CN110277967A - A kind of integrated circuit and the mobile terminal including the integrated circuit - Google Patents
A kind of integrated circuit and the mobile terminal including the integrated circuit Download PDFInfo
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/56—Modifications of input or output impedances, not otherwise provided for
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/181—Low-frequency amplifiers, e.g. audio preamplifiers
- H03F3/183—Low-frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
- H03F3/187—Low-frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only in integrated circuits
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/45—Differential amplifiers
- H03F3/45071—Differential amplifiers with semiconductor devices only
- H03F3/45479—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection
- H03F3/45928—Differential amplifiers with semiconductor devices only characterised by the way of common mode signal rejection using IC blocks as the active amplifying circuit
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- H—ELECTRICITY
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- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers
- H03G3/20—Automatic control
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Abstract
The present invention provides a kind of integrated circuit, which includes the first capacitance, amplifier and high-pass filter, and the high-pass filter is composed in parallel by the second capacitance and switch resistance, and the switch resistance is composed in series by switch and resistance；Wherein, one end of first capacitance connects the signal input part of the integrated circuit, the other end connects the negative input end of the amplifier, signal output end of the output end of the amplifier as the integrated circuit, and the high-pass filter connects the input terminal and output end of the amplifier.
Description
Technical Field
The present invention generally relates to the field of integrated circuits, and more particularly, to an integrated circuit and a mobile terminal including the same.
Background
Consumer electronics have been widely used in everyday life, where input processing of audio signals (e.g. speech or voice recordings) to convert speech into digital signals that can be processed by the electronics requires the use of amplifiers.
The processing effect of the audio signal, such as the voice quality of the call, the voice recognition rate of the smart speaker or the AI product, and the sound effect of the recording pen, is an important factor for the consumer to select the product. In order to improve the voice quality, such as suppression of noise in a call, picking up far-field sound by a smart speaker, etc., a plurality of microphones are usually used, and then the acoustic processing effect is enhanced by a software algorithm. For example, a smartphone uses more than 2 microphones to reduce noise, wherein one microphone collects noise around the environment, another microphone collects voice of a conversation, and signals collected by the 2 microphones are processed by an algorithm to obtain clearer voice. For another example, in order to effectively pick up sounds from various angles, a microphone array technology is used in smart speakers or AI products, and the number of microphones in a microphone array can reach 6-8. There is a trend towards increased microphones in consumer electronics.
As the number of microphones increases, the number of dc blocking capacitors required increases accordingly. The increase of the blocking capacitance brings about the following problems: (1) the number and cost of Bill of materials (BOM) are increased; (2) the layout area of a Printed Circuit Board (PCB) and the routing complexity of Electronic Design Automation (EDA) are increased, thereby increasing the difficulty of design; (3) the capacitance mismatch, typically the capacitance accuracy of a conventional X5R type 100nF capacitor, is typically ± 10%, and for an amplifier using differential input, the two capacitors may generate a ± 20% mismatch, which increases total harmonic Distortion plus Noise (total harmonic Distortion + Noise, THD + N), affecting audio performance.
For high-quality recording or Enhanced Voice Service (EVS) application in VOLTE, the cut-off frequency of the high-pass filter cannot be too large, and the value thereof needs to be lower than 20Hz to meet the requirement of the product for audio processing. Under the condition of f-3dB<At 20Hz, an equivalent input impedance of the amplifier is required to be above 4G ohms, and achieving this order of resistance on a chip with a 155mm process requires an area of about 4mm by 4mm, which is unacceptable in practical chip designs.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide an integrated circuit and a mobile terminal including the same, so as to improve the equivalent impedance of an amplifier, avoid the use of an off-chip blocking capacitor, and improve the signal processing performance of the integrated circuit.
In order to solve the above technical problem, an aspect of the present invention provides an integrated circuit, which includes a first blocking capacitor, an amplifier, and a high-pass filter, where the high-pass filter is formed by connecting a second blocking capacitor and a switch resistor in parallel, and the switch resistor is formed by connecting a switch and a resistor in series; one end of the first blocking capacitor is connected with a signal input end of the integrated circuit, the other end of the first blocking capacitor is connected with a negative input end of the amplifier, an output end of the amplifier is used as a signal output end of the integrated circuit, and the high-pass filter is connected with an input end and an output end of the amplifier.
