Differential amplification circuit and desktop microphone

Abstract

This application relates to the field of microphone technology, and discloses a differential amplifier circuit and a desktop microphone. The circuit is used to amplify and process the differential audio signal of the desktop microphone. Its features include an input signal receiving and DC bias module, a differential transistor amplifier module, a fully differential operational amplifier module, a cross-feedback network module, a power supply and reference voltage module, and an output signal processing module connected in sequence. A common-mode negative feedback network for suppressing common-mode signals is provided between the emitters of the two corresponding symmetrical amplification paths of the differential transistor amplifier module. A cross-feedback network module is provided between the differential output terminal and the differential input terminal of the fully differential operational amplifier module to form an AC differential negative feedback loop. The power supply and reference voltage module includes at least two reference voltage units, which respectively provide DC bias for the differential transistor amplifier module and set the output common-mode level for the fully differential operational amplifier module.

Description

Technical Field

[0001] This application relates to the field of microphone technology, specifically microphone audio preamplification processing technology, and discloses a differential amplifier circuit and a desktop microphone. Background Technology

[0002] Currently, microphone preamplifier circuits are mainly divided into two categories: single-ended amplification architecture and conventional differential amplification architecture. Single-ended amplification architecture has a simple structure, but its ability to suppress common-mode electromagnetic interference in complex desktop electrical environments is extremely weak. It is highly susceptible to interference from USB switching power supply ripple, high-frequency digital noise from computer motherboards, and environmental radio frequency radiation, resulting in audible noise and power frequency noise floor. At the same time, when amplifying the weak microvolt-level signal output by the microphone, the single-ended amplification architecture needs to provide a high gain of more than 60dB, which will synchronize the inherent thermal noise and flicker noise of the amplification circuit, severely limiting the improvement of the signal-to-noise ratio and making it impossible to reproduce the subtle details of the sound. Summary of the Invention

[0003] This application provides a differential amplifier circuit and a desktop microphone, aiming to address the problem that microphone preamplifier circuits are mainly divided into two categories: single-ended amplifier architecture and conventional differential amplifier architecture. Single-ended amplifier architecture has a simple structure, but its ability to suppress common-mode electromagnetic interference in the complex electrical environment of a desktop is extremely weak, and it is highly susceptible to interference from USB switching power supply ripple, high-frequency digital noise from the computer motherboard, and environmental radio frequency radiation.

[0004] In a first aspect, embodiments of this application provide a differential amplifier circuit for amplifying differential audio signals from a desktop microphone, comprising an input signal receiving and DC biasing module, a differential transistor amplification module, a fully differential operational amplifier module, a cross-feedback network module, a power supply and reference voltage module, and an output signal processing module connected in sequence. The differential transistor amplifier module has a common-mode negative feedback network between the emitters of the two corresponding symmetrical amplification paths for suppressing common-mode signals. The fully differential operational amplifier module is provided with a cross-feedback network module between its differential output terminal and differential input terminal to form an AC differential negative feedback loop. The power supply and reference voltage module includes at least two reference voltage units, which provide DC bias for the differential transistor amplifier module and set the output common-mode level for the fully differential operational amplifier module, respectively.

[0005] In some embodiments, the two symmetrical amplification paths of the differential transistor amplification module are constructed using a pair of identical bipolar transistors integrated in the same package, and the two transistors have matched temperature characteristics and electrical parameters.

[0006] In some embodiments, the common-mode negative feedback network includes a common-mode feedback resistor and a high-frequency compensation capacitor connected in parallel. The common-mode negative feedback network provides a low-impedance path for the common-mode signal of the two amplification paths and presents a high impedance for the differential-mode signal.

[0007] In some embodiments, the emitters of the two amplification paths of the differential transistor amplifier module are grounded through independent emitter resistors to form local current negative feedback for improving the linearity of signal amplification.

[0008] In some embodiments, the input signal receiving and DC biasing module includes two symmetrically arranged input matching units. The two differential input audio signals are respectively connected to the two input terminals of the differential transistor amplifier module through the corresponding input matching units, providing a reference voltage unit for DC biasing of the differential transistor amplifier module, and synchronously injected into the corresponding input terminals through the two input matching units.

[0009] In some embodiments, the cross-feedback network module includes two symmetrically arranged AC coupling units. The inverting output terminal of the fully differential operational amplifier module is connected to its non-inverting input terminal via the first AC coupling unit, and the non-inverting output terminal is connected to its inverting input terminal via the second AC coupling unit, thus forming a cross-coupled AC differential negative feedback loop.

[0010] In some embodiments, the non-inverting input and inverting input of the fully differential operational amplifier module are grounded through independent grounding resistors to provide a DC path for the input bias current of the operational amplifier. The grounding resistors and the corresponding AC coupling units cooperate to form a high-pass filter network.

[0011] In some embodiments, the fully differential operational amplifier module is provided with a common-mode voltage control terminal, which is used to set the reference voltage unit for the output common-mode level. The reference voltage unit is connected to the common-mode voltage control terminal, and the common-mode level of the two differential output terminals is locked through the common-mode feedback loop inside the operational amplifier.

[0012] In some embodiments, the output signal processing module includes two symmetrically arranged DC blocking coupling units. The two differential output signals of the fully differential operational amplifier module are output through the corresponding DC blocking coupling units to block the DC component and output a pure AC differential audio signal.

[0013] Secondly, embodiments of this application provide a desktop microphone, including a microphone body and a differential amplifier circuit as provided in any embodiment of this application.

[0014] This application employs a two-stage fully differential amplification architecture, coupled with a dedicated emitter common-mode negative feedback network and a cross-differential negative feedback loop, to achieve deep suppression of wideband common-mode noise. Simultaneously, it significantly optimizes the circuit's inherent noise floor, perfectly adapting to high-fidelity amplification of weak signals at the microvolt level for desktop microphones, preventing circuit noise from drowning out sound details. The fully differential symmetrical architecture naturally cancels even-order harmonic distortion, and the differential negative feedback loop achieves stable gain and linearity across the entire audio frequency range, ensuring the original fidelity of the audio signal and preventing sound quality degradation caused by distortion. Two independent reference voltage units enable independent and precise control of the input stage DC bias and the output stage common-mode level, allowing flexible adaptation to different types of microphone components and subsequent analog-to-digital conversion circuits. It also effectively suppresses operating point shift caused by temperature drift, improving the long-term reliability of the circuit.

[0015] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic block diagram of the differential amplifier circuit provided in the embodiments of this application; Figure 2 This is a circuit diagram of the differential amplifier circuit provided in the embodiments of this application; Figure 3 This is a schematic diagram of the structure of the desktop microphone provided in an embodiment of this application.

