT ) between the output port P1 of the input stage amplifier 102_1. The optional compensation capacitor C m2 coupled to the output port (V OUT ) and the output port P2 of the intermediate stage amplifier 102_2.

[0024] In this exemplary embodiment, the high-order damping circuit 104 is also a compensation design. The high-order damping circuit 104 is coupled to the output port P2 of the intermediate stage amplifier 102_2 and includes a capacitor C d , resistor R B , high pass filter 106 and auxiliary amplifier 108 (whose transconductance is G d ). Capacitor C d The connection terminal 110 is coupled to the resistor R B (Resistor R B One end is coupled to the reference voltage source V B / GND) to form a first-stage high-pass filter, the input port 112 of the first-stage high-pass filter is coupled to the output port P2 of the intermediate stage amplifier 102_2, and the output port (referring to the connection end 110) of the first-stage high-pass filter is coupled to the input port of the high-pass filter 106. The high-pass filter 106 that performs the second-stage high-pass filtering function can be named as a second-stage high-pass filter. The input port of the auxiliary amplifier 108 is coupled to the output port of the second-stage high-pass filter 106, and the output port of the auxiliary amplifier 108 is coupled to the input port 112 of the first-stage high-pass filter. As shown in the figure, the first-stage high-pass filter (C d and R B ), the second stage high pass filter 106 and the auxiliary amplifier 108 form a loop. The second stage high pass filter 106 can be a first order high pass filter (for example, another pair of resistors and capacitors (in the following figures, R F and C FThe damping circuit 104 may be a second-order damping circuit or an N-order damping circuit, where N is greater than 2.

[0025] The high-order damping circuit 104 introduces a topology called damping-factor-control frequency compensation (DFCFC) for the multi-stage amplifier, which can significantly increase the bandwidth and improve the transient response.

[0026] Figure 2 1 is a graph of output equivalent resistance Rout2 versus frequency w, which illustrates the concept of the frequency compensation scheme (implemented by the high-order damping circuit 104) proposed according to an exemplary embodiment of the present invention. The output equivalent resistance Rout2 is the resistance measured by looking back at the intermediate stage amplifier 102_2. Figure 2 It is shown that by the high-order damping circuit 104, the non-dominant pole is pushed to a frequency higher than the unity gain frequency f_UGB (e.g., about 1 MHz) and the stability of the amplifier circuit 100 is guaranteed. At the same time, compared with the conventional first-order damping circuit, there is no need to reduce the equivalent resistance Rout2 in the audio frequency band (e.g., 20 Hz to 20 KHz). Therefore, in the audio frequency band, the gain of the intermediate stage amplifier 102_2 is not reduced. The problem of gain reduction within the band is solved. The large gain of the intermediate stage amplifier 102_2 successfully suppresses the crossover distortion of the output stage. The inner loop gain of the amplifier circuit 100 is maintained.

[0027] Compared with the first-order damping circuit, the high-order damping circuit 104 can rapidly reduce the output equivalent resistance Rout2 within the expected frequency range. In the audio frequency band (eg, 20 Hz to 20 KHz), the output equivalent resistance Rout2 will not decrease.

[0028] In short, the amplifier circuit 100 with the proposed frequency compensation implemented by the high-order damping circuit 104 can maintain stability without reducing the in-band gain.

[0029] There are many ways to implement the high-order damping circuit 104 . Figure 3A and Figure 3B Two second-order damping circuits 302 and 304 according to an exemplary embodiment of the present invention are shown. Based on a current mirror structure, the auxiliary amplifier 108 is implemented using transistors (e.g., metal oxide semiconductor field effect transistors MOSFET) to provide a transconductance G d The MOSFET (306 / 308) has a gate and a drain which serve as an input port and an output port of the auxiliary amplifier 108, respectively. Figure 3AThe second order damping circuit 302 in is of NMOS design. Figure 3B The second-order damping circuit 304 is a PMOS design. B and C d In addition to the resistor-capacitor high-pass filter formed, the second-stage high-pass filter (HPF) 310 / 312 also provides a resistor R F and capacitor C F , to form another resistor-capacitor high-pass filter in the circuit loop. B and C d The connection between the terminals is through a capacitor C F Coupled to the gate of MOSFET 306 / 308, resistor R F Coupled between the gates of MOSFETs 306 / 308 and a reference voltage source VB.

[0030] Figure 4A A second-order damping circuit 402 according to another exemplary embodiment of the present invention is shown, which uses an operational transconductance amplifier (OTA) 404 to achieve a transconductance of G d Auxiliary amplifier 108. OTA 404 (including transconductance G d1 and G d2 The two transistors of the auxiliary amplifier 108 have a first differential input terminal 406 as an input port of the auxiliary amplifier 108, a second differential input terminal 408 coupled to a reference voltage source VB, and an output terminal 410 as an output port of the auxiliary amplifier 108. Figure 4A The auxiliary amplifier 108 may be implemented with any other operational transconductance amplifier structure other than the structure shown.

