External clock circuit of radio frequency integrated circuit and interference control method thereof, intercom

Abstract

This invention discloses an external clock circuit for a radio frequency integrated circuit and its interference control method, as well as a walkie-talkie. The external clock circuit of the radio frequency integrated circuit includes a first crystal oscillator path with a first crystal oscillator and a second crystal oscillator path with a second crystal oscillator. The oscillation frequencies of the first and second crystal oscillators are non-integer multiples of each other. When frequency harmonic interference exists, the operating crystal oscillator can be switched from the first to the second crystal oscillator, essentially switching to a different operating system, thus eliminating interference caused by the first crystal oscillator. Furthermore, because the operating crystal oscillator is directly switched, the voltage control range of the crystal oscillator does not need to be considered. Compared with existing technologies, conventional crystal oscillators can be selected, resulting in lower costs and easier component selection. Moreover, due to the use of a dual crystal oscillator path, it can handle frequency harmonic interference received by walkie-talkies in various frequency bands and with different bandwidths, offering wide application range and high compatibility.

Description

Technical Field

[0001] This invention relates to the field of communication technology, specifically to an external clock circuit for radio frequency integrated circuits and its interference control method, and a walkie-talkie. Background Technology

[0002] Existing walkie-talkies generally use a crystal oscillator as the frequency reference source and employ a PLL / DDS to generate the local oscillator. PLL stands for Phase-Locked Loop, and DDS is for Direct Data Frequency Synthesizer. However, when the receiving frequency is exactly equal to a harmonic of the crystal oscillator, the receiver will be interfered with by harmonic radiation from the crystal itself; this is known as harmonic interference. Traditional solutions involve increasing shielding and using low-pass filters to increase the attenuation of conducted / radiated signals to the receiver, thereby reducing interference. However, adding shielding complicates the receiver structure and increases cost, while filters theoretically only provide suppression of tens of dB. Limited by shielding or filtering performance, neither can completely solve the harmonic interference problem.

[0003] Chinese invention patent application CN113676199A discloses a solution to frequency multiplication interference caused by a receiver reference frequency source and a receiver. It solves the frequency multiplication interference problem by adjusting the clock frequency fref of the reference frequency source so that the frequency difference between the adjusted fref×N and the received frequency RFrx is greater than the channel occupied bandwidth OBW. Furthermore, it compensates for the frequency error caused by adjusting the reference frequency source, ensuring the normal operation of the receiving circuit. This completely solves the frequency multiplication interference problem caused by the receiver reference frequency source. Compared to existing solutions, it eliminates the need for radiation / conduction suppression devices such as shielding covers and low-pass filters, thus reducing costs. CN113676199A uses software to adjust the clock frequency of the reference frequency source 11. During operation, the microcontroller unit 15 adjusts the DC voltage output to the reference frequency source 11 by the digital-to-analog converter 14, thereby controlling the drive current of the temperature-compensated crystal oscillator in the reference frequency source 11, so that the frequency control port of the reference frequency source 11 outputs a clock frequency at a set adjustment ratio. In CN113676199A, the selected bias ratio is 32ppm, which means that the temperature-compensated crystal oscillator used in the reference frequency source 11 is a temperature-compensated crystal oscillator with a voltage-controlled range of 32ppm.

[0004] The voltage-controlled range (VCO) of conventional temperature-compensated crystal oscillators (TCCs) on the market is generally between 9 and 15 ppm. The TCC used in CN113676199A, with a VCO range of 32 ppm, is an unconventional device, expensive and difficult to procure. Furthermore, the receiver channel bandwidth in CN113676199A is 12.5 kHz, while common walkie-talkie channel bandwidths include narrowband bandwidths of 12.5 kHz and below, as well as midband 20 kHz and wideband 25 kHz. The method used in CN113676199A can only handle frequency harmonic interference for narrowband walkie-talkie receivers, resulting in a narrow application range and poor compatibility. To handle frequency harmonic interference for wider bandwidth walkie-talkie receivers, a TCC with a larger VCO range would be required, making it even more difficult to achieve.

