A low-frequency amplifier circuit

Abstract

This utility model discloses a low-frequency amplifier circuit, including a signal input unit, a first-stage amplifier unit, a second-stage amplifier unit, and a filter unit. The signal input unit, the first-stage amplifier unit, and the second-stage amplifier unit are connected together, and the filter unit is connected to both the first-stage amplifier unit and the second-stage amplifier unit. The advantages of this utility model are: by amplifying the received signal step by step through the first-stage and second-stage amplifier units, the signal frequency is avoided from being too low to be received by the receiver. At the same time, during signal transmission, the filter unit filters out signal interference, ensuring the stability and accuracy of the signal transmission process.

Description

Technical Field

[0001] This utility model relates to the field of wireless transmission communication, and more specifically to a low-frequency amplifier circuit. Background Technology

[0002] Low-frequency amplifiers typically refer to voltage amplifiers, generally used in the preamplifier stage of a system. Their load is the input resistance of the subsequent amplifier, so the load is relatively light (the load resistance is relatively large). The purpose of this type of amplifier is to amplify and condition the input signal to obtain a sufficiently large output voltage and to adjust or improve various electrical performance aspects. Therefore, in addition to voltage gain specifications, the design often considers various specifications such as noise and frequency response, while the output power requirement is relatively low (the output power is relatively small).

[0003] In a voice wireless transceiver system, the transmitter amplifies the received voice signal through multiple stages before transmitting it. The receiver receives the transmitted signal, selects the frequency, demodulates it, amplifies it again, and then reconstructs the original voice signal for output. Antennas must receive or transmit signals at their inherent frequencies; if the frequency is too low, the antenna cannot receive it. Therefore, low-frequency amplification of the received voice signal is crucial when the transmitter is used for voice transmission. A lack of low-frequency amplification circuitry will directly result in the transmitter's transmitted signal not being received by the receiver, leading to voice transmission failure. However, even if the transmitter can perform low-frequency amplification, there are still requirements for the amplified signal's anti-interference capabilities. If signals other than the voice signal are not filtered out during low-frequency amplification, signal interference will occur, causing the receiver to receive a signal mixed with too much interference, making accurate transmission impossible. Therefore, designing a circuit that can perform low-frequency amplification and effectively filter signal interference is essential for the transmitter. Utility Model Content

[0004] The technical problem to be solved by this utility model is to provide a circuit that can perform low-frequency amplification and effectively filter out signal interference, so as to ensure that the transmitted signal can be received by the receiver, and at the same time ensure the stability and accuracy of signal transmission.

[0005] This utility model solves the above-mentioned technical problems through the following technical means: a low-frequency amplifier circuit, including a signal input unit, a first-stage amplifier unit, a second-stage amplifier unit, and a filter unit, wherein the signal input unit, the first-stage amplifier unit, and the second-stage amplifier unit are connected, and the filter unit is connected to the first-stage amplifier unit and the second-stage amplifier unit respectively.

[0006] This invention receives external signals through a signal input unit, and amplifies the received signals step by step through a first-stage amplification unit and a second-stage amplification unit to avoid signals with too low a frequency that cannot be received by the receiver. At the same time, during signal transmission, a filtering unit filters out signal interference to ensure the stability and accuracy of the signal transmission process.

[0007] Furthermore, the signal input unit is a microphone MK1, the first-stage amplification unit is a transistor VT4, the second-stage amplification unit is a transistor VT5, the microphone MK1 receives the voice input signal, one end of the microphone MK1 is connected to the base of the transistor VT4, the collector of the transistor VT4 is connected to the base of the transistor VT5, the collector of the transistor VT5 serves as the first signal output terminal, and the emitter of the transistor VT4, the emitter of the transistor VT5, and the other end of the microphone MK1 are connected.

[0008] Furthermore, the filtering unit includes capacitor C1, resistor R1, capacitor C13, and resistor R9. One end of the microphone MK1 is connected to one end of capacitor C13 and one end of resistor R1, respectively. The other end of capacitor C13 is connected to one end of resistor R9 and the base of transistor VT4, respectively. The positive terminal of capacitor C1 is connected to the other end of resistor R1, and the negative terminal of capacitor C1 is grounded.

