AM modulation circuit for CB vehicle intercom
By employing an AM modulation circuit structure using DC-DC circuits and N-channel MOS transistors in the CB vehicle-mounted walkie-talkie, the problems of large size and high cost of traditional CB vehicle-mounted walkie-talkies are solved, achieving a miniaturized and low-cost AM modulation circuit design.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- QUANZHOU XINWEI ELECTRONICS
- Filing Date
- 2025-05-16
- Publication Date
- 2026-06-16
AI Technical Summary
Traditional CB vehicle-mounted walkie-talkies suffer from large transformer size or high power consumption of the AM collector modulation circuit, making it difficult to miniaturize the device and resulting in high cost and complex heat dissipation design.
A DC-DC circuit is used to replace the traditional modulation method. The drain of the power transistor is connected to the voltage output terminal of the DC-DC circuit. The output voltage is adjusted by the DC-DC circuit to perform AM modulation. Combined with the optimization of the input-output matching circuit, an N-channel MOSFET and an IC chip are used.
This invention enables miniaturization of the AM modulation circuit, reducing heat generation and production costs, while improving circuit efficiency and reducing heat dissipation requirements.
Smart Images
Figure CN224367827U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to a walkie-talkie, and more specifically to an AM modulation circuit for a CB vehicle-mounted walkie-talkie. Background Technology
[0002] The CB vehicle-mounted radio is a short-range wireless communication device, commonly used in vehicle fleets, outdoor activities, or temporary network communication.
[0003] Traditional CB vehicle-mounted radios contain an AM collector modulation circuit, which is widely used in the transmitters of CB vehicle-mounted radios with high output power. The modulation signal output by the AM collector modulation circuit is loaded onto the drain of the power transistor. That is, the modulation signal is usually loaded onto the drain of the power transistor through a transformer coupling or a modulation tube circuit. However, when using a transformer coupling method, the transformer is large due to the large size of the transformer for higher power, which is not conducive to the miniaturization design of CB vehicle-mounted radios. Therefore, the size and power of the CB vehicle-mounted radio are limited by the transformer. When using a modulation tube circuit, the power consumption of the modulation tube itself (such as a series modulation tube) will reduce the overall efficiency, so heat dissipation design is required. In addition, the modulation tube needs to be equipped with external bias circuits and protection circuits (such as overvoltage and / or overcurrent protection circuits), which increases the cost.
[0004] In view of this, this application has conducted in-depth research on this basis, resulting in this case. Utility Model Content
[0005] The purpose of this invention is to provide a small, low-cost, and heat-reducing AM-modulated CB vehicle-mounted walkie-talkie.
[0006] To achieve the above objectives, the solution of this utility model is:
[0007] An AM modulation circuit for a CB vehicle-mounted walkie-talkie is disclosed, suitable for use in the walkie-talkie body. The walkie-talkie body includes an antenna, a low-pass filter, a carrier circuit, and a voice modulation unit for generating a modulation signal. The AM modulation circuit includes a DC-DC circuit, an input matching circuit, an output matching circuit, and a power transistor. The carrier signal terminal of the carrier circuit is connected to the gate of the power transistor through the input matching circuit. The drain of the power transistor is connected to the signal input terminal of the low-pass filter through the output matching circuit. The signal output terminal of the low-pass filter is connected to the antenna. The source of the power transistor is grounded. The DC-DC circuit has a Vout terminal, an FB terminal, and a Vin terminal. The drain of the power transistor is also connected to the Vout terminal. The Vin terminal is connected to the VCC terminal in the walkie-talkie body. The signal output terminal of the voice modulation unit is connected to the FB terminal.
[0008] The input matching circuit includes capacitors C1, C2, and C3, as well as inductor L1 and resistor R1. The carrier signal terminal of the carrier circuit is connected to the first terminal of capacitor C1. The second terminal of capacitor C1 branches into two paths: the first path is connected to the first terminal of resistor R1 through inductor L1, and the second path is grounded through capacitor C2. The second terminal of resistor R1 branches into two paths: the first path is grounded through capacitor C3, and the second path is connected to the gate of the power transistor.