[0005] On the other hand, with the widespread development of integrated circuits, single-chip RF solutions have become the mainstream application. However, besides the defect of frequency doubling interference, single-chip RF solutions also suffer from the defect of transmit sideband harmonics. Factors contributing to transmit sideband harmonics include the inherent suppression capabilities of the RF device itself, as well as the instability of the crystal oscillator. The performance of the crystal oscillator is affected by many factors, such as temperature changes, power supply fluctuations, and RF interference. These factors cause random changes in the frequency and phase of the crystal oscillator, resulting in poor frequency stability and generating significant phase noise, also known as sideband harmonics. Sideband harmonics cause spectral spread of the signal, increase signal power, reduce signal energy efficiency, and cause interference with other signals. Furthermore, when sideband harmonics are too large, the receiver may be unable to correctly identify the phase information of the signal, leading to decreased reception performance and increased bit error rate. Currently, there is no good solution for transmit sideband harmonics. Summary of the Invention

[0006] The purpose of this invention is to provide an external clock circuit for a radio frequency integrated circuit and its interference control method, as well as a walkie-talkie, which features low cost, convenient component selection, wide application range, and high compatibility.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: An interference control method for an external clock circuit of a radio frequency integrated circuit involves setting up a first crystal oscillator path with a first crystal oscillator and a second crystal oscillator path with a second crystal oscillator in the external clock circuit of the radio frequency integrated circuit of a walkie-talkie, wherein the oscillation frequency of the first crystal oscillator and the oscillation frequency of the second crystal oscillator are non-integer multiples of each other. A crystal oscillator interference comparison table is established, which records integer multiples of the oscillation frequency of the first crystal oscillator that fall within the operating frequency range of the walkie-talkie. When the operating frequency of the walkie-talkie is not in the crystal oscillator interference reference table, the first crystal oscillator path is activated, so that the radio frequency integrated circuit operates in a mode with the first crystal oscillator as the reference frequency source. When the operating frequency of the walkie-talkie is in the crystal oscillator interference reference table, the second crystal oscillator path is activated, causing the radio frequency integrated circuit to operate in a mode with the second crystal oscillator as the reference frequency source.

[0008] Furthermore, the crystal oscillator interference comparison table also records the frequency points where the sideband harmonics of the radio frequency integrated circuit do not meet the standard when operating in the first crystal oscillator path.

[0009] Furthermore, both the first crystal oscillator and the second crystal oscillator are temperature-compensated crystal oscillators.

[0010] Furthermore, the oscillation frequency of the first crystal oscillator is 19.2MHz, 20MHz, 24MHz, 25MHz, 26MHz, 38.4MHz, 40MHz, 48MHz, 50MHz or 52MHz; the oscillation frequency of the second crystal oscillator is 19.2MHz, 20MHz, 24MHz, 25MHz, 26MHz, 38.4MHz, 40MHz, 48MHz, 50MHz or 52MHz.

[0011] The external clock circuit of the radio frequency integrated circuit includes a power supply system, a microprocessor, a first crystal oscillator path, a second crystal oscillator path, a switching switch, and a third filter circuit; The power supply system provides operating power to the entire external clock circuit; The first crystal oscillator path includes a first crystal oscillator and a first filter circuit connected in sequence; The second crystal oscillator path includes a power supply switch, a second crystal oscillator, and a second filter circuit connected in sequence; The output terminal of the microprocessor is connected to the switching control terminal of the power supply switch and the switching control terminal of the switching switch, respectively. The output terminal of the switching switch is connected to the input terminal of the third filter circuit, and the output terminal of the third filter circuit provides a clock signal to the radio frequency integrated circuit of the walkie-talkie. The oscillation frequency of the first crystal oscillator and the oscillation frequency of the second crystal oscillator are non-integer multiples of each other; The microprocessor contains a crystal oscillator interference lookup table, which records integer multiples of the oscillation frequency of the first crystal oscillator that fall within the operating frequency range of the walkie-talkie. The microprocessor is configured to, when the operating frequency of the walkie-talkie is not in the crystal oscillator interference lookup table, connect the first crystal oscillator path via the switching switch, so that the radio frequency integrated circuit of the walkie-talkie operates in a mode with the first crystal oscillator as the reference frequency source; and, when the operating frequency of the walkie-talkie is in the crystal oscillator interference lookup table, connect the second crystal oscillator path via the switching switch and the power supply switch, so that the radio frequency integrated circuit operates in a mode with the second crystal oscillator as the reference frequency source.