[0009] Furthermore, the filter unit also includes a resistor R2, a capacitor C14, and a resistor R10. The other end of the resistor R9, one end of the resistor R2, the collector of the transistor VT4, and one end of the capacitor C14 are connected. The other end of the capacitor C14 is connected to one end of the resistor R10 and the base of the transistor VT5, respectively. The other end of the resistor R2 is connected to the other end of the resistor R1.

[0010] Furthermore, the filtering unit also includes resistor R3, capacitor C6, resistor R4, resistor R12, capacitor C2, and capacitor C3. The other end of resistor R10, one end of resistor R3, the positive terminal of capacitor C6, and the collector of transistor VT5 are connected. The negative terminal of capacitor C6 serves as the first signal output terminal. The emitter of transistor VT5, one end of resistor R12, the emitter of transistor VT4, and the other end of microphone MK1 are connected and grounded. The other end of resistor R12 is connected to one end of resistor R4. The other ends of resistor R4 and resistor R3 are both connected to the other end of resistor R2.

[0011] Furthermore, capacitors C6, C2, and C1 are all polarized capacitors.

[0012] Furthermore, the microphone MK1 preamplifier is also connected to an amplitude modulation circuit for amplitude modulation of the input voice signal.

[0013] Furthermore, there are two amplitude modulation circuits, and the microphone MK1 receives two dual-channel voice input signals after amplitude modulation.

[0014] The advantages of this invention are as follows: This invention receives signals from the outside through a signal input unit, and amplifies the received signals step by step through a first-stage amplification unit and a second-stage amplification unit to avoid the signal frequency being too low to be received by the receiver. At the same time, during the signal transmission process, a filtering unit filters out signal interference to ensure the stability and accuracy of the signal transmission process. Attached Figure Description

[0015] Figure 1 This is a structural block diagram of the voice signal transmitter disclosed in the embodiments of this utility model;

[0016] Figure 2 This is a schematic diagram of the low-frequency amplifier circuit disclosed in the embodiments of this utility model;

[0017] Figure 3 This is a schematic diagram of the frequency synthesis oscillation circuit in the voice signal transmitter disclosed in the embodiments of this utility model;

[0018] Figure 4 This is a schematic diagram of the resonant hybrid circuit in the voice signal transmitter disclosed in the embodiments of this utility model;

[0019] Figure 5 This is a schematic diagram of the impedance matching transmission circuit in the voice signal transmitter disclosed in the embodiments of this utility model. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below in conjunction with the embodiments of this utility model. Obviously, the described embodiments are only some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0021] like Figure 1 As shown, the low-frequency amplifier circuit 1 provided by this utility model is mainly used in a voice signal transmitter. After amplifying and filtering the voice signal, it is output to the receiver for reception and reconstruction of the voice signal. The voice signal transmitter includes a low-frequency amplifier circuit 1, a frequency synthesis oscillation circuit 2, a resonant hybrid circuit 3, and an impedance matching transmitter circuit 4 connected in sequence. The low-frequency amplifier circuit 1 receives the voice input signal, and the impedance matching transmitter circuit 4 outputs a high-frequency small signal that satisfies the radiation frequency of the internal antenna of the transmitter.

