TWI505661B - Amplitude modulation interference avoidance method, device, and amplitude modulation receiver - Google Patents

Description

Amplitude modulation interference avoiding method, device and amplitude modulation receiver thereof

The present invention relates to an amplitude modulation receiver, and more particularly to an amplitude modulation interference avoidance method, apparatus and amplitude modulation receiver therefor.

The amplitude modulation technique can be applied to a broadcast signal transmitting and receiving system of a broadcasting station, and in an amplitude modulation receiver, a pulse width modulator may be used to pulse the demodulated, sampled, and quantized digital signals. Pulse width modulation (PWM) to obtain a pulse width modulation signal. The pulse width modulation signal is then transmitted to the speaker to cause the speaker to play the sound corresponding to the broadcast station.

In amplitude modulation receivers, the pulse width modulator described above is conventionally a Class AB amplifier. With advances in semiconductor fabrication and wafer integration technology, Class AB amplifiers are gradually being replaced by Class D amplifiers. However, regardless of the type of amplifier used in the amplitude modulation receiver, since the pulse width modulation of the demodulated, sampled, and quantized digital signals is required, it is necessary to give the pulse width modulation a pulse width modulation. Frame (PWM frame) frequency. Unfortunately, if the pulse width modulation signal itself or its harmonic wave is close to the radio frequency, intermediate frequency, or image frequency used by the amplitude modulation receiver. , the pulse width modulation signal itself or its harmonics may The correctness of the demodulated, sampled, and quantized digital signals is degraded because of the influence of the RF signal received by the amplitude modulation receiver, the mixed intermediate frequency signal or the image frequency signal. In other words, if the pulse width modulation frame frequency is not taken care of, the pulse width modulation signal itself or its harmonics may be an interference signal that becomes a radio frequency signal, an intermediate frequency signal, or a picture frequency signal.

Please refer to FIG. 1. FIG. 1 is a block diagram of a conventional amplitude modulation receiver. The amplitude modulation receiver 1 includes an antenna 100, a radio frequency amplifier 101, a tuning circuit 102, a local end oscillator 103, a mixer 104, an intermediate frequency amplifier 105, an amplitude demodulator 106, an analog digital converter 107, and a pulse width modulation. The transformer 108 is connected to the speaker 109. The antenna 100 is coupled to the RF amplifier 101, and the tuning circuit 102 is coupled to the RF amplifier 101 and the local oscillator 103. The mixer 104 is coupled to the local oscillator 103 and the intermediate frequency amplifier 105, and the intermediate frequency amplifier 105 is coupled to the amplitude demodulator 106. The amplitude demodulator 106 is coupled to the analog digital converter 107. The analog digital converter 107 is coupled to the pulse width modulator 108, and the pulse width modulator 108 is coupled to the speaker 109.

The antenna 100 is configured to receive a radio frequency signal from an amplitude modulated by a broadcast station, and the radio frequency amplifier 101 is configured to perform low noise amplification on the radio frequency signal. The tuning circuit 102 is configured to control the local end oscillation frequency of the local end oscillation signal generated by the radio frequency amplifier 101 noise filtering band and the local end oscillator 103 according to the tuning signal received by the tuning circuit 102. The mixer 104 is configured to mix the RF signal output by the RF amplifier 101 with the local oscillation signal output by the local oscillator 103 to generate an intermediate frequency signal and a image frequency signal, wherein the image frequency signal is generally The frequency amplifier 105 is filtered out.

The intermediate frequency amplifier 105 is configured to perform low noise amplification on the intermediate frequency signal, thereby filtering out unnecessary image frequency signals. The amplitude demodulator 106 is configured to perform amplitude demodulation on the intermediate frequency signal output by the intermediate frequency amplifier 105 to generate an amplitude demodulated signal. The analog to digital converter 107 is used to perform analog bit conversion (sampling and quantization) on the amplitude demodulated signal to generate a digital signal. The pulse width modulator 108 performs pulse width modulation according to the digital signal output by the analog digital converter to generate a pulse width modulation signal. The speaker 109 generates a sound in accordance with the pulse width modulation signal.

Please note that in general, the frequency of the amplitude-modulated RF signal is about 540 thousand to 1710 kHz, the frequency of the intermediate frequency signal is 455 thousand or 262.5 kHz, and the local end oscillation of the local-end oscillating signal The frequency is 995 thousand to 2165 kHz. For example, if the pulse width modulation block 108 uses a pulse width modulation frame frequency that is 8 times the sampling frequency of the analog digital converter 107, and the sampling frequency is 48 kHz, the pulse width modulation frame frequency At 384 kHz, the second harmonic of the pulse width modulated signal (with a frequency of 768 kHz) will interfere with the RF signal at 760 kHz.

In summary, in order to ensure the correctness of the digital signal demodulated, sampled and quantized by the amplitude modulation receiver to ensure the quality of the sound played by the speaker, a pulse width modulation signal or its harmonic is needed. The mechanism by which a wave interferes with a radio frequency signal, an intermediate frequency signal, or a picture frequency signal.