[0018] Explanation of reference numerals in the attached figures: 1000, Desktop microphone; 100. Differential amplifier circuit; 10. Input signal receiving and DC bias module; 20. Differential transistor amplifier module; 30. Fully differential operational amplifier module; 40. Cross-feedback network module; 50. Power supply and reference voltage module; 60. Output signal processing module; 200. Microphone body.

[0019] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] The flowchart shown in the attached diagram is for illustrative purposes only and does not necessarily include all content and operations / steps, nor does it necessarily have to be performed in the order described. For example, some operations / steps can be broken down, combined, or partially merged, so the actual execution order may change depending on the actual situation.

[0022] It should be understood that, in order to clearly describe the technical solutions of the embodiments of the present invention, the terms "first" and "second" are used in the embodiments of the present invention to distinguish identical or similar items with essentially the same function and effect. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and the terms "first" and "second" are not necessarily different.

[0023] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0024] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0025] Currently, microphone preamplifier circuits are mainly divided into two categories: single-ended amplification architecture and conventional differential amplification architecture. Single-ended amplification architecture has a simple structure, but its ability to suppress common-mode electromagnetic interference in complex desktop electrical environments is extremely weak. It is highly susceptible to interference from USB switching power supply ripple, high-frequency digital noise from computer motherboards, and environmental radio frequency radiation, resulting in audible noise and power frequency noise floor. At the same time, when amplifying the weak microvolt-level signal output by the microphone, the single-ended amplification architecture needs to provide a high gain of more than 60dB, which will synchronize the inherent thermal noise and flicker noise of the amplification circuit, severely limiting the improvement of the signal-to-noise ratio and making it impossible to reproduce the subtle details of the sound.

[0026] While conventional differential amplifier architectures possess a certain degree of common-mode interference suppression capability, they still suffer from a series of insurmountable technical defects: First, the input stage of existing differential amplifier architectures mostly adopts a basic differential pair transistor structure, without setting up a dedicated common-mode negative feedback network for wideband common-mode interference. This results in insufficient full-band suppression capability against low-frequency power frequency interference and high-frequency switching power supply noise, allowing residual common-mode noise to enter the amplification link along with the signal and thus failing to be effectively filtered out. Second, existing differential amplifier circuits mostly use a single reference voltage to complete both input stage biasing and output stage level control, failing to simultaneously address input stage biasing and output stage level control. The stability of the bias and the level matching requirements of the output stage for the subsequent analog-to-digital conversion circuit can easily lead to a limited dynamic range of the signal, or even saturation cutoff distortion. Thirdly, the feedback loops of existing differential amplifier circuits mostly adopt single-ended feedback or conventional in-phase differential feedback structures, which cannot stabilize AC gain and frequency response across the entire audio frequency band. They are prone to problems such as low-frequency phase shift and transient response distortion, and can never simultaneously meet the multiple core requirements of low noise, high linearity, and high common-mode rejection capability. They also cannot meet the requirements of high-fidelity, low noise floor, and strong anti-interference of high-end desktop microphones.

[0027] To solve the above problems, please refer to Figure 1 and Figure 2 This application provides a differential amplifier circuit 100 for a desktop microphone, including amplification processing for differential audio signals from the desktop microphone. The circuit comprises an input signal receiving and DC bias module 10, a differential transistor amplifier module 20, a fully differential operational amplifier module 30, a cross-feedback network module 40, a power supply and reference voltage module 50, and an output signal processing module 60, connected in sequence. The differential transistor amplifier module 20 has a common-mode negative feedback network for suppressing common-mode signals between the emitters of the two corresponding symmetrical amplification paths. The fully differential operational amplifier module 30 has a cross-feedback network module 40 between its differential output and differential input terminals to form an AC differential negative feedback loop. The power supply and reference voltage module 50 includes at least two reference voltage units, which provide DC bias to the differential transistor amplifier module 20 and set the output common-mode level for the fully differential operational amplifier module 30, respectively.

[0028] Specifically, the differential amplifier circuit 100 for desktop microphones provided in this application embodiment is a low-noise, high common-mode rejection, and high-fidelity audio preamplifier solution for desktop microphone scenarios such as professional recording, high-end conferences, and content creation. Its core function is to amplify the weak millivolt / microvolt level differential audio signal output by the microphone with low distortion and high anti-interference capabilities, adapting to the sampling requirements of the subsequent analog-to-digital converter (ADC), and solving the core pain points in the prior art such as the contradiction between weak signal amplification and noise suppression, insufficient common-mode interference suppression capability, nonlinear distortion, and poor temperature drift stability.

[0029] The core of the circuit adopts a fully differential symmetrical architecture, consisting of a cascaded input signal receiving and DC biasing module 10, a differential transistor amplifier module 20, a fully differential operational amplifier module 30, and an output signal processing module 60. It also includes a cross-feedback network module 40 and a power supply and reference voltage module 50. Specifically, a common-mode negative feedback network for suppressing common-mode signals is provided between the emitters of the two symmetrical amplification paths of the differential transistor amplifier module 20. A cross-feedback network module 40 is provided between the differential output and differential input terminals of the fully differential operational amplifier module 30 to form an AC differential negative feedback loop. The power supply and reference voltage module 50 is equipped with at least two independent reference voltage units, providing DC bias for the differential transistor amplifier module 20 and setting the output common-mode level for the fully differential operational amplifier module 30, ultimately achieving low-noise, high common-mode rejection, high linearity, and high-stability audio amplification.

[0030] The input signal receiving and DC bias module 10 serves as the signal input interface for the entire amplifier circuit. Its core functions include impedance matching, current limiting protection, and high-pass filtering of the microphone differential signal. Simultaneously, it injects a precise DC bias voltage into the subsequent differential transistor amplifier module 20 to ensure that the transistor operates within the appropriate linear amplification range.

[0031] The module is configured with two fully symmetrical input matching units, corresponding to the non-inverting input terminal IN_P and the inverting input terminal IN_N of the differential audio signal, respectively. IN_P is connected to the base of the first transistor in the differential transistor amplifier module 20 via the first input matching resistor R1, and IN_N is connected to the base of the second transistor in the differential transistor amplifier module 20 via the second input matching resistor R4. The first reference voltage unit VREF1 in the power supply and reference voltage module 50, used for input stage bias, is synchronously injected into the base nodes of the two transistors via R1 and R4, making the base voltage of the two transistors VREF1 superimposed with the corresponding input AC differential signal, thus achieving synchronous injection of AC signal coupling and DC bias. Simultaneously, R1 and R4, together with the microphone's output capacitor, form a high-pass filter network to filter out ultra-low frequency unwanted signals, while also achieving impedance matching and input current limiting protection to prevent damage to subsequent transistor devices.