[0031] Figure 4B A second-order damping circuit 412 according to another exemplary embodiment of the present invention is shown, which uses an output rail-to-rail OTA 414 to achieve a transconductance of G. d The output rail-to-rail OTA 414 has a first differential input terminal 416 as an input port of the auxiliary amplifier 108, a second differential input terminal 418 coupled to the reference voltage source VB, and an output terminal 420 as an output port of the auxiliary amplifier 108. It should be noted that the use of MOSFET (306 / 308), OTA 404, or output rail-to-rail OTA 414 to implement the auxiliary amplifier 108 is only an example, and any amplifier that can implement the transconductance Gd can be used in the present application to implement the auxiliary amplifier 108.

[0032] Figure 5A second-order damping circuit 500 according to another exemplary embodiment is shown, which uses a current mode high-pass filter 502 to implement the second-stage high-pass filter 106 and provide a transconductance G d (by transconductance G d1 and G d2 The first stage high-pass filtering is done by capacitor C d , resistor R B1 and resistor R B2 Implementation. Any current mode high pass filter structure known in the art can be used for implementation.

[0033] It should be noted that the implementation of the second-stage high-pass filter 106 shown in this document is only an example, and the second-stage high-pass filter 106 can also be implemented using any high-pass filter known in the art.

[0034] The high-order damping circuit 104 of the present invention is not limited to a second-order design. Fig. 6A A second-order high-pass filter 602 (with capacitor C F1 and resistor R F1 and capacitor C F2 and resistor R F2 Composition) instead Figure 3A A first-order RC high-pass filter 310, Fig. 6A A third order damping circuit 604 is shown. Figure 6B Another third order damping circuit 606 is shown, Figure 5 The current mode high pass filter 502 (first order circuit) is replaced by the second order current mode high pass filter 608 (including capacitor C F1 and resistor R F1 and capacitor C F2 and resistor R F2 )replace.

[0035] The high-order damping circuit 104 is not limited to being coupled to the output port P2 of the intermediate-stage amplifier 102_2 . Figure 7 An amplifier circuit 700 according to another exemplary embodiment of the present invention is shown, which has a high-order damping circuit 702 (implemented by any of the high-order damping circuits described above) coupled to the output port P1 of the input stage amplifier 102_1 .

[0036] The multi-stage amplifier used in the amplifier circuit 100 / 700 is a three-stage amplifier. However, the same frequency compensation scheme (moving the non-dominant pole to a higher frequency by a high-order damping circuit) can be extended and applied to a multi-stage amplifier having more than three amplifier stages. Figure 88 is a schematic diagram showing an amplifier circuit 800 according to another exemplary embodiment of the present invention. By way of example and not limitation, the amplifier circuit 800 may be used in audio applications. The amplifier circuit 800 is a multi-stage amplifier circuit including amplifiers AMP1 to AMP N , (N-1) high-order damping circuits HODC1 to HODC(N-1) and (N-1) compensation capacitors C m1 ~C m(N-1) The N-stage amplifier is constructed, where N is a positive integer greater than 3 (ie, N>3). The compensation capacitor C m1 ~C m(N-1) Regarding the proposed frequency compensation scheme (moving the non-dominant pole to a higher frequency through a high-order damping circuit), the compensation capacitor C m2 ~C m(N-1) In other words, in some embodiments of the present invention, the compensation capacitor C may be omitted according to design considerations. m2 ~C m(N-1) According to design considerations, the high-order damping circuits HODC1-HODC(N-1) can be implemented using one of the aforementioned damping circuits. According to the proposed frequency compensation scheme, the non-dominant poles are controlled by the high-order damping circuits HODC1-HODC(N-1) to avoid in-band degradation. In this way, the amplifier circuit 800 can be stable without reducing the in-band gain.

[0037] Although the present invention has been described by way of example and according to preferred embodiments, it should be understood that the present invention is not limited to the disclosed embodiments. On the contrary, it will be apparent to one of ordinary skill in the art that the present invention is intended to encompass various modifications and similar arrangements. Therefore, the scope of the appended claims should be given the broadest interpretation to encompass all such modifications and similar arrangements.

Claims

1. An amplifier circuit, comprising: an input stage amplifier, at least one intermediate stage amplifier, and an output stage amplifier cascaded between the input port and the output port of the amplifier circuit; a compensation capacitor coupled between an output port of the amplifier circuit and an output port of the input stage amplifier; as well as A first high-order damping circuit coupled to an output port of the input stage amplifier or an output port of the intermediate stage amplifier; Wherein, the first high-order damping circuit comprises: A first stage high pass filter, an input port of which is coupled to the intermediate stage amplifier; A second-stage high-pass filter, whose input port is coupled to the output port of the first-stage high-pass filter; and The auxiliary amplifier has an input port coupled to the output port of the second-stage high-pass filter and an output port coupled to the input port of the first-stage high-pass filter.