In an embodiment of the present invention, the amplifier is a single-ended input amplifier, and a positive input terminal of the single-ended input amplifier is connected to a bias voltage.
In an embodiment of the present invention, the amplifier is a differential input amplifier, and a positive input end and a negative input end of the differential input amplifier are connected to two differential branches with the same structure.
In an embodiment of the invention, the switch of the switch resistor is a MOS transistor.
In an embodiment of the invention, the first dc blocking capacitor and/or the second dc blocking capacitor is a variable capacitor.
In an embodiment of the present invention, the variable capacitor is a switched capacitor array, the switched capacitor array is formed by connecting a plurality of capacitor switches in series and in parallel, and the capacitor switch string is formed by connecting capacitors and switches in series.
In an embodiment of the invention, the capacitance value of the first dc blocking capacitor and/or the second dc blocking capacitor is 10-100 pF.
In an embodiment of the invention, the integrated circuit is an audio signal integrated circuit.
In an embodiment of the present invention, the apparatus further includes an acoustic transducer, and the acoustic transducer is connected to the first dc blocking capacitor.
Another aspect of the invention provides a mobile terminal comprising an integrated circuit as described above, and further comprising a microphone, the microphone being connected to the integrated circuit.
Compared with the prior art, the invention has the following advantages: the invention provides an integrated circuit and a mobile terminal comprising the same, which improve the equivalent impedance of an amplifier through a switch resistor, avoid the use of an off-chip blocking capacitor and improve the signal processing performance of the integrated circuit.
Drawings
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below, wherein:
fig. 1 is a signal processing diagram of a microphone in an electronic product.
Fig. 2 is a block diagram of a typical microphone amplifier.
Fig. 3A is a schematic diagram of a typical switched capacitor.
FIG. 3B is a diagram of the gating signals of the switch of FIG. 3A.
Fig. 4A is an equivalent circuit diagram of fig. 3A.
Fig. 4B is an equivalent circuit diagram of fig. 4A.
FIG. 5 is a diagram of an integrated circuit according to an embodiment of the invention.
Fig. 6 is a schematic diagram of a capacitance value adjusting method of the variable capacitor in fig. 5.
Fig. 7A is an equivalent resistance working diagram according to an embodiment of the invention.
Fig. 7B is a logic diagram of switching cycle time states of the switch 701 in fig. 7A.
FIG. 8 is a diagram of an integrated circuit according to another embodiment of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described herein, and thus the present invention is not limited to the specific embodiments disclosed below.
As used in this application and the appended claims, the terms "a," "an," "the," and/or "the" are not intended to be inclusive in the singular, but rather are intended to be inclusive in the plural unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" merely indicate that steps and elements are included which are explicitly identified, that the steps and elements do not form an exclusive list, and that a method or apparatus may include other steps or elements.
It will be understood that when an element is referred to as being "on," "connected to," "coupled to" or "contacting" another element, it can be directly on, connected or coupled to, or contacting the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly on," "directly connected to," "directly coupled to" or "directly contacting" another element, there are no intervening elements present. Similarly, when a first component is said to be "in electrical contact with" or "electrically coupled to" a second component, there is an electrical path between the first component and the second component that allows current to flow. The electrical path may include capacitors, coupled inductors, and/or other components that allow current to flow even without direct contact between the conductive components.
Fig. 1 is a signal processing diagram of a microphone in an electronic product. As shown in fig. 1, the signal processing diagram includes a microphone 101, dc blocking capacitors 102 and 103, an amplifier 104, and an analog-to-digital converter 105.
The microphone 101 is used for collecting sound and converting a sound signal into a weak electrical signal. Amplifier 104 is used to amplify the electrical signal output by microphone 101 to approximately the full-scale input of analog-to-digital converter 105. The amplifier 104 may be comprised of a single stage or a multi-stage amplifier. The analog-to-digital converter 105 is used to convert the weak electrical signal into a digital signal for processing. A Digital Signal Processor (DSP) may process the Digital Signal.