[0032] The differential transistor amplifier module 20 serves as the core of the pre-amplification of the circuit. It adopts a fully symmetrical dual-channel differential amplifier architecture to achieve low-noise pre-amplification of weak differential signals. At the same time, through the built-in common-mode negative feedback network and local negative feedback design, it significantly improves the common-mode interference suppression capability and signal amplification linearity. It is the core foundation for the low-noise and high anti-interference performance of the entire circuit.

[0033] The core of the module employs two symmetrical amplification paths, each composed of a paired bipolar junction transistor pair (BJT) Q4. The left transistor forms the first amplification path, and the right transistor forms the second. The collectors of the two transistors are connected to the power supply VCC via load resistors R2 and R3, respectively, while their emitters are grounded via independent emitter resistors R15 and R16, forming local current negative feedback. A common-mode negative feedback network, consisting of a common-mode feedback resistor R14 and a high-frequency compensation capacitor C7, is connected in parallel between the emitters of the two transistors. This network presents low impedance to the two input common-mode signals, forcing the common-mode voltages of the two emitters to converge and suppressing the amplification of common-mode interference. It also presents high impedance to the two inversely phased differential-mode signals, ensuring that the amplification of the useful differential signal is not affected.

[0034] During operation, the differential voltage signals from the two base inputs are amplified by the transistor and converted into collector current changes. These changes are then converted back into differential voltage signals by the collector load resistors R2 and R3 and output to the subsequent fully differential operational amplifier module 30. The emitter resistors R15 and R16 suppress the nonlinearity of the transistor through current negative feedback, improving the amplification linearity. The common-mode negative feedback network effectively suppresses common-mode noise such as power frequency, power supply ripple, and radio frequency radiation in the first stage of amplification, reducing the interference processing pressure on subsequent circuits.

[0035] The fully differential operational amplifier module 30 serves as the main amplification core of the circuit. It employs a high-performance fully differential operational amplifier U1 to perform high-gain, high common-mode rejection ratio amplification on the pre-amplified differential signal. At the same time, it precisely locks the output common-mode level through the built-in common-mode feedback loop, achieving perfect level matching with the subsequent ADC and ensuring maximum utilization of the signal dynamic range.

[0036] The non-inverting input of the fully differential operational amplifier U1 is connected to the collector output of the first transistor in the differential transistor amplifier module 20, and the inverting input is connected to the collector output of the second transistor in the differential transistor amplifier module 20, receiving the pre-amplified differential voltage signal. U1 is configured with an inverting output terminal OUT_P and a non-inverting output terminal OUT_N to output two amplified differential signals with opposite phases and equal amplitudes. U1 has a dedicated common-mode voltage control terminal VOCM. The second reference voltage unit VREF2 in the power supply and reference voltage module 50, which is used for output level setting, is connected to this VOCM pin. Through the common-mode feedback loop inside U1, the average voltage of the two output terminals (i.e., the output common-mode voltage) is forced to strictly follow VREF2, accurately matching the input common-mode voltage range of the subsequent ADC, avoiding signal dynamic range limitation or saturation clipping distortion.

[0037] The cross-feedback network module 40 is connected between the differential output and differential input terminals of the fully differential operational amplifier module 30, forming a cross-coupled AC differential negative feedback loop. Its core function is to stabilize the AC gain and frequency response of the circuit, while providing a DC path for bias current to the operational amplifier. Together, they form a high-pass filter network to set the low-frequency cutoff frequency of the circuit.

[0038] The module is configured with two symmetrical AC coupling units. The first AC coupling unit is a DC blocking capacitor C1, and the second AC coupling unit is a DC blocking capacitor C8. The inverting output terminal OUT_P of U1 is connected to its non-inverting input terminal via C1, and the non-inverting output terminal OUT_N of U1 is connected to its inverting input terminal via C8, forming a cross-coupled AC differential negative feedback loop. This negative feedback stabilizes the AC gain of the circuit, optimizes the frequency response flatness across the entire audio frequency band, and improves the circuit's anti-interference and stability. Simultaneously, the non-inverting input terminal of U1 is grounded via an independent grounding resistor R9, and the inverting input terminal is grounded via an independent grounding resistor R13. These two grounding resistors provide a DC path for the input bias current of U1, preventing DC offset caused by charge accumulation. Furthermore, R9 and C1, and R13 and C8 respectively cooperate to form a high-pass filter network, accurately setting the low-frequency cutoff frequency of the circuit and filtering out unwanted ultra-low frequency noise signals.

[0039] The output signal processing module 60 serves as the output stage of the circuit. Its core function is to achieve DC blocking coupling of the amplified signal, blocking the DC common-mode voltage output by the operational amplifier, and outputting only a pure AC differential audio signal to meet the input requirements of subsequent audio processing or sampling circuits.

[0040] The module is configured with two symmetrical DC blocking coupling units. The first DC blocking coupling unit is a DC blocking capacitor C2, and the second DC blocking coupling unit is a DC blocking capacitor C4. The inverting output terminal OUT_P of U1 is connected to the final non-inverting output terminal OUT_P of the circuit via C2, and the non-inverting output terminal OUT_N of U1 is connected to the final inverting output terminal OUT_N of the circuit via C4. Through the DC blocking effect of C2 and C4, the DC common-mode voltage set by VREF2 at the output terminal of U1 is completely blocked, allowing only AC differential signals in the 20Hz-20kHz audio frequency band to pass through. The final output is a pure, DC-free amplified audio differential signal, completing the entire signal amplification process.

[0041] The power supply and reference voltage module 50 provides a stable power supply and a precise reference voltage for the entire circuit. It is equipped with at least two independent reference voltage units to independently control the DC bias of the input stage and the common-mode level of the output stage, thereby improving the adaptability and stability of the circuit.

[0042] The core of the module includes a power supply unit and two independent reference voltage units. The power supply unit outputs power VCC to power the fully differential operational amplifier U1, and simultaneously provides power and load support to the collectors of the differential transistor pair Q4 via resistors R2 and R3. Decoupling capacitors are included in the power supply lines to filter out power supply noise. The first reference voltage unit, VREF1, is a precision reference source output. Through input matching resistors R1 and R4, it provides precise DC bias to the two bases of the differential transistor pair Q4, ensuring that the transistors operate in the linear amplification range. The second reference voltage unit, VREF2, is an independent precision reference source output, connected to the VOCM pin of the fully differential operational amplifier U1, precisely setting the common-mode level of the output signal. Both reference voltages are independently adjustable, adaptable to the bias requirements of different types of electret rectifiers and MEMS microphones, as well as the input level requirements of different ADC specifications, significantly improving the circuit's scenario adaptability.