[0012] Furthermore, the crystal oscillator interference comparison table also records the frequency points where the sideband harmonics of the radio frequency integrated circuit do not meet the standard when operating in the first crystal oscillator path.

[0013] Furthermore, both the first crystal oscillator and the second crystal oscillator are temperature-compensated crystal oscillators.

[0014] Furthermore, the oscillation frequency of the first crystal oscillator is 19.2MHz, 20MHz, 24MHz, 25MHz, 26MHz, 38.4MHz, 40MHz, 48MHz, 50MHz or 52MHz; the oscillation frequency of the second crystal oscillator is 19.2MHz, 20MHz, 24MHz, 25MHz, 26MHz, 38.4MHz, 40MHz, 48MHz, 50MHz or 52MHz.

[0015] The walkie-talkie uses the external clock circuit of the radio frequency integrated circuit as described above.

[0016] The external clock circuit of the walkie-talkie's radio frequency integrated circuit is subjected to anti-interference treatment using the interference control method described above.

[0017] After adopting the above solution, the external clock circuit of the radio frequency integrated circuit of the present invention is equipped with a second crystal oscillator path. When frequency doubling interference exists, its working crystal oscillator can be switched from the first crystal oscillator to the second crystal oscillator, which is equivalent to switching to another working system, and thus there is no interference problem caused by the first crystal oscillator. At the same time, because the working crystal oscillator is directly switched, there is no need to consider the voltage control range of the crystal oscillator. Compared with the prior art, the crystal oscillator can be selected from conventional models, which not only reduces the cost and facilitates the selection of components, but also, since a dual crystal oscillator path is used, it can handle frequency doubling interference of walkie-talkie reception in various frequency bands and different bandwidths, with a wide range of applications and high compatibility.

[0018] Furthermore, based on the same principle, the present invention can also address the problem of transmitting sideband harmonics. Attached Figure Description

[0019] Figure 1 This is a circuit block diagram of the external clock circuit of the radio frequency integrated circuit of the present invention; Figure 2 This is a schematic diagram of the external clock circuit of the radio frequency integrated circuit of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention. The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0021] The external clock circuit of the radio frequency integrated circuit of the present invention, such as Figure 1 As shown, it includes a power supply system, a microprocessor, a first crystal oscillator path, a second crystal oscillator path, a switching switch, and a third filter circuit; The power supply system provides operating power to the entire external clock circuit; The first crystal oscillator path includes a first crystal oscillator and a first filter circuit connected in sequence; wherein, the first filter circuit may be a low-pass filter circuit; in order to ensure the frequency stability and temperature stability of the crystal oscillator, the first crystal oscillator is preferably a temperature-compensated crystal oscillator; The second crystal oscillator path includes a power supply switch, a second crystal oscillator, and a second filter circuit connected in sequence; wherein, the second filter circuit may be a low-pass filter circuit; in order to ensure the frequency stability and temperature stability of the crystal oscillator, the second crystal oscillator is preferably a temperature-compensated crystal oscillator; The output terminal of the microprocessor is connected to the switching control terminal of the power supply switch and the switching control terminal of the switching switch, respectively. The output of the switching switch is connected to the input of the third filtering circuit, and the output of the third filtering circuit provides a clock signal to the radio frequency integrated circuit of the walkie-talkie; wherein, the third filtering circuit can be a low-pass filter circuit; The oscillation frequency of the first crystal oscillator and the oscillation frequency of the second crystal oscillator are non-integer multiples of each other. During operation, the first crystal oscillator is the main crystal oscillator and the second crystal oscillator is the backup crystal oscillator. The microprocessor contains a crystal oscillator interference lookup table, which records integer multiples of the oscillation frequency of the first crystal oscillator that fall within the operating frequency range of the walkie-talkie. When the operating frequency of the walkie-talkie is not in the crystal oscillator interference reference table, the microprocessor outputs a control signal to the switching switch, and the switching switch connects the first crystal oscillator path, so that the radio frequency integrated circuit of the walkie-talkie operates in a mode with the first crystal oscillator as the reference frequency source. When the operating frequency of the walkie-talkie falls within the crystal oscillator interference reference table, the microprocessor outputs a control signal to the switching switch and the power supply switch, thereby connecting the second crystal oscillator path through the switching switch and the power supply switch, so that the radio frequency integrated circuit operates in a mode with the second crystal oscillator as the reference frequency source.