Since different types of microphones 101 require different dc bias voltages, and the operating voltage of the amplifier 104 is generally determined, dc blocking capacitors 102 and 103 are required between the microphone 101 and the amplifier 104 to avoid interference when the microphone 101 and the amplifier 104 operate together. A dc blocking capacitor 102 is arranged in parallel with the dc blocking capacitor 103 for isolating mutual influence between the dc bias of the microphone 101 and the operating voltage of the amplifier 104. In some other embodiments, the number of microphones in the microphone array and the different types of amplifiers may have an effect on the number of dc blocking capacitances.
Fig. 2 is a block diagram of a typical microphone amplifier. As shown in fig. 2, the amplifier module 200 includes an input resistor 203, a load resistor 204, a bias voltage 205, and an amplifier 206. The input resistor 203 of a typical amplifier 206 has a resistance value in the range of 104～107Omega is between. Also shown in fig. 2 are a signal input 201, an off-chip dc blocking capacitor 202 and a signal output 207. The blocking capacitor 202 and the input resistor 203 constitute a high pass filter for filtering low frequency dc components of the input signal, the high pass filter having a cut-off frequency f-3dBCutoff frequency f-3dBThe calculation formula of (2) is as follows:
for high quality microphone electronics, the cut-off frequency of the filtering needs to be below 20 Hz. If the requirement of the filter cut-off frequency is met, the size of the blocking capacitor ranges from 10nF to 10 muF. The increase of the number of the blocking capacitors and the increase of the number capacitors have the defects of increasing the area of a circuit board, increasing the difficulty of audio algorithm processing and the like. If the capacitor or the resistor is directly integrated into the amplifier module, the chip area is obviously increased, and the integration in practical application cannot be realized. In the prior art, a larger equivalent resistance is realized by adopting a switched capacitor mode to weaken the adverse effect of the increase of the number of blocking capacitors on an integrated circuit.
Fig. 3A is a schematic diagram of a typical switched capacitor. As shown in fig. 3A, 301 and 305 are power supplies, 302 and 303 are a pair of contact switches, and 304 is a charge/discharge capacitor. In chip design, 302 and 303 can use MOS tube as switch. When 302 and 303 are on, they have a lower on-resistance; when 302 and 303 are off, they have a very high equivalent resistance. FIG. 3B is a diagram of the gating signals of the switch of FIG. 3A. As shown in fig. 3B, the switches 302 and 303 are respectively controlled by a set of clock signals which do not overlap each other and have different directions.
Fig. 4A is an equivalent circuit diagram of fig. 3A. As shown in fig. 4A, switches 302 and 303 in fig. 3 may be equivalent to switch 404. When the voltage V of the power source 4011Greater than the voltage V of the power supply 4032When switch 404 is switched off from power source 401, power source 401 begins to charge capacitor 402. After the charging is completed, the voltage across the capacitor 402 is V1(ii) a On the next clock cycle, capacitor 402 begins to discharge when switch 404 is switched off to power supply 403. At this time, the total charge flowing from the power source 401 to the power source 403 is:
ΔQ＝C(V1-V2) (2)
known switch 404 is at f per secondckThe amount of charge transferred from the power source 401 to the power source 403 within 1s is equivalent to the average current I by switching back and forth between the left and right nodes for each cycleAVGThe formula is as follows:
IAVG＝fckC(V1-V2) (3)
fig. 4B is an equivalent circuit diagram of fig. 4A. When f is shown in FIG. 4BckFrequency ratio power supplies 401 and403 is much higher, it can be considered that the charge transfer from 401 to 403 is continuous, the whole charge transfer process can be equivalent to a resistor 405 by the switch 404 and the capacitor 402, and the calculation formula of the equivalent resistor 405 is as follows:
in equation (3), assume fckIs 100kHz, C is 1pF, then ReqIs 10 M.OMEGA.. Reduction of C and fckCan increase the equivalent resistance, but this is difficult to achieve in practical designs. Therefore, it can be seen from equation (3) that it is difficult to achieve an equivalent resistance of 1G Ω by switching the capacitors.
FIG. 5 is a diagram of an integrated circuit according to an embodiment of the invention. As shown in fig. 5, the integrated circuit 500 includes a first dc blocking capacitor 502, an amplifier 509, and a high pass filter 511. Also shown in fig. 5 are a signal input 501, a bias voltage 503, a switch 504, a second dc blocking capacitor 507, a resistor 508 and a signal output 510.