[0043] In some embodiments, the two symmetrical amplification paths of the differential transistor amplifier module 20 are constructed by pairing bipolar transistors of the same type integrated in the same package, and the two transistors have matched temperature characteristics and electrical parameters.

[0044] This embodiment optimizes the design of the core amplification device of the differential transistor amplifier module 20, and solves the problems of poor parameter matching, inconsistent temperature characteristics, large temperature drift, insufficient common-mode rejection capability, and poor mass production consistency of existing discrete transistor differential pairs. By using paired integrated bipolar transistor pairs in the same package, the electrical parameters and temperature characteristics of the two amplification paths are highly matched, which greatly improves the thermal stability, common-mode rejection capability and mass production consistency of the circuit.

[0045] The differential transistor amplifier module 20 has two symmetrical amplification paths. The core amplification device uses a pair of identical dual NPN transistors Q4 integrated in the same package. The two transistors of this pair are manufactured on the same wafer and integrated in the same package, enjoying completely consistent thermal environment and operating temperature. They have strictly matched electrical parameters (including emitter-junction voltage drop Vbe, current amplification factor β, junction capacitance, noise characteristics, etc.) and temperature coefficient.

[0046] During circuit operation, transistor parameter drift caused by changes in ambient temperature or heat generated by device operation manifests as highly synchronized common-mode changes in the two symmetrical paths. This can be effectively suppressed by differential architecture and common-mode negative feedback network, preventing parameter drift from being converted into differential-mode signal offset and noise. This solves the problems of operating point offset, gain fluctuation, and audible temperature drift noise caused by temperature drift. At the same time, the parameter consistency of integrated paired transistors is much higher than that of discrete transistors, which can significantly improve the common-mode rejection ratio of the circuit and reduce the difficulty of device pairing in mass production. It can ensure high consistency of product performance without complex individual calibration, improve production yield, and reduce manufacturing costs.

[0047] In some embodiments, the common-mode negative feedback network includes a common-mode feedback resistor and a high-frequency compensation capacitor connected in parallel. The common-mode negative feedback network provides a low-impedance path for the common-mode signal of the two amplification paths and presents a high impedance for the differential-mode signal.

[0048] This embodiment optimizes the common-mode rejection capability of the differential transistor amplifier module 20. The core solution is to address the problems of poor high-frequency common-mode rejection capability and insufficient suppression of radio frequency interference and switching power supply noise in the existing differential amplifier circuit 100. By setting a common-mode feedback resistor and a high-frequency compensation capacitor in parallel between the emitters of the two amplification paths, a wideband common-mode negative feedback network is constructed to achieve strong common-mode interference suppression across the entire frequency band from low frequency to high frequency.

[0049] A common-mode negative feedback network is set between the emitters of the two symmetrical amplification paths in the differential transistor amplifier module 20. This network consists of a common-mode feedback resistor R14 connected in parallel with a high-frequency compensation capacitor C7. For common-mode signals synchronously injected into the two input terminals (including 50 / 60Hz power frequency interference, power supply ripple, spatially coupled RF noise, etc.), this network exhibits extremely low impedance: low-frequency common-mode signals form a low-impedance path through R14, forcing the emitter voltage of the two transistors to synchronously follow the base common-mode voltage change, so that the collector current of the two transistors hardly changes synchronously, thus achieving strong suppression of common-mode signals in the first stage of amplification; under high-frequency common-mode signals, the capacitive reactance of C7 decreases significantly with increasing frequency, forming an even lower impedance path with R14, further enhancing the suppression capability of high-frequency common-mode signals, and solving the problem of the sharp drop in common-mode rejection ratio at high frequencies in traditional instrumentation amplifiers.

[0050] For the two inversely phased useful differential audio signals, the network exhibits high impedance, hardly attenuating the differential signal, and does not affect the normal amplification and gain of the differential signal, ensuring high-fidelity amplification of the useful audio signal by the circuit.

[0051] In some embodiments, the emitters of the two amplification paths of the differential transistor amplifier module 20 are grounded through independent emitter resistors to form local current negative feedback for improving the linearity of signal amplification.

[0052] This embodiment optimizes the linearity and distortion of the differential amplifier circuit 100. The core solution is to address the harmonic distortion and intermodulation distortion caused by the nonlinear transmission characteristics during transistor amplification. By configuring independent emitter grounding resistors for each of the two amplification paths, local current negative feedback is formed, which significantly improves the linearity of signal amplification, reduces nonlinear distortion, and enhances audio fidelity.

[0053] The emitter of the first transistor in the differential transistor amplifier module 20 is grounded through an independent emitter resistor R15, and the emitter of the second transistor is grounded through an independent emitter resistor R16. The parameters of the two resistors are strictly matched to construct local current negative feedback loops for the corresponding amplification paths.

[0054] During transistor amplification, when the base input signal voltage increases, leading to an increase in the transistor emitter current, the voltage drop across the emitter resistor also increases synchronously, causing the transistor emitter voltage to rise. This reduces the effective input voltage between the base and emitter, suppressing excessive growth of the emitter current. Conversely, when the base input signal voltage decreases, the negative feedback loop suppresses excessive reduction in the emitter current. Through this local current negative feedback, the linear operating range of the transistor can be effectively widened, offsetting the nonlinear region in the transistor's transfer characteristics. This significantly reduces harmonic distortion and intermodulation distortion during amplification, while also improving the circuit's gain stability. It avoids distortion problems when large dynamic range signals are input, ensuring the naturalness and fidelity of the audio signal, making it particularly suitable for recording scenarios with extremely high linearity requirements, such as vocals and acoustic instruments.

[0055] In some embodiments, the input signal receiving and DC biasing module 10 includes two symmetrically arranged input matching units. The two differential input audio signals are respectively connected to the two input terminals of the differential transistor amplifier module 20 through the corresponding input matching units, and a reference voltage unit for DC biasing is provided for the differential transistor amplifier module 20. The signal is synchronously injected into the corresponding input terminal through the two input matching units.