[0022] In this invention, the frequency points where the sideband harmonics of the radio frequency integrated circuit do not meet the standard when operating in the first crystal oscillator path can also be added to the crystal oscillator interference comparison table, so that the problem of transmitting sideband harmonics can be dealt with at the same time.

[0023] As a specific example, such as Figure 2 As shown, the external clock circuit of the radio frequency integrated circuit of the present invention includes a power supply system, a microprocessor, a first crystal oscillator path, a second crystal oscillator path, a switching switch U1, and a third low-pass filter circuit (composed of an inductor L5 and a capacitor C10). The power supply system provides a 3.3V operating power to the entire external clock circuit; The first crystal oscillator path includes a first temperature-compensated crystal oscillator X1 and a first low-pass filter circuit (composed of inductor L2 and capacitors C3 and C4). The fourth pin of the first temperature-compensated crystal oscillator X1 is its power supply terminal, the first and second pins are grounded, and the third pin is its output terminal. The output terminal of the first temperature-compensated crystal oscillator X1 is connected to the input terminal of the first low-pass filter circuit. The second crystal oscillator path includes a power supply switch Q1 (model UMC4N), a second temperature-compensated crystal oscillator X2, and a second low-pass filter circuit (composed of inductor L4 and capacitors C7 and C8). Pin 3 of the power supply switch Q1 is its power supply terminal, pin 1 is grounded, pin 2 is the switching control terminal, pin 4 is the output terminal, and pin 5 is left floating. Pin 4 of the second temperature-compensated crystal oscillator X2 is its input terminal. The output terminal of the power supply switch Q1 is connected to the input terminal of the second temperature-compensated crystal oscillator X2. Pins 1 and 2 of the second temperature-compensated crystal oscillator X2 are grounded, and pin 3 is its output terminal. The output terminal of the second temperature-compensated crystal oscillator X2 is connected to the input terminal of the second low-pass filter circuit. The oscillation frequency of the first temperature-compensated crystal oscillator X1 and the oscillation frequency of the second temperature-compensated crystal oscillator X2 are non-integer multiples of each other. The oscillation frequency of the first temperature-compensated crystal oscillator X1 can be one of 19.2MHz, 20MHz, 24MHz, 25MHz, 26MHz, 38.4MHz, 40MHz, 48MHz, 50MHz, and 52MHz; the oscillation frequency of the second temperature-compensated crystal oscillator X2 can also be one of 19.2MHz, 20MHz, 24MHz, 25MHz, 26MHz, 38.4MHz, 40MHz, 48MHz, 50MHz, and 52MHz, as long as the oscillation frequencies of the two are non-integer multiples of each other.

[0024] Pin 1 of the switch U1 is its input terminal, which is connected to the output terminal of the first low-pass filter circuit; pin 3 of the switch U1 is its other input terminal, which is connected to the output terminal of the second low-pass filter circuit; pin 2 of the switch U1 is grounded, pin 5 is the power supply terminal, pin 6 is the switching control terminal, and pin 4 is the output terminal, which outputs the clock signal to the RF integrated circuit through the third low-pass filter circuit (composed of inductor L5 and capacitor C10).

[0025] The output of the second low-pass filter circuit is also output through capacitor C9, which can provide a reference clock signal for other integrated circuits.

[0026] The output terminal of the microprocessor is connected to the switching control terminal (pin 2) of power supply switch Q1 and the switching control terminal (pin 6) of switching switch U1, respectively.