The first blocking capacitor 502 has one end connected to the signal input terminal 501 of the integrated circuit 500 and the other end connected to the negative input terminal 509a of the amplifier 509. The positive input 509b of the amplifier is connected to a bias voltage 503. An output 509c of the amplifier 509 serves as a signal output 510 of the integrated circuit 500. The high-pass filter 511 is formed by connecting the second dc blocking capacitor 507 in parallel with a switch resistor, and the switch resistor is formed by connecting the switch 504 and the resistor 508 in series. The switch 504 may be a MOS transistor, and each of the first dc blocking capacitor 502 and the second dc blocking capacitor 507 may be a variable capacitor. The variable capacitor can be a switched capacitor array, the switched capacitor array is formed by connecting a plurality of capacitor switches in series and in parallel, and the capacitor switch string is formed by connecting capacitors and switches in series. The high pass filter 511 is connected to the negative input terminal 509a and the output terminal 509c of the amplifier 509. The structure of the switched capacitor array will be described later.
In this embodiment, the integrated circuit 500 in fig. 5 may be an audio signal integrated circuit, wherein the amplifier 509 is a single-ended input amplifier, and the positive input 509b of the amplifier 509 is connected to a bias voltage 503. The integrated circuit 500 may further comprise an acoustic transducer coupled to the first dc blocking capacitance 502.
The operation of the integrated circuit 500 is described below with reference to fig. 5.
As shown in fig. 5, the first dc blocking capacitor 502 and the second dc blocking capacitor 507 replace the off-chip dc blocking capacitor 202 and the input resistor 203 in fig. 2, so that a microphone amplifier integrated circuit without an off-chip dc blocking capacitor can be realized. The first dc blocking capacitor 502 and the second dc blocking capacitor 507 constitute an inverting amplifier for amplifying the input signal, and the amplification gain a is:
the minus sign in equation (5) represents only the phase inversion of the output signal and the input signal. C502And C507The capacitance values, C, of the first DC blocking capacitor 502 and the second DC blocking capacitor 507502And C507The capacity value of the device can be adjusted.
Fig. 6 is a schematic diagram of a capacitance value adjusting method of the variable capacitor in fig. 5. As shown in fig. 6, the variable capacitor is a switched capacitor array 600, which is formed by connecting a plurality of capacitor switches in series and in parallel, and the capacitor switch series is formed by connecting capacitors and switches in series.
In fig. 6, there are three capacitor switch strings, each composed of a capacitor 601 and a switch 604, a capacitor 602 and a switch 605, and a capacitor 603 and a switch 606 connected in series. The capacitors 601, 602, and 603 are three capacitors having different capacitance values. The switches 604, 605 and 606 are controlled by three external control signals 607, 608 and 609, respectively, and when the control signal is high, the capacitors connected by the switches controlled by the control signal are connected in parallel to the capacitor array. In the present embodiment, the capacitance value of the first dc blocking capacitor 502 and/or the second dc blocking capacitor 507 of the variable capacitor implemented by the capacitance value adjusting method of the variable capacitor shown in fig. 6 is adjusted in a range of 10-100 pF. In some other embodiments, the number of the capacitor switch strings can be changed according to the capacitance value adjusting range of the variable capacitor.
In fig. 5, the high-pass filter 511 is formed by connecting the second dc blocking capacitor 507 in parallel with a switch resistor, and the switch resistor is formed by connecting the switch 504 and the resistor 508 in series. In the present embodiment, the switch resistor formed by connecting the switch 504 and the resistor 508 in series realizes an equivalent resistor with a high resistance value, and can satisfy the cutoff frequency f of the high-pass filter 511-3dBTo meet high quality audio operating requirements (i.e.: f)-3dB< 20Hz) without increasing the chip area.
Fig. 7A is an equivalent resistance working diagram according to an embodiment of the invention. As shown in fig. 7, a switch 701 is connected in series with a resistor 702 to form an equivalent resistor 700.