[0056] This embodiment optimizes the coupling and bias injection methods of the input signal, and solves the differential misalignment problem caused by mutual interference between AC signal coupling and DC bias and asymmetric bias injection in existing circuits. Through two symmetrical input matching units, synchronous access of differential signals and symmetrical injection of DC bias are achieved, while impedance matching, current limiting protection and low-frequency filtering are completed.

[0057] The input signal receiving and DC biasing module 10 is configured with two completely symmetrical input matching units, which correspond to the in-phase input IN_P and the in-phase input IN_N of the differential audio signal, respectively. The core of the first input matching unit is resistor R1, and the second is resistor R4. The parameters of the two resistors are strictly matched.

[0058] The two differential audio signals IN_P and IN_N output from the microphone are connected to the base input terminals of the two transistors in the differential transistor amplifier module 20 via resistors R1 and R4, respectively. Simultaneously, the first reference voltage unit VREF1, which provides DC bias to the differential transistor amplifier module 20, is injected synchronously into the base of the first transistor via R1 and into the base of the second transistor via R4. This ensures that the voltage at the base nodes of the two transistors is the DC bias of VREF1 superimposed on the corresponding input AC differential signal, achieving a single resistor that performs AC signal coupling, DC bias injection, and impedance matching in one function. This symmetrical injection method ensures that the DC bias of the two amplification paths is completely consistent, avoiding differential misalignment caused by bias asymmetry. Furthermore, R1 and R4 provide input current limiting protection, preventing surge signals from damaging subsequent transistors. Together with the microphone's output capacitor, they form a high-pass filter network to filter out ultra-low frequency unwanted signals and optimize the circuit's low-frequency response characteristics.

[0059] In some embodiments, the cross-feedback network module 40 includes two symmetrically arranged AC coupling units. The inverting output terminal of the fully differential operational amplifier module 30 is connected to its non-inverting input terminal via the first AC coupling unit, and the non-inverting output terminal is connected to its inverting input terminal via the second AC coupling unit, thus forming a cross-coupled AC differential negative feedback loop.

[0060] This embodiment optimizes the gain stability and frequency response of a fully differential operational amplifier. It addresses the issues of gain fluctuation and uneven frequency response across the entire audio frequency band in traditional negative feedback architectures by constructing an AC differential negative feedback loop through cross-coupled AC coupling units. This stabilizes the AC gain of the circuit, optimizes the frequency response across the entire audio frequency band, and improves the stability and anti-interference capability of the circuit.

[0061] The cross-feedback network module 40 is configured with two symmetrical AC coupling units. The first AC coupling unit is a high-precision DC blocking capacitor C1, and the second AC coupling unit is a high-precision DC blocking capacitor C8. The parameters of the two capacitors are strictly matched. The inverting output terminal OUT_P of the fully differential operational amplifier U1 is connected to the non-inverting input terminal of U1 via the first AC coupling unit C1; the non-inverting output terminal OUT_N of U1 is connected to the inverting input terminal of U1 via the second AC coupling unit C8, forming a cross-coupled AC differential negative feedback loop.

[0062] When gain fluctuations or unexpected interference occur at the circuit output, such as an unexpected increase in the voltage at the inverting output terminal OUT_P of U1, this change is coupled to the non-inverting input terminal of U1 via C1, causing the voltage at the non-inverting input terminal to rise synchronously. In response to this change, U1 lowers the voltage at the non-inverting output terminal OUT_N. Simultaneously, the differential amplification effect causes the voltage at the inverting output terminal OUT_P to decrease. The decrease in the voltage at OUT_N, in turn, is coupled to the inverting input terminal of U1 via C8, further lowering the voltage at the inverting input terminal and prompting U1 to adjust its output, thus offsetting the initial voltage fluctuations and interference. This cross-differential negative feedback loop effectively stabilizes the AC gain of the circuit, ensuring the flatness of the gain response across the entire 20Hz-20kHz frequency range, while also improving the circuit's anti-interference capability and operational stability, and avoiding the risk of self-oscillation.

[0063] In some embodiments, the non-inverting input and inverting input of the fully differential operational amplifier module 30 are grounded through independent grounding resistors to provide a DC path for the input bias current of the operational amplifier. The grounding resistors and the corresponding AC coupling units cooperate to form a high-pass filter network.

[0064] This embodiment optimizes the input bias management and low-frequency response control of a fully differential operational amplifier. The core solution addresses the problems of DC offset and uncontrollable low-frequency cutoff frequency caused by charge accumulation of the operational amplifier's input bias current. By configuring independent grounding resistors for the two input terminals of the operational amplifier, a DC path is provided for the bias current. At the same time, it works with the AC coupling unit to form a high-pass filter network, accurately setting the low-frequency cutoff frequency of the circuit.

[0065] The non-inverting input of the fully differential operational amplifier U1 is directly grounded through an independent high-precision grounding resistor R9; the inverting input of U1 is directly grounded through an independent high-precision grounding resistor R13, and the parameters of R9 and R13 are strictly matched.

[0066] The two grounding resistors provide a stable DC path for the input bias current of the input stage transistors inside U1, preventing the input voltage drift and increased DC offset caused by the continuous accumulation of bias current on the input capacitors, thus ensuring the stability of the operational amplifier's operating point. Simultaneously, grounding resistor R9, in conjunction with the first AC coupling capacitor C1 in the cross-feedback network, forms a first-order RC high-pass filter network; grounding resistor R13, in conjunction with the second AC coupling capacitor C8, forms another first-order RC high-pass filter network with completely symmetrical parameters. By matching the parameters of C1, C8, R9, and R13, the low-frequency cutoff frequency of the circuit can be precisely set, allowing the circuit to amplify only effective audio signals above 20Hz, effectively filtering out unwanted signals such as ultra-low frequency vibration noise and low-frequency power supply ripple below 20Hz, while ensuring completely symmetrical low-frequency responses of the two differential paths and avoiding differential phase distortion.

[0067] In some embodiments, the fully differential operational amplifier module 30 is provided with a common-mode voltage control terminal, which is used to set the reference voltage unit of the output common-mode level. The reference voltage unit is connected to the common-mode voltage control terminal, and the common-mode level of the two differential output terminals is locked through the common-mode feedback loop inside the operational amplifier.

[0068] This embodiment optimizes the output level matching and common-mode level control of the amplifier circuit. It solves the problems of uncontrollable output common-mode level, poor compatibility with the subsequent ADC, and low dynamic range utilization in existing circuits. By connecting an independent reference voltage unit to the common-mode voltage control terminal of the fully differential operational amplifier, and utilizing the common-mode feedback loop inside the operational amplifier, the common-mode level of the output differential signal is accurately locked, perfectly matching the input requirements of the subsequent ADC.