[0022] like Figure 2As shown, the low-frequency amplifier circuit 1 includes capacitors C1, C2, and C3; resistors R1 to R4 numbered sequentially; microphone MK1; resistors R9, R10, and R12; capacitors C13, C14, and C6; transistor VT4; and transistor VT5. Microphone MK1 receives two amplitude-modulated dual-channel voice input signals. The front end of microphone MK1 can be connected to a 30kHz amplitude modulation circuit and a 40kHz amplitude modulation circuit. The amplitude-modulated dual-channel voice signals are then transmitted to the low-frequency amplifier circuit 1 through microphone MK1. One end of microphone MK1 is connected to one end of capacitor C13 and one end of resistor R1. The other end of capacitor C13 is connected to one end of resistor R9 and the base of transistor VT4. The other end of resistor R9 and one end of resistor R2... The collector of transistor VT4 is connected to one end of capacitor C14. The other end of capacitor C14 is connected to one end of resistor R10 and the base of transistor VT5. The other end of resistor R10, one end of resistor R3, the positive terminal of capacitor C6, and the collector of transistor VT5 are connected. The negative terminal of capacitor C6 is connected to frequency synthesis oscillation circuit 2. One end of resistor R12, the emitter of transistor VT5, the emitter of transistor VT4, and the other end of microphone MK1 are connected and grounded. The other end of resistor R12 is connected to one end of resistor R4. Resistors R1 to the other end of resistor R4, the positive terminals of capacitors C1 and C2, and one end of capacitor C3 are all connected. One end of capacitor C3 is connected to resonant mixing circuit 3. The negative terminals of capacitors C1 and C2, and the other end of capacitor C3 are grounded. Transistors VT4 and VT5 amplify the input voice signal in two stages. Resistors and capacitors form a filtering circuit to ensure the stability of signal transmission and filter out signal interference.

[0023] like Figure 3 As shown, the frequency synthesis oscillation circuit 2 includes a resistor R11, a crystal oscillator JT1, and a diode VD1. One end of the resistor R11 is connected to the negative terminal of the capacitor C6, and the other end of the resistor R11 is connected to one end of the crystal oscillator JT1 and the cathode of the diode VD1. The other end of the crystal oscillator JT1 and the anode of the diode VD1 are both connected to the resonant hybrid circuit 3. The frequency of the crystal oscillator JT1 is one-third of 48.5MHz. The frequency synthesis oscillation circuit 2 modulates two different frequencies and applies them to the dual-channel voice input signals to increase the frequency of the voice signals and facilitate signal transmission.

[0024] like Figure 4As shown, the resonant hybrid circuit 3 includes resistor R6, capacitor C4, inductor L1, resistor R7, capacitor C5, inductor L2, capacitor C7, inductor L3, transistors VT1 to VT3 numbered sequentially, capacitor C12, capacitor C15, resistors R14 to R17 numbered sequentially, capacitor C20, capacitor C21, and capacitor C22. One end of resistor R6, one end of resistor R14, one end of capacitor C15, and the base of transistor VT1 are connected and connected to the other end of crystal oscillator JT1. The collector of transistor VT1, one end of capacitor C4, one end of inductor L1, and one end of capacitor C12 are connected. The emitter of transistor VT1, the other end of capacitor C15, one end of resistor R15, and one end of capacitor C20 are connected. The other end of capacitor C12, one end of resistor R7, one end of resistor R16, and capacitor C22 are connected. One end of 21 is connected to the base of transistor VT2; the collector of transistor VT2, one end of capacitor C5, one end of inductor L2, and one end of capacitor C7 are connected; the other end of capacitor C7, one end of resistor R17, one end of capacitor C22, and the base of transistor VT3 are connected; the collector of transistor VT3 is connected to one end of inductor L3; the other ends of resistor R14, resistor R17, capacitor C20, capacitor C21, capacitor C22, and the emitter of transistor VT3 are all connected together; the other ends of resistor R6, capacitor C4, inductor L1, resistor R7, capacitor C5, inductor L2, and inductor L3 are all connected together; the other end of inductor L3 and the emitter of transistor VT3 are connected to impedance matching emitter circuit 4. Transistor VT1 and capacitor C4 form a frequency multiplier circuit to select the third frequency of the resonant hybrid circuit 3. Transistor VT2 and capacitor C5 form a class C amplifier for power amplification. Transistor VT3 and inductor L3 form a buffer amplifier circuit to further buffer and amplify the signal. In this way, the signal after step-by-step amplification can meet the radiation frequency of the antenna, so that the antenna E2 of the receiving part can receive the signal transmitted by the transmitting part. Without signal amplification, the signal is too weak. In addition, there is a certain distance between the transmitting part and the receiving part during transmission, which can easily make it difficult for the receiving part to receive the voice signal.