2. The amplifier circuit according to claim 1, characterized in that The first-stage high-pass filter is a first resistor-capacitor high-pass filter, wherein a first capacitor is coupled between an input port and a connection terminal of the first-stage high-pass filter, and a first resistor is coupled between the connection terminal and a reference voltage source; as well as The second-stage high-pass filter is a second resistor-capacitor high-pass filter, wherein a second capacitor is coupled between the connection terminal and the input port of the auxiliary amplifier, and a second resistor is coupled between the input port of the auxiliary amplifier and the reference voltage source.

3. The amplifier circuit according to claim 1, characterized in that The auxiliary amplifier includes a transistor, a gate and a drain of the transistor are respectively an input port and an output port of the auxiliary amplifier.

4. The amplifier circuit according to claim 1, characterized in that The auxiliary amplifier is an operational transconductance amplifier having a first differential input terminal as an input port of the auxiliary amplifier, a second differential input terminal coupled to a reference voltage source, and an output terminal as an output port of the auxiliary amplifier.

5. The amplifier circuit according to claim 1, characterized in that The auxiliary amplifier is an output rail-to-rail operational transconductance amplifier having a first differential input terminal as an input port of the auxiliary amplifier, a second differential input terminal coupled to a reference voltage source, and an output terminal as an output port of the auxiliary amplifier.

6. The amplifier circuit according to claim 1, characterized in that The second stage high pass filter is implemented by a current mode high pass filter.

7. The amplifier circuit according to claim 1, characterized in that The second-stage high-pass filter is a high-order high-pass filter.

8. The amplifier circuit according to claim 1, characterized in that The amplifier circuit further includes a second high-order damping circuit, wherein the first high-order damping circuit is coupled to an output port of the intermediate stage amplifier, and the second high-order damping circuit is coupled to an output port of the input stage amplifier.

9. The amplifier circuit according to claim 8, characterized in that The second high-order damping circuit comprises: A third-stage high-pass filter, whose input port is coupled to the output port of the input-stage amplifier; a fourth-stage high-pass filter, whose input port is coupled to the output port of the third-stage high-pass filter; and Another auxiliary amplifier has an input port coupled to the output port of the fourth-stage high-pass filter, and an output port coupled to the input port of the third-stage high-pass filter.

10. A high-order damping circuit for compensating for in-band gain attenuation of an amplifier circuit, the amplifier circuit comprising an input stage amplifier, at least one intermediate stage amplifier and an output stage amplifier cascaded between an input port and an output port of the amplifier circuit, the high-order damping circuit comprising: A first stage high pass filter, an input port of which is coupled to the output port of the input stage amplifier or the output port of the intermediate stage amplifier; A second-stage high-pass filter, whose input port is coupled to the output port of the first-stage high-pass filter; as well as The auxiliary amplifier has an input port coupled to the output port of the second-stage high-pass filter and an output port coupled to the input port of the first-stage high-pass filter.

11. The high-order damping circuit according to claim 10, characterized in that: The first-stage high-pass filter is a first resistor-capacitor high-pass filter, wherein a first capacitor is coupled between an input port and a connection terminal of the first-stage high-pass filter, and a first resistor is coupled between the connection terminal and a reference voltage source; as well as The second-stage high-pass filter is a second resistor-capacitor high-pass filter, wherein a second capacitor is coupled between the connection terminal and the input port of the auxiliary amplifier, and a second resistor is coupled between the input port of the auxiliary amplifier and the reference voltage source.

12. The high-order damping circuit according to claim 10, characterized in that: The auxiliary amplifier includes a transistor, a gate and a drain of the transistor are respectively an input port and an output port of the auxiliary amplifier.

13. The high-order damping circuit according to claim 10, characterized in that: The auxiliary amplifier is an operational transconductance amplifier having a first differential input terminal as an input port of the auxiliary amplifier, a second differential input terminal coupled to a reference voltage source, and an output terminal as an output port of the auxiliary amplifier.

14. The high-order damping circuit according to claim 10, characterized in that: The auxiliary amplifier is an output rail-to-rail operational transconductance amplifier having a first differential input terminal as an input port of the auxiliary amplifier, a second differential input terminal coupled to a reference voltage source, and an output terminal as an output port of the auxiliary amplifier.

15. The high-order damping circuit according to claim 10, characterized in that: The second stage high pass filter is implemented by a current mode high pass filter.

16. The high-order damping circuit according to claim 10, characterized in that: The second-stage high-pass filter is a high-order high-pass filter.

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