[0027] In this invention, during operation, the first temperature-compensated crystal oscillator X1 is the main crystal oscillator, and the second temperature-compensated crystal oscillator X2 is the backup crystal oscillator. The microprocessor establishes a crystal oscillator interference lookup table, which records integer multiples of the oscillation frequency of the first temperature-compensated crystal oscillator X1 that fall within the operating frequency range of the walkie-talkie. Furthermore, the crystal oscillator interference lookup table can also include frequencies where the sideband harmonics of the RF integrated circuit are substandard when operating through the first crystal oscillator path, thus simultaneously addressing the issue of transmitted sideband harmonics.

[0028] The interference control method for the external clock circuit of the radio frequency integrated circuit of the present invention is as follows: First, a crystal oscillator interference lookup table is established in the microprocessor. Specifically, integer multiples of the oscillation frequency of the first temperature-compensated crystal oscillator X1, falling within the operating frequency range of the walkie-talkie, are entered into the microprocessor's memory. The transmit sideband harmonics of the walkie-talkie can also be tested using conventional testing tools and software to identify the frequency points where the walkie-talkie's RF integrated circuit fails to meet the sideband harmonic standards under the operation of the first temperature-compensated crystal oscillator X1 (each point is measured in 5kHz increments; frequency points with sideband harmonics exceeding the domestic and international standard of -36dBm are considered non-compliant). These non-compliant sideband harmonic frequencies are then entered into the microprocessor's memory. This establishes the crystal oscillator interference lookup table within the microprocessor.

[0029] Before starting work, the user sets the working frequency of the walkie-talkie as needed (either by setting via the keyboard or by programming via a host computer; the working frequency is a specific frequency within the walkie-talkie's operating frequency range).

[0030] During operation, the microprocessor compares the operating frequency with the crystal oscillator interference lookup table to determine whether the operating frequency is a harmonic interference frequency of the first temperature-compensated crystal oscillator X1 or a frequency where the transmitted sideband harmonics are substandard. Specifically: The reference clock generated by the first temperature-compensated crystal oscillator X1 is filtered by the first low-pass filter circuit to remove high-frequency components and enters the switching switch U1 from pin 3. If the operating frequency is not in the crystal oscillator interference lookup table, the microprocessor's I / O output terminal simultaneously outputs a low level to the switching switch U1 and the power supply switch Q1, controlling the switching switch U1 to conduct pins 3 and 4, and controlling the power supply switch Q1 to disconnect the power supply to the second temperature-compensated crystal oscillator X2 (so that when the first temperature-compensated crystal oscillator X1 is used, the second temperature-compensated crystal oscillator X2 does not work, reducing the power consumption of the walkie-talkie and increasing the battery life of the walkie-talkie). The reference clock generated by the first temperature-compensated crystal oscillator X1 is output from pin 4 of the switching switch U1 and is supplied to the radio frequency integrated circuit after being purified by the third low-pass filter circuit. Simultaneously, the microprocessor sends the corresponding setting value of the oscillation frequency of the first temperature-compensated crystal oscillator X1 to the radio frequency integrated circuit, and calculates the setting value of the operating frequency of the radio frequency integrated circuit using the calculation formula (current operating frequency * frequency division ratio * 2^24 / oscillation frequency of the first temperature-compensated crystal oscillator). The setting value of the operating frequency of the radio frequency integrated circuit is then sent to the radio frequency integrated circuit for setting, thereby enabling the radio frequency integrated circuit to operate in a mode with the first temperature-compensated crystal oscillator X1 as the reference frequency source.