[0069] The fully differential operational amplifier module 30 uses a fully differential operational amplifier U1 with a built-in common-mode feedback loop. U1 has a dedicated common-mode voltage control terminal VOCM. The second reference voltage unit VREF2 in the power supply and reference voltage module 50, which is used to set the output common-mode level, is directly connected to this VOCM pin. VREF2 is generated by a high-precision, low-temperature-drift voltage reference source and can be flexibly adjusted according to the input common-mode voltage range of the subsequent ADC.

[0070] During circuit operation, the common-mode feedback loop inside U1 continuously monitors the average voltage (i.e., the output common-mode voltage) of the two differential output terminals OUT_P and OUT_N. This average voltage is compared with the VREF2 reference voltage input to the VOCM pin. The negative feedback loop forces the output common-mode voltage to strictly follow VREF2, unaffected by input signal amplitude, load changes, or temperature drift. This design allows for precise setting of the DC common-mode level of the circuit's output signal, ensuring the dynamic range of the output signal perfectly matches the optimal input range of the subsequent ADC. This maximizes the utilization of the ADC's dynamic range, avoids clipping distortion caused by signal peaks exceeding the ADC's input range, and prevents insufficient signal-to-noise ratio due to excessively small signal amplitude. This significantly improves the circuit's compatibility with different specifications of subsequent circuits.

[0071] In some embodiments, the output signal processing module 60 includes two symmetrically arranged DC blocking coupling units. The two differential output signals of the fully differential operational amplifier module 30 are output through the corresponding DC blocking coupling units, blocking the DC component and outputting a pure AC differential audio signal.

[0072] This embodiment optimizes the purity of the amplifier circuit's output signal, focusing on solving the problem of DC component interference in the output signal affecting the subsequent circuit and dynamic range. Through two symmetrical DC blocking coupling units, the DC component of the amplifier circuit output is completely blocked, outputting only a pure AC differential audio signal, thus ensuring the operational stability of the subsequent circuit.

[0073] The output signal processing module 60 is configured with two completely symmetrical DC blocking coupling units. The first DC blocking coupling unit is a high-precision DC blocking capacitor C2, and the second DC blocking coupling unit is a high-precision DC blocking capacitor C4. The parameters of the two capacitors are strictly matched. The inverting output terminal OUT_P of the fully differential operational amplifier U1 is connected to the final non-inverting output terminal OUT_P of the entire amplifier circuit via C2; the non-inverting output terminal OUT_N of U1 is connected to the final inverting output terminal OUT_N of the entire amplifier circuit via C4.

[0074] C2 and C4 are high-stability, low-leakage-current film capacitors with excellent low-frequency response characteristics. They can effectively pass AC differential signals across the entire audio frequency range of 20Hz-20kHz, while completely blocking the DC common-mode voltage set by VREF2 at the output of U1. This prevents DC components from being transmitted to the subsequent ADC or audio processing circuits, thus preventing DC components from causing operating point offset, saturation distortion, or even component damage in the subsequent circuits. Through this symmetrical DC blocking design, the final output of the two differential signals has no DC components, retaining only the pure amplified AC audio signal, ensuring the operational stability of the subsequent circuits and the fidelity of the audio signal.

[0075] In some embodiments, such as Figure 2 As shown, this embodiment addresses the core pain points of existing desktop microphone preamplifier circuits in complex desktop electromagnetic environments: excessively high background noise when amplifying weak audio signals at the microvolt level, insufficient suppression capability of common-mode interference from power frequency / switching power supply / RF (especially the common-mode rejection ratio drops sharply in the high-frequency band), high nonlinear distortion of signal amplification, unstable operating point due to temperature drift, and poor adaptability with the subsequent ADC level. It provides a two-stage audio differential amplifier circuit 100 with a fully differential symmetrical architecture.

[0076] This embodiment employs a two-stage architecture: a paired integrated dual NPN transistor preamplifier and a high-performance fully differential operational amplifier main amplifier. It is complemented by an emitter-parallel RC common-mode negative feedback network, a cross-coupled AC differential negative feedback loop, and a dual independent precision reference voltage biasing system. This achieves low-noise, high-linearity, and high anti-interference amplification of weak differential microphone signals. Through this circuit design, extremely low equivalent input noise, ultra-high wideband common-mode rejection ratio, and extremely low harmonic distortion can be achieved across the entire 20Hz-20kHz audio frequency range. It also exhibits excellent temperature stability and mass production consistency, perfectly meeting the high-fidelity audio acquisition requirements of high-end desktop microphones in complex electromagnetic environments surrounding computers.

[0077] The differential amplifier circuit 100 in this embodiment adopts a fully symmetrical differential architecture. Its core components include seven major parts: an input signal receiving and DC biasing module 10, a differential transistor amplifier module 20, a common-mode negative feedback network, a fully differential operational amplifier module 30, a cross-feedback network module 40, an output signal processing module 60, and a power supply and reference voltage module 50. The circuit connection, component configuration, and operational details of each module strictly correspond to the circuit diagram in the attached figure.

[0078] The power supply and reference voltage module 50 provides a stable power supply and two independent precision reference voltages for the entire circuit, which is the foundation for stable circuit operation. The power supply VCC provides global power to the circuit and is connected to the collector load resistor of the differential transistor amplifier module 20 and the positive power supply pin VDD of the fully differential operational amplifier U1. The negative power supply pin VEE of the fully differential operational amplifier U1 is directly grounded to GND, and the enable pin EN is grounded by default (the enable circuit works normally and can also be started and stopped by an external high / low level control circuit).

[0079] The first reference voltage source VREF1 is used to provide symmetrical DC bias for the pre-differential amplifier stage; the second reference voltage source VREF2 is connected to the common-mode voltage control pin VOCM of the fully differential operational amplifier U1, and is used to precisely lock the common-mode level of the circuit output. The two reference voltages can be adjusted independently to adapt to the level requirements of the front-end microphone and the back-end ADC respectively.

[0080] This module is the signal input interface of the circuit, realizing impedance matching, current limiting protection and symmetrical DC bias injection of microphone differential signals, corresponding to the input terminals IN_P, IN_N and the matching resistors R1, R4 in the attached diagram.

[0081] The circuit is configured with two completely symmetrical input paths: the positive differential audio signal IN_P output from the desktop microphone is directly connected to the base (pin 2) of the left differential transistor pair Q4; the negative differential audio signal IN_N output from the microphone is directly connected to the base (pin 7) of the right transistor Q4.

