Microphone amplifier circuit design method and microphone amplifier circuit

Abstract

The present invention provides a method for designing a microphone amplifier circuit. The method includes: providing a layer of underlayer metal between a substrate and a pad of an integrated circuit, forming a first parasitic capacitance between the pad and the underlayer metal, and forming a second parasitic capacitance between the underlayer metal and the substrate; searching for a circuit point in an amplifier circuit and making the circuit point meet a predetermined condition; connecting the underlayer metal to the circuit point and connecting the pad to an input end; welding a microphone to the pad of the integrated circuit to function as a microphone capacitance, connecting one end of the microphone capacitance to a high-voltage bias voltage and the other end to an input end, connecting one end of the first parasitic capacitance to an input end, connecting the other end to an output end, connecting one end of the second parasitic capacitance to an output end, and grounding the other end. The present invention also provides a microphone amplifier circuit. Compared with the related art, the design method of the microphone amplifier circuit and the microphone amplifier circuit of the present invention have a higher signal-to-noise ratio and better performance.

Description

[Technical field]

[0001] The present invention relates to the field of microphone amplifier circuits, and more particularly to a microphone amplifier circuit and a method for designing the same that eliminates the effect of pad parasitic capacitance on the signal-to-noise ratio. [Background technology]

[0002] With the development of mobile communication technology, mobile terminals such as mobile phones, PADs, and notebook computers have gradually become indispensable electronic products in our lives. In these electronic products, the signal-to-noise ratio when the signal picked up by the built-in microphone as a voice pickup unit and output through the microphone amplifier circuit is an important evaluation index of the product performance.

[0003] In the microphone amplifier circuit of the related art, as shown in FIG. 1, the microphone is welded to the microphone amplifier circuit of the integrated circuit by a pad, and a pad parasitic capacitance C PAD ' is formed, and the pad parasitic capacitance C PAD ' and the microphone capacitance C of the microphone Mic The amplifier M1' constitutes a capacitance series circuit and reduces the signal amplitude at the input terminal Vin' by voltage division. The amplifier M1' has circuit noise and a pad parasitic capacitance C PAD The input signal becomes smaller due to the voltage division of ', so the output terminal V Out In particular, the signal-to-noise ratio at the microphone capacitance C Mic When ' is small, the voltage division is more significant and the degradation of the signal-to-noise ratio is more significant, so the performance of the microphone amplifier circuit is poor.

[0004] Therefore, in order to solve the above technical problems, it is necessary to provide a new microphone amplifier circuit design method and microphone amplifier circuit. Summary of the Invention [Problem to be solved by the invention]

[0005] The technical problem to be solved by the present invention is to provide a method for designing a microphone amplifier circuit having a high signal-to-noise ratio, and a microphone amplifier circuit. [Means for solving the problem]

[0006] In order to solve the above technical problems, the present invention provides a design method for a microphone amplifier circuit, the design method being applied to a microphone and an amplifier circuit, the amplifier circuit including an amplifier, a bias resistor, an input terminal and an output terminal, the input of the amplifier is connected to the input terminal and is connected in series with the bias resistor and then connected to a bias voltage, the output of the amplifier is connected to the output terminal, the method includes: providing a layer of underlying metal between a substrate and a pad of an integrated circuit, isolating the pad, the underlying metal, and the substrate by spacing them from one another, and forming a first parasitic capacitance between the pad and the underlying metal, and a second parasitic capacitance between the underlying metal and the substrate; searching for a circuit point in the amplifier circuit, and making the circuit point satisfy condition A that the circuit point is in phase with the input terminal, condition B that the voltage gain of the circuit point with respect to the input terminal is 0.8 or more, and condition C that the circuit point is within a signal path from the input terminal to the output terminal; connecting said metallization to said circuit point and said pad to said input; and welding the microphone to a pad of an integrated circuit so that the microphone is connected to the pad and functions as a microphone capacitance, and connecting one end of the microphone capacitance to a high-voltage bias voltage, connecting the other end of the microphone capacitance to the input end, connecting one end of the first parasitic capacitance to the input end, connecting the other end of the first parasitic capacitance to the output end, connecting one end of the second parasitic capacitance to the output end, and grounding the other end of the second parasitic capacitance.