[0009] The output matching circuit includes capacitors C4, C5, and C6, as well as inductors L3 and L4. The drain of the power transistor is split into two paths. The first path is connected to the first terminal of capacitor C5 through inductor L3, and the second path is grounded through capacitor C4. The second terminal of capacitor C5 is connected to the first terminal of capacitor C6 and the first terminal of inductor L4, respectively. The second terminal of capacitor C6 is grounded, and the second terminal of inductor L4 is connected to the signal output terminal of the low-pass filter.
[0010] The DC-DC circuit also has an SW terminal, which is connected to the first terminal of inductor L0. The second terminal of inductor L0 is connected to the drain of the power transistor through inductor L2, and the Vout terminal is connected to the second terminal of inductor L0.
[0011] The power transistor is an N-channel MOSFET.
[0012] The voice modulation unit includes a microphone and another low-pass filter. The microphone is connected to the signal input terminal of the low-pass filter, and the signal output terminal of the low-pass filter is connected to the FB terminal of the DC-DC circuit.
[0013] With the above structure, this utility model has the following beneficial effects: The drain of the power transistor is connected to the voltage output terminal (Vout terminal) of the DC-DC circuit, and the modulation signal is loaded to the feedback terminal (i.e., FB terminal) of the DC-DC circuit. The output voltage is adjusted by the DC-DC circuit to achieve the modulation of the AM modulation signal. Compared with the prior art, the use of the DC-DC circuit for AM modulation results in a smaller PCB board in the walkie-talkie body due to the small size of the DC-DC circuit, which enables the miniaturization design of the AM modulation circuit. This reduces the space occupation rate of the AM modulation circuit. The DC-DC circuit has higher efficiency, which reduces the heat generation of the AM modulation circuit and reduces the heat dissipation requirements. Furthermore, since the AM modulation circuit only requires one IC and some external auxiliary resistors, capacitors, and inductors, the production cost is lower. Attached Figure Description
[0014] Figure 1 This is a structural block diagram of the present invention.
[0015] Figure 2 This is the circuit schematic diagram of this utility model. Detailed Implementation
[0016] To further explain the technical solution of this utility model, the following detailed description is provided through specific embodiments.
[0017] An AM modulation circuit for a CB vehicle-mounted walkie-talkie is disclosed, applicable to existing conventional walkie-talkie bodies. In this embodiment, the walkie-talkie body is a conventional CB vehicle-mounted walkie-talkie. Alternatively, the walkie-talkie body can also be a conventional handheld walkie-talkie or other conventional walkie-talkie. In this embodiment, the existing walkie-talkie body includes an antenna, a carrier circuit, and a voice modulation unit. The carrier circuit is used to generate a carrier signal; wherein, the carrier circuit can be an existing carrier generation circuit already used in walkie-talkie bodies, such as a crystal oscillator or frequency synthesizer.
[0018] The aforementioned voice modulation unit can be an existing modulation signal generation unit already used in walkie-talkie bodies. For example, the voice modulation unit includes a low-pass filter and a microphone. The microphone is electrically connected to the signal input terminal of the low-pass filter. The voice signal transmitted by the microphone is amplified by conventional audio and then filtered by the low-pass filter (LPF) to form the following modulation signal (i.e., voice signal).