[0025] like Figure 5As shown, the impedance matching transmitting circuit 4 includes capacitors C8 to C11 (numbered sequentially), inductors L4, L5, and L6, resistor R8, capacitors C16 to C19 (numbered sequentially), indicator LED1, and antenna E1. One end of capacitor C8 is connected to one end of inductor L3, and the other end of capacitor C8, one end of inductor L4, and one end of capacitor C16 are connected. The other end of inductor L4 is connected to one end of capacitor C9, and the other end of capacitor C9, one end of inductor L5, and one end of capacitor C17 are connected. Inductor L5... The other end of the inductor is connected to one end of the inductor L6 and one end of the capacitor C18. The other end of the inductor L6 is connected to the antenna E1 and one end of the capacitor C19. One end of the resistor R8, the positive terminal of the capacitor C10, and one end of the capacitor C11 are all connected to the other end of the inductor L3 and connected to the +6V power supply. The other end of the resistor R8 is connected to the anode of the indicator LED1. The emitter of the transistor VT3, the other ends of capacitors C16 to C19, the cathode of the indicator LED1, the negative terminal of capacitor C10, and the other end of capacitor C11 are all connected to and grounded. The impedance matching transmitter circuit 4 filters out small signal interference through step-by-step filtering. The Π-type impedance matching network minimizes the input impedance, so that the antenna can obtain the maximum output power and greatly reduce the antenna radiation loss.

[0026] Through the above technical solutions, this utility model receives external signals through a signal input unit, and amplifies the received signals step by step through a first-stage amplification unit and a second-stage amplification unit to avoid the signal frequency being too low to be received by the receiver. At the same time, during the signal transmission process, a filtering unit filters out signal interference to ensure the stability and accuracy of the signal transmission process.

[0027] The above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A low frequency amplification circuit, characterized by, It includes a signal input unit, a first-stage amplification unit, a second-stage amplification unit, and a filtering unit. The signal input unit, the first-stage amplification unit, and the second-stage amplification unit are connected together, and the filtering unit is connected to both the first-stage amplification unit and the second-stage amplification unit. The signal input unit is a microphone MK1, the first-stage amplification unit is a transistor VT4, the second-stage amplification unit is a transistor VT5, the microphone MK1 receives the voice input signal, one end of the microphone MK1 is connected to the base of transistor VT4, the collector of transistor VT4 is connected to the base of transistor VT5, the collector of transistor VT5 serves as the first signal output terminal, and the emitter of transistor VT4, the emitter of transistor VT5, and the other end of microphone MK1 are connected. The filtering unit includes capacitor C1, resistor R1, capacitor C13 and resistor R9. One end of the microphone MK1 is connected to one end of capacitor C13 and one end of resistor R1 respectively. The other end of capacitor C13 is connected to one end of resistor R9 and the base of transistor VT4 respectively. The positive terminal of capacitor C1 is connected to the other end of resistor R1 and the negative terminal of capacitor C1 is grounded. The filter unit also includes a resistor R2, a capacitor C14 and a resistor R10. The other end of the resistor R9, one end of the resistor R2, the collector of the transistor VT4 and one end of the capacitor C14 are connected. The other end of the capacitor C14 is connected to one end of the resistor R10 and the base of the transistor VT5. The other end of the resistor R2 is connected to the other end of the resistor R1. The filtering unit also includes resistor R3, capacitor C6, resistor R4, resistor R12, capacitor C2, and capacitor C3. The other end of resistor R10, one end of resistor R3, the positive terminal of capacitor C6, and the collector of transistor VT5 are connected. The negative terminal of capacitor C6 serves as the first signal output terminal. The emitter of transistor VT5, one end of resistor R12, the emitter of transistor VT4, and the other end of microphone MK1 are connected and grounded. The other end of resistor R12 is connected to one end of resistor R4. The other ends of resistor R4 and resistor R3 are both connected to the other end of resistor R2.

2. A low frequency amplification circuit according to claim 1, characterized in that The capacitors C6, C2, and C1 are all polarized capacitors.

3. A low frequency amplification circuit according to claim 1, wherein The microphone MK1 preamplifier is also connected to an amplitude modulation circuit for modulating the input voice signal.

4. A low frequency amplification circuit according to claim 3, characterised in that There are two amplitude modulation circuits, and the microphone MK1 receives two dual-channel voice input signals after amplitude modulation.

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