[0082] The first reference voltage source VREF1 is connected to the common node of IN_P and Q4 pin 2 via resistor R1. At the same time, VREF1 is connected to the common node of IN_N and Q4 pin 7 via matching resistor R4 of the same specification, realizing symmetrical injection of DC bias, so that the bases of the two transistors of Q4 obtain completely consistent DC operating points. At the same time, the input AC differential signal is superimposed to ensure the symmetry of differential amplification.

[0083] R1 and R4 are precision-matched resistors with the same precision and resistance value. On the one hand, they provide impedance matching and input current limiting protection for the microphone input signal, and together with the microphone output capacitor, they form a high-pass filter network to optimize the low-frequency response of the circuit. On the other hand, they ensure the consistency of the two bias injections and avoid differential misalignment.

[0084] The differential transistor amplifier module 20 is the core of the pre-amplification of the circuit. It uses integrated paired transistors to construct a fully symmetrical common-emitter differential amplifier circuit 100 to achieve low-noise pre-amplification of weak signals. At the same time, it improves linearity through local negative feedback, corresponding to the paired transistor Q4, collector load resistors R2 and R3, and emitter resistors R15 and R16 in the attached figure.

[0085] The core amplification device uses a pair of paired dual NPN transistors Q4 integrated in the same package. The two transistors are manufactured on the same wafer, share the same package thermal environment, and have perfectly matched electrical parameters (emitter-junction voltage drop Vbe, current amplification factor β, temperature coefficient, and noise characteristics), forming two completely symmetrical common-emitter amplification paths.

[0086] The collector (pin 1) of the left Q4 transistor is connected to the power supply VCC via a precision matching resistor R2, and the emitter (pin 3) is grounded to GND via a precision matching resistor R15. The collector (pin 8) of the right Q4 transistor is connected to VCC via a precision matching resistor R3 of the same specification as R2, and the emitter (pin 6) is grounded to GND via a precision matching resistor R16 of the same specification as R15.

[0087] During operation, the differential voltage signals from the two base inputs are amplified by the transistor current and converted into collector current changes. Then, they are converted into differential voltage signals by R2 and R3 and output to the subsequent fully differential operational amplifier module 30. R15 and R16 provide local current negative feedback for the two amplification paths, suppressing the nonlinearity of the transistor transfer characteristics, greatly improving the amplification linearity, reducing harmonic distortion, and improving gain stability.

[0088] The common-mode negative feedback network is connected between the emitters of the two amplification paths of the differential transistor amplifier module 20. The core function is to strongly suppress wideband common-mode interference, corresponding to the high-frequency compensation capacitor C7 and the common-mode feedback resistor R14 connected in parallel between the two emitters of Q4 in the attached figure.

[0089] A common-mode feedback resistor R14 and a high-frequency compensation capacitor C7 are connected in parallel between the emitter of the left transistor (pin 3) and the emitter of the right transistor (pin 6) of Q4 to form an RC common-mode negative feedback network.

[0090] For common-mode interference signals with synchronous input IN_P and IN_N (including 50 / 60Hz power frequency interference, USB switching power supply ripple, Wi-Fi / Bluetooth RF coupling noise, etc.), the base voltages of the two transistors change in phase. R14 and C7 present extremely low impedance to the common-mode signal, forcing the emitter voltages of the two transistors to synchronously follow the base voltage change, so that the collector currents of the two transistors have almost no common-mode change, thus achieving deep suppression of common-mode interference in the pre-amplification stage. For differential-mode useful audio signals with inverse phase change, the network presents high impedance, hardly attenuating the differential-mode signal and not affecting the amplification gain of the circuit.

[0091] Among them, capacitor C7 provides a lower impedance path for high-frequency common-mode signals, which greatly improves the common-mode rejection capability of the circuit in the high-frequency range and solves the problem of the sharp drop in common-mode rejection ratio at high frequencies in traditional amplifier circuits.

[0092] The fully differential operational amplifier module 30 is the main amplification core of the circuit. It performs high-gain, high-common-mode rejection ratio amplification on the pre-amplified differential signal, while accurately locking the output common-mode level to adapt to the input requirements of the subsequent ADC, corresponding to the fully differential operational amplifier U1 in the attached figure.

[0093] The non-inverting input terminal IN+ of U1 is directly connected to the common node of the collector of the left transistor of Q4 (pin 1) and R2, and the inverting input terminal IN- of U1 is directly connected to the common node of the collector of the right transistor of Q4 (pin 8) and R3, receiving the differential voltage signal after pre-amplification.

[0094] The common-mode voltage control pin VOCM of U1 is connected to the second reference voltage source VREF2. Through the common-mode feedback loop inside U1, the average voltage of the two output terminals of U1 (i.e., the output common-mode voltage) is strictly equal to VREF2 in real time. It is not affected by the input signal amplitude, load change, or temperature drift. It accurately matches the input common-mode voltage range of the subsequent ADC, maximizes the utilization of the ADC's dynamic range, and avoids clipping distortion.

[0095] The U1 is configured with two differential output terminals, an inverting output terminal and a non-inverting output terminal, to output two amplified differential audio signals with opposite phases and equal amplitudes, thus completing the main signal amplification process.

[0096] The cross-feedback network module 40 is connected between the differential output and differential input of U1 to construct a cross-coupled AC differential negative feedback loop, which stabilizes the AC gain of the circuit, optimizes the frequency response, and sets the low-frequency cutoff frequency, corresponding to the DC blocking capacitors C1 and C8 and the grounding resistors R9 and R13 in the attached figure.

[0097] The inverting output of U1 is connected to the non-inverting input IN+ via a precision-matched DC blocking capacitor C1, and the non-inverting output of U1 is connected to the inverting input IN- via a precision-matched DC blocking capacitor C8 of the same specification as C1, forming a cross-coupled AC differential negative feedback loop. This loop can effectively suppress gain fluctuations and output interference, stabilize the AC gain across the entire audio frequency range, ensure the flatness of the gain response within 20Hz-20kHz, and improve circuit stability, avoiding the risk of self-oscillation under capacitive loads.

[0098] The non-inverting input terminal IN+ of U1 is grounded to GND via a precision matching grounding resistor R9, and the inverting input terminal IN- of U1 is grounded to GND via a precision matching grounding resistor R13 of the same specification as R9. R9 and R13 provide a DC path for the input bias current of U1, avoiding input voltage drift and DC offset caused by charge accumulation. On the other hand, R9 and C1, and R13 and C8 respectively form two completely symmetrical RC high-pass filter networks. By matching the parameters of the capacitors and resistors, the low-frequency cutoff frequency of the circuit can be accurately set, effectively filtering out ultra-low frequency vibration noise and low-frequency power supply ripple below 20Hz.