[0019] The improvement of this utility model is that, as Figure 1-2 As shown, the walkie-talkie body also includes an AM modulation circuit, which includes a DC-DC circuit, a low-pass filter, an input matching circuit, an output matching circuit, and a power transistor. The carrier signal output terminal of the carrier circuit is connected to the signal input terminal of the input matching circuit. The signal output terminal of the input matching circuit is connected to the gate of the power transistor G1. The source of the power transistor G1 is grounded. The drain of the power transistor G1 is connected to the signal input terminal of the output matching circuit. The signal output terminal of the output matching circuit is connected to the antenna through the low-pass filter (LPF). The DC-DC circuit has a Vout terminal, an FB terminal, and a Vin terminal. The drain of the power transistor G1 is also connected to the Vout terminal of the DC-DC circuit. The Vin terminal of the DC-DC circuit is connected to the VCC terminal in the walkie-talkie body so as to provide the operating voltage to the DC-DC circuit through the VCC terminal. The FB terminal (i.e., the feedback terminal) of the DC-DC circuit is electrically connected to the signal output terminal of the voice modulation unit so as to transmit the modulation signal generated by the voice modulation unit to the feedback terminal of the DC-DC circuit.
[0020] It should be noted that the VCC terminal in the walkie-talkie body is the conventional power supply pin in the walkie-talkie, which provides the operating voltage to the walkie-talkie body, that is, to the DC-DC circuit.
[0021] Furthermore, the aforementioned DC-DC circuit also has an SW terminal. The SW terminal of the DC-DC circuit is electrically connected to the first terminal of inductor L0, and the second terminal of inductor L0 is connected to power transistor G1 through inductor L2, which is a feed inductor. In this embodiment, the DC-DC circuit uses a commercially available BUCK step-down DC chip.
[0022] Furthermore, the aforementioned input matching circuit includes capacitors C1, C2, and C3, as well as inductor L1 and resistor R1. The carrier signal output terminal of the carrier circuit is electrically connected to the first terminal of capacitor C1. The second terminal of capacitor C1 branches into two paths: the first path connects to the first terminal of resistor R1 through inductor L1, and the second path is grounded through capacitor C2. The second terminal of resistor R1 is connected to the gate of power transistor G1 and the first terminal of capacitor C3, respectively. The second terminal of capacitor C3 is grounded. In this way, the carrier signal generated by the carrier circuit is optimized by the aforementioned input matching circuit to improve the transmission efficiency of the carrier signal, reduce reflection loss, and perform impedance matching with subsequent circuits. Then, the optimized carrier signal is transmitted to the gate of power transistor G1, which also becomes the driving terminal.
[0023] Furthermore, the aforementioned output matching circuit includes capacitors C4, C5, and C6, as well as inductors L3 and L4. The drain of power transistor G1 is connected to the first terminal of capacitor C4 and the first terminal of inductor L3, respectively. The second terminal of capacitor C4 is grounded, and the second terminal of inductor L3 is electrically connected to the first terminal of capacitor C5. The second terminal of capacitor C5 branches into two paths: one path is grounded through capacitor C6, and the other path is connected to the signal input terminal of another low-pass filter through inductor L4. The signal output terminal of this low-pass filter is connected to the antenna. In the aforementioned DC-DC circuit, the Vout terminal and the second terminal of inductor L0 are both connected to the drain of power transistor G1 through inductor L2. Thus, the modulated AM signal is optimized by first optimizing it to ensure power transmission efficiency, then filtering out harmonics and noise through a low-pass filter, and finally transmitting the optimized and filtered AM modulated signal through the antenna.
[0024] Furthermore, the power transistors mentioned above are commercially available power transistors, and in this embodiment, the power transistor is an N-channel MOSFET.
[0025] This utility model discloses an AM modulation circuit for a CB vehicle-mounted walkie-talkie. Its specific working principle is as follows: the voice modulation unit in the walkie-talkie body generates a modulation signal and transmits it to the feedback terminal (FB terminal) of the DC-DC circuit. Through adjustment by the PWM, PFM, or PSM modules in the DC-DC circuit, the output voltage from the Vout terminal of the DC-DC circuit is sent to the drain of the power transistor G1, thereby controlling the power supply voltage of the power transistor G1 and changing the amplitude of its output radio frequency signal (i.e., the AM modulation signal), thus achieving AM modulation. Simultaneously, the carrier circuit generates a carrier signal, which, after optimization by the input matching circuit, is transmitted to the gate of the power transistor G1. After amplification by the carrier signal of the power transistor G1, the modulated AM signal is further optimized by the matching output circuit, filtered by a low-pass filter, and then transmitted through the antenna.