[0031] The reference clock generated by the second temperature-compensated crystal oscillator X2 is filtered by the second low-pass filter circuit to remove high-frequency components and enters the switching switch U1 from pin 1. If the operating frequency is in the crystal oscillator interference lookup table, the microprocessor's I / O output simultaneously outputs a high level to the switching switch U1 and the power supply switch Q1, controlling pins 1 and 4 of the switching switch U1 to conduct and controlling the power supply switch Q1 to conduct. The 3V3 power supply in the power supply system supplies power to the second temperature-compensated crystal oscillator X2 through the power supply switch Q1. The reference clock generated by the second temperature-compensated crystal oscillator X2 is output from pin 4 of the switching switch U1, purified by the third low-pass filter circuit, and then supplied to the RF integrated circuit. At the same time, the microprocessor sends the corresponding setting value of the oscillation frequency of the second temperature-compensated crystal oscillator X2 to the RF integrated circuit, and calculates the setting value of the RF integrated circuit's operating frequency using the calculation formula (current operating frequency * division ratio * 2^24 / oscillation frequency of the second temperature-compensated crystal oscillator). This setting value of the RF integrated circuit's operating frequency is then sent to the RF integrated circuit for setting, thereby enabling the RF integrated circuit to operate in a mode with the second temperature-compensated crystal oscillator X2 as the reference frequency source.

[0032] After adopting the above solution, the external clock circuit of the radio frequency integrated circuit of the present invention is equipped with a second crystal oscillator path. When there is frequency doubling interference or transmit sideband harmonics, its working crystal oscillator can be switched from the first temperature-compensated crystal oscillator X1 to the second temperature-compensated crystal oscillator X2, which is equivalent to switching to another working system, and thus there is no interference problem caused by the first temperature-compensated crystal oscillator X1. At the same time, because the working crystal oscillator is directly switched, there is no need to consider the voltage control range of the crystal oscillator. Compared with the prior art, both the first temperature-compensated crystal oscillator X1 and the second temperature-compensated crystal oscillator X2 can be selected from conventional models (such as 19.2MHz, 20MHz, 24MHz, 25MHz, 26MHz, 38.4MHz, 40MHz, 48MHz, 50MHz or 52MHz, as long as their oscillation frequencies are not integer multiples of each other). This not only reduces costs and facilitates the selection of components, but also, because a dual crystal oscillator path is used, it can handle frequency doubling interference received by walkie-talkies in various frequency bands and with different bandwidths, resulting in a wide range of applications and high compatibility.

[0033] In this invention, since the first temperature-compensated crystal oscillator X1 is a conventional type of crystal oscillator, it can also provide a reference clock for other integrated circuits of the walkie-talkie.

[0034] The walkie-talkie of the present invention uses the external clock circuit of the radio frequency integrated circuit as described above.

[0035] Another walkie-talkie of the present invention employs the interference control method described above for anti-interference processing of its external clock circuit of the radio frequency integrated circuit.

[0036] The following is a specific application example to further illustrate the invention.

[0037] In this application example, the radio frequency integrated circuit uses a half-duplex TDD FM transceiver of model BK4819, the oscillation frequency of the first temperature-compensated crystal oscillator X1 is 38.4MHz, and the oscillation frequency of the second temperature-compensated crystal oscillator X2 is 26MHz.

[0038] Taking the operating frequency range of the walkie-talkie as an example (400~470MHz), the first temperature-compensated crystal oscillator X1 has frequency points of 38.4MHz*11=422.4MHz and 38.4MHz*12=460.8MHz within this operating frequency range, and the second temperature-compensated crystal oscillator X2 has frequency points of 26MHz*16=416MHz, 26MHz*17=442MHz and 26MHz*18=468MHz within this operating frequency range. Using conventional testing tools and software, each point was measured in 5kHz increments. Frequency points where the sideband harmonics exceeded the domestic and international standard of -36dBm were considered non-compliant. The tests showed that the non-compliant sideband harmonic frequencies of the first temperature-compensated crystal oscillator X1 within the operating frequency range were 421.9MHz~422.9MHz and 460.3MHz~461.3MHz, and the non-compliant sideband harmonic frequencies of the second temperature-compensated crystal oscillator X2 within the operating frequency range were 415.5MHz~416.5MHz, 441.5MHz~442.5MHz, and 467.5MHz~468.5MHz.

[0039] The RF integrated circuit has one register for setting the external clock circuit mode and two registers for setting the operating frequency of the RF integrated circuit. The setting value for the 38.4MHz external clock mode is 1011, and the setting value for the 26MHz external clock mode is 0000. Furthermore, the RF integrated circuit has a division ratio of 4 in the frequency range of 400~470MHz.