[0007] Preferably, said circuit point is said output terminal.

[0008] Preferably, the amplifier is a transistor, the gate of the transistor being the input terminal, the source of the transistor being the output terminal, and the drain of the transistor being connected to ground.

[0009] Preferably, the amplifier circuit further includes a constant current source, one end of which is connected to a power supply voltage and the other end of which is connected to a source of the transistor and supplies a bias current to the transistor.

[0010] Preferably, the microphone capacitance is a variable capacitance.

[0011] The present invention provides a microphone amplifier circuit, the microphone amplifier circuit including: an amplifier, a bias resistor, an input end, an output end, a microphone capacitance, a first parasitic capacitance and a second parasitic capacitance; an input of the amplifier is connected to the input terminal and an output of the amplifier is connected to the output terminal; one end of the bias resistor is connected to a bias voltage, and the other end of the bias resistor is connected to the input terminal; One end of the microphone capacitance is connected to a high-voltage bias voltage, and the other end of the microphone capacitance is connected to the input terminal; one end of the first parasitic capacitance is connected to the input terminal, the other end of the first parasitic capacitance is connected to the output terminal, one end of the second parasitic capacitance is connected to the output terminal, and the other end of the second parasitic capacitance is grounded; The first parasitic capacitance and the second parasitic capacitance are formed by adding a layer of underlying metal between a substrate of an integrated circuit and the pad, the pad and the underlying metal are spaced apart from each other to form the first parasitic capacitance, and the pad is connected to the input terminal, the underlying metal and the substrate are spaced apart from each other to form the second parasitic capacitance, and the underlying metal is connected to the output terminal.

[0012] Preferably, the amplifier is a transistor, the gate of the transistor being the input terminal, the source of the transistor being the output terminal, and the drain of the transistor being connected to ground.

[0013] Preferably, the amplifier circuit further includes a constant current source, one end of which is connected to a power supply voltage and the other end of which is connected to a source of the transistor and supplies a bias current to the transistor.

[0014] Preferably, the microphone capacitance is a variable capacitance.

[0015] Preferably, the microphone amplifier circuit is designed and formed by the microphone amplifier circuit design method according to the present invention. Effect of the Invention

[0016] Compared with the related art, in the microphone amplifier circuit design method and microphone amplifier circuit of the present invention, a layer of underlying metal is provided between the pad of the integrated circuit and the substrate to shield the pad capacitance, thereby forming new first and second parasitic capacitances; by searching for a circuit point in the amplifier circuit that satisfies a condition, the underlying metal is connected to the circuit point, so that the signals at both ends of the first parasitic capacitance are in phase and the gain is equal to or greater than 0.8, the capacitance has no or small charge change, the microphone has no or small loading effect on the input end, so as not to cause a reduction in the input signal due to voltage division; and the second parasitic capacitance, as a load on the output end, has a sufficiently large driving capability of the output end and does not affect the signal-to-noise ratio at the output end, thereby greatly reducing and even eliminating the influence of the parasitic capacitance of the pad on the signal-to-noise ratio of the microphone amplifier circuit, and effectively improving the circuit performance.

[0017] In order to more clearly describe the technical solutions in the embodiments of the present invention, the following briefly introduces drawings necessary for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention, and those skilled in the art can further obtain other drawings based on these drawings without any creative work. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a circuit diagram of a microphone amplifier circuit in the related art. [Diagram 2] 2 is a flowchart of a method for designing a microphone amplifier circuit according to the present invention. [Diagram 3] 1 is a circuit diagram of a microphone amplifier circuit according to the present invention; [Figure 4] 1 is a circuit diagram of a microphone amplifier circuit according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The following clearly and completely describes the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments that a person skilled in the art can obtain without creative labor are all included in the protection scope of the present invention.