[0026] This utility model discloses an AM modulation circuit for a CB vehicle-mounted walkie-talkie. Compared with the prior art, it uses a DC-DC circuit to modulate the voice modulation signal, requiring only one IC chip (i.e., a chip integrating a DC-DC circuit) and peripheral auxiliary resistors, capacitors, and inductors. This results in a smaller footprint when the AM modulation circuit is integrated on a PCB board, enabling miniaturized design of the AM modulation circuit, reducing space occupancy, and lowering production costs. Furthermore, the DC-DC circuit has high efficiency, and the optimization of the output and input matching circuits reduces useless energy loss during transmission, thereby reducing the heat generation of the AM modulation circuit.
[0027] The above description is only a preferred embodiment of this invention. All equivalent changes and modifications made within the scope of the claims of this utility model shall fall within the scope of the claims of this utility model.
Claims
1. An AM modulation circuit for a CB vehicle-mounted walkie-talkie, suitable for use in the walkie-talkie body, the walkie-talkie body comprising an antenna, a low-pass filter, a carrier circuit, and a voice modulation unit for generating a modulation signal; characterized in that: The AM modulation circuit includes a DC-DC circuit, an input matching circuit, an output matching circuit, and a power transistor. The carrier signal terminal of the carrier circuit is connected to the gate of the power transistor through the input matching circuit. The drain of the power transistor is connected to the signal input terminal of the low-pass filter through the output matching circuit. The signal output terminal of the low-pass filter is connected to the antenna. The source of the power transistor is grounded. The DC-DC circuit has a Vout terminal, an FB terminal, and a Vin terminal. The drain of the power transistor is also connected to the Vout terminal. The Vin terminal is connected to the VCC terminal in the walkie-talkie body. The signal output terminal of the voice modulation unit is connected to the FB terminal.
2. The AM modulation circuit of a CB vehicle-mounted walkie-talkie according to claim 1, characterized in that: The input matching circuit includes capacitors C1, C2, and C3, as well as inductor L1 and resistor R1. The carrier signal terminal of the carrier circuit is connected to the first terminal of capacitor C1. The second terminal of capacitor C1 branches into two paths: the first path is connected to the first terminal of resistor R1 through inductor L1, and the second path is grounded through capacitor C2. The second terminal of resistor R1 branches into two paths: the first path is grounded through capacitor C3, and the second path is connected to the gate of the power transistor.
3. The AM modulation circuit of a CB vehicle-mounted walkie-talkie according to claim 1 or 2, characterized in that: The output matching circuit includes capacitors C4, C5, and C6, as well as inductors L3 and L4. The drain of the power transistor is split into two paths. The first path is connected to the first terminal of capacitor C5 through inductor L3, and the second path is grounded through capacitor C4. The second terminal of capacitor C5 is connected to the first terminal of capacitor C6 and the first terminal of inductor L4, respectively. The second terminal of capacitor C6 is grounded, and the second terminal of inductor L4 is connected to the signal output terminal of the low-pass filter.
4. The AM modulation circuit of a CB vehicle-mounted walkie-talkie according to claim 3, characterized in that: The DC-DC circuit also has an SW terminal, which is connected to the first terminal of inductor L0. The second terminal of inductor L0 is connected to the drain of the power transistor through inductor L2, and the Vout terminal is connected to the second terminal of inductor L0.
5. The AM modulation circuit of a CB vehicle-mounted walkie-talkie according to any one of claims 1-3, characterized in that: The power transistor is an N-channel MOSFET.
6. The AM modulation circuit of a CB vehicle-mounted walkie-talkie according to any one of claims 1-3, characterized in that: The voice modulation unit includes a microphone and another low-pass filter. The microphone is connected to the signal input terminal of the low-pass filter, and the signal output terminal of the low-pass filter is connected to the FB terminal of the DC-DC circuit.