[0040] For example, if the user sets the operating frequency of the walkie-talkie to 400.125MHz, the microprocessor compares this frequency with a crystal oscillator interference table. It determines that 400.125MHz is neither the frequency of the first temperature-compensated crystal oscillator X1's harmonic multiplication, nor the frequency where the transmit sideband harmonics are substandard. Simultaneously, the microprocessor's I / O output outputs a low level to pin 6 of the switch U1 and pin 2 of the power switch Q1, controlling pins 3 and 4 of the switch U1 to conduct and power switch Q1 to be off, thus enabling the external clock circuit to operate on the first crystal oscillator path. The microprocessor then sends the corresponding setting value 1011 for the 38.4MHz oscillation frequency of the first temperature-compensated crystal oscillator to the register in the RF integrated circuit used to set the external clock circuit mode, causing the RF integrated circuit to operate in an external clock mode with the external crystal oscillator at 38.4MHz. Furthermore, the microprocessor calculates the following using the frequency calculation formula of the RF integrated circuit (current operating frequency * division ratio * 2^24 / oscillation frequency of the first temperature-compensated crystal oscillator): 400.125 * 4 * 2^24 / 38.4 = 699269120. This is converted to hexadecimal as 29AE0000 and divided into two bytes, 29AE and 0000. These two hexadecimal values, 29AE and 0000, are sent to the two registers in the RF integrated circuit used to set the operating frequency, thereby enabling the RF integrated circuit to operate at a frequency of 400.125MHz with an external clock mode of 38.4MHz external crystal oscillator. For example, if the user sets the walkie-talkie's operating frequency to 422.4MHz, the microprocessor compares this frequency with a crystal oscillator interference table and determines that 422.4MHz is the frequency of the first temperature-compensated crystal oscillator X1's frequency multiplication interference. Simultaneously, the microprocessor's I / O output outputs a high level to pin 6 of the switch U1 and pin 2 of the power supply switch Q1, controlling pins 1 and 4 of the switch U1 to conduct, and controlling the power supply switch Q1 to conduct. The 3V3 power supply in the power supply system then powers the second temperature-compensated crystal oscillator X2 through the power supply switch Q1, enabling the external clock circuit to operate on the second crystal oscillator path. The microprocessor sends the corresponding setting value 0000 for the second temperature-compensated crystal oscillator's 26MHz oscillation frequency to the register in the RF integrated circuit used to set the external clock circuit mode, causing the RF integrated circuit to operate in an external clock mode with the external crystal oscillator at 26MHz. Furthermore, the microprocessor calculates the frequency using the RF integrated circuit's frequency calculation formula (current operating frequency * division ratio * 2^24 / oscillation frequency of the second temperature-compensated crystal oscillator): 422.4 * 4 * 2^24 / 26 = 1090260929. This is converted to hexadecimal as 40FC0FC1 and divided into two bytes, 40FC and 0FC1. These two hexadecimal values, 40FC and 0FC1, are sent to two registers in the RF integrated circuit used to set the operating frequency. This allows the RF integrated circuit to operate at a frequency of 422.4MHz with an external clock mode of 26MHz for the external crystal oscillator, thus avoiding the 11th-fold frequency interference point of the first temperature-compensated crystal oscillator at 38.4MHz, which is also 422.4MHz.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An interference control method for an external clock circuit of a radio frequency integrated circuit, characterized in that: In the external clock circuit of the radio frequency integrated circuit of the walkie-talkie, a first crystal oscillator path with a first crystal oscillator and a second crystal oscillator path with a second crystal oscillator are provided, wherein the oscillation frequency of the first crystal oscillator and the oscillation frequency of the second crystal oscillator are non-integer multiples of each other. A crystal oscillator interference comparison table is established, which records integer multiples of the oscillation frequency of the first crystal oscillator that fall within the operating frequency range of the walkie-talkie. When the operating frequency of the walkie-talkie is not in the crystal oscillator interference reference table, the first crystal oscillator path is activated, so that the radio frequency integrated circuit operates in a mode with the first crystal oscillator as the reference frequency source. When the operating frequency of the walkie-talkie is in the crystal oscillator interference reference table, the second crystal oscillator path is activated, causing the radio frequency integrated circuit to operate in a mode with the second crystal oscillator as the reference frequency source.