[0020] At the same time, as shown in Figures 2-3, the present invention provides a design method for a microphone amplifier circuit, which is applied to a microphone and an amplifier circuit. The amplifier circuit includes an amplifier Amp, a bias resistor R B , input terminal V in and output terminal V out The input of the amplifier Amp is connected to the input terminal V in and the bias resistor R B and then connected in series with the bias voltage V B and the output of the amplifier Amp is connected to the output terminal V out The method includes the following steps S1 to S4.

[0021] In step S1, a layer of an underlying metal M1 is provided between a substrate P-sub of an integrated circuit and a pad MT, and the pad MT, the underlying metal M1, and the substrate P-sub are insulated from each other by two layers at intervals, and a first parasitic capacitance C is provided between the pad MT and the underlying metal M1. PAD1 and a second parasitic capacitance C PAD2 Form.

[0022] The provision of the underlayer metal M1 is used to shield the pad capacitance of the pad MT, thereby creating a new first parasitic capacitance C PAD1 and the second parasitic capacitance C PAD2 Form.

[0023] In step S2, a circuit point X is found in the amplifier circuit, and the circuit point X is made to satisfy the following conditions A to C. Condition A: The circuit point X is connected to the input terminal V in is in phase with Condition B: The input terminal V of the circuit point X in is 0.8 or more, and preferably 1. Of course, the gain here can be closer to 1, such as 0.9 or 0.8. Condition C: The circuit point X is connected to the input terminal V of the amplifier circuit. in to the output terminal V out It is located within the signal corridor.

[0024] When the above three conditions are simultaneously satisfied, a decision point X is found in the amplifier circuit. In this embodiment, the decision point X is located at the output terminal V out and the output terminal V out satisfies the above three conditions.

[0025] In step S3, the base metal M1 is connected to the circuit point X, and the pad MT is connected to the input terminal V in Connect to.

[0026] In step S4, the microphone is welded to a pad MT of the integrated circuit so that the microphone is connected, and the microphone capacitance C Mic and the microphone capacitance C Mic One end of the CP and the microphone capacitance C Mic The other end of the input terminal V in and the first parasitic capacitance C PAD1 One end of the input terminal V in and the first parasitic capacitance C PAD1 The other end of the output terminal V out and the second parasitic capacitance C PAD2 One end of the output terminal V out and the second parasitic capacitance C PAD2 The other end is grounded.

[0027] In this embodiment, the microphone capacitance C Mic is a variable capacitance.

[0028] Preferably, as shown in FIG. 4, the present invention further provides another embodiment, that is, in addition to the embodiment of FIG. 3, the amplifier Amp is a transistor M. The gate of the transistor M is connected to the input terminal V in or the gate of the transistor M is connected to the input terminal V in The source of the transistor M is connected to the output terminal V out or the source of the transistor M is connected to the output terminal V out The drain of the transistor M is connected to ground.

[0029] Preferably, the amplifier circuit further includes a constant current source I, one end of the constant current source I is connected to a power supply voltage VDD, the other end of the constant current source I is connected to the source of the transistor M, and a bias current I B supplies.

[0030] In the microphone amplifier circuit designed by the above method of the present invention, the first parasitic capacitance C PAD1 is the first parasitic capacitance CPAD1 Since the signals at both ends of are in phase and the gain is 1, the first parasitic capacitance C PAD1 There is no charge change at the input terminal V in There is no loading effect on the input terminal V in The second parasitic capacitance C PAD2 is the output terminal V out The load is V out The driving capability of the output terminal V out In order to avoid affecting the signal-to-noise ratio in the microphone amplifier circuit, the pad parasitic capacitance in the pad for welding the conventional microphone is shielded by installing the underlying metal M1, and new first and second parasitic capacitances are formed, thereby effectively reducing and even eliminating the effect of the original pad parasitic capacitance on the signal-to-noise ratio, and further effectively adjusting the signal-to-noise ratio of the microphone amplifier circuit and improving the circuit performance.