[0099] The output signal processing module 60 is the output stage of the circuit, which realizes DC blocking coupling of the amplified signal and outputs a pure AC differential audio signal, corresponding to the DC blocking capacitors C2 and C4 in the attached figure and the final output terminals OUT_P and OUT_N.

[0100] The module is configured with two completely symmetrical DC blocking output paths: the inverting output terminal of U1 is connected to the final non-inverting output terminal OUT_P of the circuit via a low-leakage-current precision film capacitor C2; the non-inverting output terminal of U1 is connected to the final inverting output terminal OUT_N of the circuit via a precision film capacitor C4 of the same specification as C2.

[0101] C2 and C4 can completely block the DC common-mode voltage set by VREF2 at the output of U1, allowing only the AC differential signal in the full audio frequency band of 20Hz-20kHz to pass through. The final output is a pure amplified audio differential signal without DC components, which is directly sent to the subsequent ADC or audio processing circuit, avoiding the problem of DC components causing the operating point of the subsequent circuit to shift or saturation distortion.

[0102] When the microphone output IN_P increases positively and IN_N decreases negatively, IN_P, through R1, increases the base voltage of the left transistor Q4, increasing the collector current of the left transistor. This increases the voltage drop across R2, causing the collector voltage of the left transistor to decrease in the reverse direction. Simultaneously, IN_N, through R4, decreases the base voltage of the right transistor Q4, decreasing the collector current of the right transistor. This decreases the voltage drop across R3, causing the collector voltage of the right transistor to increase in the reverse direction. This differential voltage signal is input to the two input terminals of U1. After being amplified by U1, the voltage at the inverting output terminal of U1 decreases, and the voltage at the non-inverting output terminal increases. Finally, after DC blocking by C2 and C4, OUT_P outputs a negatively amplified AC signal, and OUT_N outputs a positively amplified AC signal, completing the low-noise, high-fidelity amplification of the weak differential audio signal.

[0103] For common-mode interference signals injected synchronously into IN_P and IN_N, the first stage of deep suppression is achieved through the common-mode negative feedback network between the emitters of Q4. The residual common-mode signal is attenuated in the second stage through the high common-mode rejection ratio of U1, and finally almost completely eliminated at the output, ensuring the circuit's anti-interference capability in complex desktop electromagnetic environments.

[0104] like Figure 3 As shown, this application provides a desktop microphone 1000, including a microphone body 200 and a differential amplifier circuit 100 provided in any embodiment of this application. The differential amplifier circuit 100 may include...

[0105] It should be noted that the desktop microphone 1000 can be a wired microphone or a wireless microphone, and this application embodiment does not limit this.

[0106] It should be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. It should be understood that when an element or layer is referred to as “on,” “adjacent to,” “connected to,” or “coupled to” other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as “directly on,” “directly adjacent to,” “directly connected to,” or “directly coupled to” other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are merely used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this application, the first element, component, area, layer, or portion discussed below may be referred to as a second element, component, area, layer, or portion.

[0107] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below,” “under,” or “below” other elements or features will be oriented “above” other elements or features. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0108] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0109] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0110] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A differential amplifier circuit for amplifying differential audio signals from a desktop microphone, characterized in that, It includes an input signal receiving and DC biasing module, a differential transistor amplification module, a fully differential operational amplifier module, a cross feedback network module, a power supply and reference voltage module, and an output signal processing module connected in sequence. The differential transistor amplifier module has a common-mode negative feedback network between the emitters of the two corresponding symmetrical amplification paths for suppressing common-mode signals. The fully differential operational amplifier module is provided with a cross-feedback network module between its differential output terminal and differential input terminal to form an AC differential negative feedback loop. The power supply and reference voltage module includes at least two reference voltage units, which provide DC bias for the differential transistor amplifier module and set the output common-mode level for the fully differential operational amplifier module, respectively.

2. The differential amplifier circuit according to claim 1, characterized in that, The two symmetrical amplification paths of the differential transistor amplification module are composed of paired bipolar transistor pairs integrated in the same package, and the two transistors have matched temperature characteristics and electrical parameters.

3. The differential amplifier circuit according to claim 2, characterized in that, The common-mode negative feedback network includes a common-mode feedback resistor and a high-frequency compensation capacitor connected in parallel. The common-mode negative feedback network provides a low-impedance path for the common-mode signal of the two amplification paths and presents a high impedance for the differential-mode signal.

4. The differential amplifier circuit according to claim 3, characterized in that, The emitters of the two amplification paths of the differential transistor amplifier module are grounded through independent emitter resistors, forming local current negative feedback to improve the linearity of signal amplification.

5. The differential amplifier circuit according to claim 1, characterized in that, The input signal receiving and DC biasing module includes two symmetrically arranged input matching units. The two differential input audio signals are respectively connected to the two input terminals of the differential transistor amplifier module through the corresponding input matching units, providing a reference voltage unit for DC biasing of the differential transistor amplifier module, and are synchronously injected into the corresponding input terminals through the two input matching units.

6. The differential amplifier circuit according to claim 1, characterized in that, The cross-feedback network module includes two symmetrically arranged AC coupling units. The inverting output of the fully differential operational amplifier module is connected to its non-inverting input via the first AC coupling unit, and the non-inverting output is connected to its inverting input via the second AC coupling unit, forming a cross-coupled AC differential negative feedback loop.

7. The differential amplifier circuit according to claim 6, characterized in that, The non-inverting and inverting input terminals of the fully differential operational amplifier module are grounded through independent grounding resistors to provide a DC path for the input bias current of the operational amplifier. The grounding resistors, together with the corresponding AC coupling units, form a high-pass filter network.

8. The differential amplifier circuit according to claim 1, characterized in that, The fully differential operational amplifier module is provided with a common-mode voltage control terminal. A reference voltage unit for setting the output common-mode level is connected to the common-mode voltage control terminal, and the common-mode level of the two differential output terminals is locked through the common-mode feedback loop inside the operational amplifier.

9. The differential amplifier circuit according to claim 1, characterized in that, The output signal processing module includes two symmetrically arranged DC blocking coupling units. The two differential output signals of the fully differential operational amplifier module are output through the corresponding DC blocking coupling units, blocking the DC component and outputting a pure AC differential audio signal.

10. A desktop microphone, characterized in that, It includes a microphone body and a differential amplifier circuit as described in any one of claims 1 to 9.

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