When switch 701 is closed, resistor 702 is on; when switch 701 is open, resistor 702 is open in the integrated circuit and the equivalent resistance approaches infinity. The switch 701 may be an MOS transistor with low on-resistance, and when the MOS transistor is turned on, the equivalent resistance may be smaller than the resistance of the resistor 702; when the MOS transistor is turned off, the equivalent resistance approaches infinity. Fig. 7B is a logic diagram of switching cycle time states of the switch 701 in fig. 7A. As shown in fig. 7B, the time of one switching cycle T of the switch 701 includes a switch-on time 703 (S)on) And switch on time 704 (S)off) The formula is as follows:
T＝Son+Soff (6)
from equation (6), the operating frequency f of switch 701 can be definedckComprises the following steps:
since the switch 701 operates in switching on and off, f is provided for ensuring continuity of operation of the audio signalckA maximum frequency greater than the audio frequency (i.e., 20kHz) is required, in this embodiment, fckIs set to be 100kHz 5 times the maximum frequency of the audio. During a switching period T, the amount of charge flowing through the resistor is defined as Q:
Q＝it＝iT (8)
the current i is decomposed into a current i flowing through the resistor 702 when the switch 701 is turned offoffAnd a current i flowing through the resistor 702 when the switch 701 is turned onon：
Q＝ion*Son+ioff*Soff (9)
In equations (10) to (12), V is a power supply voltage value, R is a resistance value of the resistor 702, and R isoffApproaching infinity, ReqIs the resistance value of the equivalent resistor, ieqIs the equivalent current flowing through resistor 702 during one switching period T. In conjunction with equations (8) and (9), the following equation can be derived:
Q＝ieq*(Son+Soff)＝ion*Son+ioff*Soff (13)
substituting equations (10), (11) and (12) into equation (13), equation (13) can be modified as:
since R is turned off when the switch 701 is turned offoffThe approach is infinity, defineThen the following formula is given:
in the present embodiment, equivalent resistance of 1G Ω or more can be realized by switching the resistor, which is described by a fixed value in conjunction with the derivation of the above formula. In the present embodiment, the resistor 702 is a Poly-High resistance (High Poly-resistance). The resistance of the resistor 702 is set to 10M omega, and the operating frequency f of the switch 701 is set tock100kHz, a switching period T of 10 mus is obtained from the formula (7), and the switch opening time S is setonIs 50ns, R can be obtained from the formula (16)eqIs 2 G.OMEGA.. On the basis of unchanged switching period T, the on-time S of the switch is shortenedonGreater R may be obtainedeqThe resistance value.
In another embodiment, the amplifier in the integrated circuit may also be a differential input amplifier. FIG. 8 is a diagram of an integrated circuit according to another embodiment of the present invention. As shown in fig. 8, integrated circuit 800 includes two structurally identical differential branches and amplifier 813.
The negative input terminal of the amplifier 813 is connected to a differential branch, which is composed of a first dc blocking capacitor 803, a switch 805, a second dc blocking capacitor 811, and a resistor 815, wherein the high pass filter 818 is composed of the second dc blocking capacitor 811 and a switch resistor, and the switch resistor is composed of the switch 805 and the resistor 815. The positive input terminal of the amplifier 814 is connected to another differential branch, which is composed of a first dc blocking capacitor 804, a switch 806, a second dc blocking capacitor 812 and a resistor 814, wherein the high-pass filter 819 is composed of the second dc blocking capacitor 812 and a switch resistor, and the switch resistor is composed of the switch 806 and the resistor 814. The positive input end and the negative input end of the amplifier 813 are connected with two differential branches with the same structure.
Also shown in fig. 8 are two signal inputs 801, 802 and two signal outputs 816 and 817. Signal input terminal 801 and signal output terminal 817 are connected to the differential branch of amplifier 813 connected at the negative input terminal, and signal input terminal 802 and signal output terminal 816 are connected to the differential branch of amplifier 813 connected at the positive input terminal.
In the integrated circuit 800, a microphone amplifier integrated circuit without an off-chip blocking capacitor can be realized with a variable capacitor and a switch resistor having the same structure and operation principle as those in fig. 6 to 7. With the differential input operational amplifier, if the first blocking capacitors 803 and 804 are not matched, the differential signal output by the microphone will form a large difference in phase and amplitude after passing through the unmatched capacitors, which deteriorates the key indicator of audio frequency, such as THD + N increase.