[0031] As shown in FIG. 3, the embodiment of the present invention further provides a microphone amplifier circuit 100, which includes an amplifier Amp, a bias resistor R B , input terminal V in and output terminal V out , microphone capacitance C Mic , the first parasitic capacitance C PAD1 and the second parasitic capacitance C PAD2 Includes.

[0032] The input of the amplifier Amp is connected to the input terminal V in and the output of the amplifier Amp is connected to the output terminal V out is connected to

[0033] The bias resistor R B One end of the bias voltage V B and the bias resistor R B The other end of the input terminal V in is connected to

[0034] The microphone capacitance C Mic One end of the CPand the microphone capacitance C Mic The other end of the input terminal V in In this embodiment, the microphone capacitance C Mic is a variable capacitance.

[0035] The first parasitic capacitance C PAD1 One end of the input terminal V in and the first parasitic capacitance C PAD1 The other end of the output terminal V out and the second parasitic capacitance C PAD2 One end of the output terminal V out and the second parasitic capacitance C PAD2 The other end is grounded.

[0036] Here, in the microphone amplifier circuit 100, specifically, the microphone capacitance C Mic The first parasitic capacitance C PAD1 and the second parasitic capacitance C PAD2 is formed by adding one layer of underlying metal M1 between the substrate P-sub of the integrated circuit and the pad MT, and the first parasitic capacitance C PAD1 is formed and the pad MT is connected to the input terminal V in , and the second parasitic capacitance C PAD2 is formed and the base metal M1 is connected to the output terminal V out is connected to

[0037] Specifically, as shown in FIG. 4, the microphone amplifier circuit 100 further provides a specific embodiment, that is, the Amp is a transistor M, and the gate of the transistor M is connected to the input terminal V in or the gate of the transistor M is connected to the input terminal V in , and the source of the transistor M is connected to the output terminal V out or the source of the transistor M is connected to the output terminal V outand the drain of the transistor M is connected to ground.

[0038] In the microphone amplifier circuit 100 of the present invention, the first parasitic capacitance C PAD1 is the first parasitic capacitance C PAD1 Since the signals at both ends of are in phase and the gain is 1, the first parasitic capacitance C PAD1 There is no charge change at the input terminal V in There is no loading effect on the input terminal V in The second parasitic capacitance C PAD2 is the output terminal V out The load is V out The driving capability of the output terminal V out In order to avoid affecting the signal-to-noise ratio in the microphone amplifier circuit, the pad parasitic capacitance in the pad for welding the conventional microphone is shielded by installing the underlying metal M1, and new first and second parasitic capacitances are formed, thereby effectively reducing and even eliminating the effect of the original pad parasitic capacitance on the signal-to-noise ratio, and further effectively adjusting the signal-to-noise ratio of the microphone amplifier circuit and improving the circuit performance.

[0039] Preferably, the amplifier circuit further includes a constant current source I, one end of the constant current source I is connected to a power supply voltage VDD, the other end of the constant current source I is connected to the source of the transistor M, and a bias current I B supplies.

[0040] It should be noted that the microphone amplifier circuit of the present invention is designed and formed by the above-mentioned microphone amplifier circuit design method according to the present invention.