2. The interference control method for the external clock circuit of the radio frequency integrated circuit according to claim 1, characterized in that: The crystal oscillator interference comparison table also records the frequency points where the sideband harmonics of the radio frequency integrated circuit do not meet the standard when operating in the first crystal oscillator path.

3. The interference control method for the external clock circuit of the radio frequency integrated circuit according to claim 1, characterized in that: Both the first crystal oscillator and the second crystal oscillator are temperature-compensated crystal oscillators.

4. The interference control method for the external clock circuit of the radio frequency integrated circuit according to claim 1, characterized in that: The oscillation frequency of the first crystal oscillator is 19.2MHz, 20MHz, 24MHz, 25MHz, 26MHz, 38.4MHz, 40MHz, 48MHz, 50MHz or 52MHz; the oscillation frequency of the second crystal oscillator is 19.2MHz, 20MHz, 24MHz, 25MHz, 26MHz, 38.4MHz, 40MHz, 48MHz, 50MHz or 52MHz.

5. An external clock circuit for a radio frequency integrated circuit, characterized in that: Includes a power supply system, a microprocessor, a first crystal oscillator path, a second crystal oscillator path, a switching switch, and a third filter circuit; The power supply system provides operating power to the entire external clock circuit; The first crystal oscillator path includes a first crystal oscillator and a first filter circuit connected in sequence; The second crystal oscillator path includes a power supply switch, a second crystal oscillator, and a second filter circuit connected in sequence; The output terminal of the microprocessor is connected to the switching control terminal of the power supply switch and the switching control terminal of the switching switch, respectively. The output terminal of the switching switch is connected to the input terminal of the third filter circuit, and the output terminal of the third filter circuit provides a clock signal to the radio frequency integrated circuit of the walkie-talkie. The oscillation frequency of the first crystal oscillator and the oscillation frequency of the second crystal oscillator are non-integer multiples of each other; The microprocessor contains a crystal oscillator interference lookup table, which records integer multiples of the oscillation frequency of the first crystal oscillator that fall within the operating frequency range of the walkie-talkie. The microprocessor is used to connect the first crystal oscillator path via the switching switch when the operating frequency of the walkie-talkie is not in the crystal oscillator interference reference table, so that the radio frequency integrated circuit of the walkie-talkie operates in a mode with the first crystal oscillator as the reference frequency source. Furthermore, when the operating frequency of the walkie-talkie falls within the crystal oscillator interference reference table, the second crystal oscillator path is connected via the switching switch and the power supply switch, causing the radio frequency integrated circuit to operate in a mode with the second crystal oscillator as the reference frequency source.

6. The external clock circuit for the radio frequency integrated circuit according to claim 5, characterized in that: The crystal oscillator interference comparison table also records the frequency points where the sideband harmonics of the radio frequency integrated circuit do not meet the standard when operating in the first crystal oscillator path.

7. The external clock circuit for the radio frequency integrated circuit according to claim 5, characterized in that: Both the first crystal oscillator and the second crystal oscillator are temperature-compensated crystal oscillators.

8. The external clock circuit for the radio frequency integrated circuit according to claim 5, characterized in that: The oscillation frequency of the first crystal oscillator is 19.2MHz, 20MHz, 24MHz, 25MHz, 26MHz, 38.4MHz, 40MHz, 48MHz, 50MHz or 52MHz; the oscillation frequency of the second crystal oscillator is 19.2MHz, 20MHz, 24MHz, 25MHz, 26MHz, 38.4MHz, 40MHz, 48MHz, 50MHz or 52MHz.

9. A walkie-talkie, characterized in that: The external clock circuit of its radio frequency integrated circuit is subjected to anti-interference processing using the interference control method described in any one of claims 1-4.

10. A walkie-talkie, characterized in that: The external clock circuit of its radio frequency integrated circuit adopts the external clock circuit of the radio frequency integrated circuit as described in any one of claims 5-8.

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