The pair of first blocking capacitors 803 and 804 adopted in the embodiment of fig. 8 is a pair of capacitors with high matching, the embodiment adopts a layout matching mode to repair and adjust the two capacitors, the relative precision of the two capacitors after the repair and adjustment can reach 0.1%, the complete matching of the two capacitors is ensured, and compared with the external capacitor, the audio performance is obviously improved.
On the basis of the existing microphone amplifier design method, the invention has the following improvement points:
(1) a method for switching a resistor is provided, a resistor with enough (more than G) equivalent resistance is integrated in a chip by using the method, a method for designing a microphone amplifier without an off-chip blocking capacitor is realized, the off-chip blocking capacitor can be omitted while the audio performance is improved, the number and cost of devices designed by a peripheral circuit are reduced, and the swing area and wiring difficulty of a circuit board are saved.
(2) The mode of the amplifier in the present invention may be a single-ended input mode or a differential input mode. When the differential input mode method is adopted, the input capacitance of the amplifier adopts a layout matching mode, the relative precision of the differential capacitance after layout trimming can reach 0.1%, and the microphone amplifier adopting a differential output working mode is optimized.
(3) The high-pass filter is composed of a switch resistor and an adjustable capacitor array, the adjustable capacitor array realizes that the gain of the microphone amplifier is adjustable, the cut-off frequency of the high-pass filter is less than 20Hz, and the requirements of high-quality electronic products of microphones are met.
(4) The high-resistance equivalent resistance realized by the switch resistance is not only applied to the microphone amplifier circuit, but also applied to other circuits needing to improve the performance by realizing the high-resistance equivalent resistance.
This application uses specific words to describe embodiments of the application. Reference throughout this specification to "one embodiment," "an embodiment," and/or "some embodiments" means that a particular feature, structure, or characteristic described in connection with at least one embodiment of the present application is included in at least one embodiment of the present application. Therefore, it is emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, some features, structures, or characteristics of one or more embodiments of the present application may be combined as appropriate.
Although the present invention has been described with reference to the present specific embodiments, it will be appreciated by those skilled in the art that the above embodiments are merely illustrative of the present invention, and various equivalent changes and substitutions may be made without departing from the spirit of the invention, and therefore, it is intended that all changes and modifications to the above embodiments within the spirit and scope of the present invention be covered by the appended claims.
Claims (10)
1. An integrated circuit comprises a first blocking capacitor, an amplifier and a high-pass filter, wherein the high-pass filter is formed by connecting a second blocking capacitor and a switch resistor in parallel, and the switch resistor is formed by connecting a switch and a resistor in series; wherein,
one end of the first blocking capacitor is connected with a signal input end of the integrated circuit, the other end of the first blocking capacitor is connected with a negative input end of the amplifier, an output end of the amplifier is used as a signal output end of the integrated circuit, and the high-pass filter is connected with the input end and the output end of the amplifier.
2. The integrated circuit of claim 1, wherein the amplifier is a single-ended input amplifier, and a positive input of the single-ended input amplifier is connected to a bias voltage.
3. The integrated circuit of claim 1, wherein the amplifier is a differential input amplifier, and a positive input and a negative input of the differential input amplifier are connected to two differential branches having the same structure.
4. The integrated circuit of claim 1, wherein the switch of the switch resistor is a MOS transistor.
5. The integrated circuit of claim 1, wherein the first dc blocking capacitance and/or the second dc blocking capacitance is a variable capacitance.
6. The integrated circuit of claim 5, wherein the variable capacitor is a switched capacitor array, the switched capacitor array comprising a plurality of capacitor switches connected in series and in parallel, the capacitor switch string comprising a capacitor and a switch connected in series.
7. The integrated circuit of claim 1, wherein the first dc blocking capacitance and/or the second dc blocking capacitance has a capacitance value of 10-100 pF.
8. The integrated circuit of claim 1, wherein the integrated circuit is an audio signal integrated circuit.
9. The integrated circuit of claim 1, further comprising an acoustic transducer coupled to the first dc blocking capacitance.
10. A mobile terminal comprising the integrated circuit according to any of claims 1-9, and further comprising a microphone, the microphone being connected to the integrated circuit.
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