[0041] Compared with the related art, in the microphone amplifier circuit design method and microphone amplifier circuit of the present invention, a layer of underlying metal is provided between the pad of the integrated circuit and the substrate to shield the pad capacitance, thereby forming new first and second parasitic capacitances; by searching for a circuit point in the amplifier circuit that satisfies a condition, the underlying metal is connected to the circuit point, so that the signals at both ends of the first parasitic capacitance are in phase and the gain is equal to or greater than 0.8, the capacitance has no or small charge change, the microphone has no or small loading effect on the input end, so as not to cause a reduction in the input signal due to voltage division; and the second parasitic capacitance, as a load on the output end, has a sufficiently large driving capability of the output end and does not affect the signal-to-noise ratio at the output end, thereby greatly reducing and even eliminating the influence of the parasitic capacitance of the pad on the signal-to-noise ratio of the microphone amplifier circuit, and effectively improving the circuit performance.

[0042] The above are only examples of the present invention and are not intended to limit the scope of the patent of the present invention. Any equivalent structure or equivalent flow transformation made by utilizing the contents of the specification and drawings of the present invention, or any direct or indirect application to other related technical fields, are also included in the scope of patent protection of the present invention.

Claims

1. A method for designing a microphone amplifier circuit, which is applied to a microphone and an amplifier circuit, comprising the steps of: The amplifier circuit includes an amplifier, a bias resistor, an input terminal and an output terminal, the input of the amplifier is connected to the input terminal and is connected in series with the bias resistor and then connected to a bias voltage, and the output of the amplifier is connected to the output terminal; The design method includes: providing a layer of underlying metal between a substrate and a pad of an integrated circuit, isolating the pad, the underlying metal, and the substrate by spacing them from one another, and forming a first parasitic capacitance between the pad and the underlying metal, and a second parasitic capacitance between the underlying metal and the substrate; a step of searching for a circuit point in the amplifier circuit, and making the circuit point satisfy a condition A that the voltage of the circuit point and the voltage of the input terminal are in phase with each other, a condition B that the voltage gain of the circuit point with respect to the input terminal is 0.8 or more and 1 or less, and a condition C that the circuit point is the output terminal; connecting said metallization to said circuit point and said pad to said input; a step of welding the microphone to a pad of an integrated circuit so as to connect the microphone, causing the microphone to function as a microphone capacitance, and connecting one end of the microphone capacitance to a high bias voltage, connecting the other end of the microphone capacitance to the input end, connecting one end of the first parasitic capacitance to the input end via the pad, connecting the other end of the first parasitic capacitance to the output end via the underlying metal, connecting one end of the second parasitic capacitance to the output end via the underlying metal, and grounding the other end of the second parasitic capacitance by grounding the substrate.

2. A method for designing a microphone amplifier circuit, which is applied to a microphone and an amplifier circuit, comprising the steps of: the amplifier circuit includes a transistor, a bias resistor, an input terminal, and an output terminal, the gate of the transistor being the input terminal and being connected in series with the bias resistor and then connected to a bias voltage, the source of the transistor being the output terminal, and the drain of the transistor being connected to ground; The design method includes: providing a layer of underlying metal between a substrate and a pad of an integrated circuit, isolating the pad, the underlying metal, and the substrate by spacing them from one another, and forming a first parasitic capacitance between the pad and the underlying metal, and a second parasitic capacitance between the underlying metal and the substrate; a step of searching for a circuit point in the amplifier circuit, and making the circuit point satisfy a condition A that the voltage of the circuit point and the voltage of the input terminal are in phase with each other, a condition B that the voltage gain of the circuit point with respect to the input terminal is 0.8 or more and 1 or less, and a condition C that the circuit point is the output terminal; connecting said metallization to said circuit point and said pad to said input; a step of welding the microphone to a pad of an integrated circuit so as to connect the microphone, causing the microphone to function as a microphone capacitance, and connecting one end of the microphone capacitance to a high bias voltage, connecting the other end of the microphone capacitance to the input end, connecting one end of the first parasitic capacitance to the input end via the pad, connecting the other end of the first parasitic capacitance to the output end via the underlying metal, connecting one end of the second parasitic capacitance to the output end via the underlying metal, and grounding the other end of the second parasitic capacitance by grounding the substrate.

3. 3. The microphone amplifier circuit design method according to claim 2, wherein the amplifier circuit further includes a constant current source, one end of the constant current source being connected to a power supply voltage and the other end of the constant current source being connected to a source of the transistor and supplying a bias current to the transistor.

4. 3. The method for designing a microphone amplifier circuit according to claim 1, wherein the microphone capacitance is a variable capacitance.

5. 1. A microphone amplifier circuit, comprising: The amplifier includes a bias resistor, an input terminal, an output terminal, a microphone capacitance, a first parasitic capacitance, and a second parasitic capacitance; an input of the amplifier is connected to the input terminal and an output of the amplifier is connected to the output terminal; one end of the bias resistor is connected to a bias voltage, and the other end of the bias resistor is connected to the input terminal; One end of the microphone capacitance is connected to a high bias voltage, and the other end of the microphone capacitance is connected to the input end; one end of the first parasitic capacitance is connected to the input terminal via a pad, the other end of the first parasitic capacitance is connected to the output terminal via an underlying metal, and one end of the second parasitic capacitance is connected to the output terminal via the underlying metal; the first parasitic capacitance and the second parasitic capacitance are formed by adding one layer of underlying metal between a substrate of an integrated circuit and the pad, the pad and the underlying metal are spaced apart from each other to form the first parasitic capacitance, the pad is connected to the input terminal, the underlying metal and the substrate are spaced apart from each other to form the second parasitic capacitance, the underlying metal is connected to the output terminal, and the other end of the second parasitic capacitance is grounded by grounding the substrate, The microphone amplifier circuit includes: The method further includes a circuit point that satisfies a condition A that a voltage of the circuit point and a voltage of the input terminal are in phase with each other, a condition B that a voltage gain of the circuit point with respect to the input terminal is 0.8 or more and 1 or less, and a condition C that the circuit point is the output terminal, A microphone amplifier circuit, characterized in that the underlying metal is connected to the circuit point, and the pad is connected to the input terminal.

6. 1. A microphone amplifier circuit, comprising: The transistor includes a bias resistor, an input terminal, an output terminal, a microphone capacitance, a first parasitic capacitance, and a second parasitic capacitance; a gate of the transistor is connected to the input terminal, a source of the transistor is connected to the output terminal, and a drain of the transistor is connected to ground; one end of the bias resistor is connected to a bias voltage, and the other end of the bias resistor is connected to the input terminal; One end of the microphone capacitance is connected to a high bias voltage, and the other end of the microphone capacitance is connected to the input end; one end of the first parasitic capacitance is connected to the input terminal via a pad, the other end of the first parasitic capacitance is connected to the output terminal via an underlying metal, and one end of the second parasitic capacitance is connected to the output terminal via the underlying metal; the first parasitic capacitance and the second parasitic capacitance are formed by adding one layer of underlying metal between a substrate of an integrated circuit and the pad, the pad and the underlying metal are spaced apart from each other to form the first parasitic capacitance, the pad is connected to the input terminal, the underlying metal and the substrate are spaced apart from each other to form the second parasitic capacitance, the underlying metal is connected to the output terminal, and the other end of the second parasitic capacitance is grounded by grounding the substrate, The microphone amplifier circuit includes: The method further includes a circuit point that satisfies a condition A that a voltage of the circuit point and a voltage of the input terminal are in phase with each other, a condition B that a voltage gain of the circuit point with respect to the input terminal is 0.8 or more and 1 or less, and a condition C that the circuit point is the output terminal, A microphone amplifier circuit, characterized in that the underlying metal is connected to the circuit point, and the pad is connected to the input terminal.

7. The microphone amplifier circuit according to claim 6, further comprising a constant current source, one end of the constant current source being connected to a power supply voltage and the other end of the constant current source being connected to a source of the transistor and supplying a bias current to the transistor.

8. 7. The microphone amplifier circuit according to claim 5, wherein the microphone capacitance is a variable capacitance.

Images