Embodiments of the present invention provide an amplitude modulation interference avoidance method, and the amplitude modulation interference avoidance method is used in an amplitude modulation receiver. First, the mode of operation is determined, where the mode of operation determines the range of frequencies. Then, the local end oscillation signal is frequency-divided according to the frequency division to generate a pulse width modulation frame frequency, wherein the local end oscillation signal is used to mix with the radio frequency signal received by the amplitude modulation receiver. Then, according to the local end oscillation frequency or the pulse width modulation frame frequency of the local end oscillation signal, whether to adjust the frequency division and whether to output the signal having the pulse width modulation frame frequency information is determined.

In addition, an embodiment of the present invention further provides an amplitude modulation interference avoiding apparatus having a plurality of circuits for performing the steps of the amplitude modulation interference avoiding method. In addition, an embodiment of the present invention further provides an amplitude modulation receiver having the amplitude modulation interference avoiding device.

In summary, the amplitude modulation interference avoiding method provided by the embodiment of the present invention, The device and its amplitude modulation receiver are used to provide a signal to avoid the pulse width modulation signal or its harmonic interference radio frequency signal, intermediate frequency signal or image frequency signal. The above-described amplitude modulation interference avoidance method and apparatus can select an operating mode to define a range of frequency divisions according to a user's selection or system requirements to obtain a trade off between power efficiency or reduced interference effects.

1, 2‧‧‧Amplitude modulation receiver

100, 200‧‧‧ antenna

101, 201‧‧‧RF amplifier

102, 202‧‧‧ tuned circuit

103, 203‧‧‧ local end oscillator

104, 204‧‧‧ Mixer

105, 205‧‧‧Intermediate frequency amplifier

106, 206‧‧‧Amplitude demodulator

107, 207‧‧‧ analog digital converter

108, 208‧‧‧ pulse width modulator

109, 209‧‧‧ Speakers

210, 3, 5‧‧‧Amplitude modulation interference avoidance device

300, 501‧‧‧ first decision circuit

301‧‧‧Local end oscillation frequency detector

304, 503‧‧‧First threshold frequency comparison circuit

302, 504‧‧‧ second decision circuit

303, 502‧‧ ‧ frequency divider

505‧‧‧second threshold frequency comparison circuit

305, 506‧‧‧ third decision circuit

S400~S606‧‧‧Step procedure

1 is a block diagram of a conventional amplitude modulation receiver.

2 is a block diagram of an amplitude modulation receiver in accordance with an embodiment of the present invention.

3 is a block diagram of an amplitude modulation interference avoidance apparatus according to an embodiment of the present invention.

4 is a flow chart of an amplitude modulation interference avoidance method according to an embodiment of the present invention.

FIG. 5 is a block diagram of an amplitude modulation interference avoiding apparatus according to another embodiment of the present invention.

6 is a flow chart of a method for avoiding amplitude modulation interference according to another embodiment of the present invention.

Various illustrative embodiments are described more fully hereinafter with reference to the accompanying drawings. However, the inventive concept may be embodied in many different forms and should not be construed as being limited to the illustrative embodiments set forth herein. Rather, these exemplary embodiments are provided so that this invention will be in the In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Similar numbers always indicate similar components.

It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, such elements are not limited by the terms. These terms are used to distinguish one element from another. Thus, a first element discussed below could be termed a second element without departing from the teachings of the novel. As used herein, the term "and/or" includes any of the associated listed items and all combinations of one or more.

Embodiments of the present invention provide a method and device for avoiding amplitude modulation interference avoidance The amplitude modulation receiver, the amplitude modulation interference avoiding method, and the amplitude modulation receiver thereof can avoid the pulse width modulation signal or its harmonic interference radio frequency signal, intermediate frequency signal or image frequency signal. In the embodiment, the amplitude modulation interference avoiding method and apparatus perform a frequency division operation on the local end oscillation signal according to the frequency division to generate a pulse width modulation frame frequency.

The above amplitude modulation interference avoiding method and apparatus may check whether the obtained pulse width modulation frame frequency is greater than a first threshold frequency corresponding to its operation mode. If the pulse width modulation frame frequency is greater than the corresponding first threshold frequency, it indicates that the current pulse width modulation signal or its harmonics may cause interference to the radio frequency signal, the intermediate frequency signal or the image frequency signal, and therefore, the frequency is divided. It will be incremented to reduce the pulse width modulation frame frequency to avoid interference of the pulse width modulation signal or its harmonics on the RF signal, IF signal or image frequency signal. In addition, if the local oscillation frequency is lower than the previous local oscillation frequency, or the pulse width modulation frame frequency is less than the second threshold frequency corresponding to the operation mode, the frequency division will be reset or decremented to adjust the pulse width. The variable frame frequency is appropriately increased to increase power efficiency.

The above-mentioned frequency division has different ranges according to the operation mode. When the operation mode is the first mode, the frequency division may be an integer of 3-6, and when the operation mode is the second mode, the frequency division may be 5-9. Integer. The mode of operation can be selected by the user or determined according to system requirements.

In the embodiment of the present invention, the pulse width modulation frame frequency generated by the first mode is mostly greater than the pulse width modulation frame frequency generated by the second mode, so the power efficiency of the second mode is better, but if the first The pulse width modulation signal of the mode or its low-order harmonics may directly become interference, and the effect on the amplitude modulation receiver will be more serious. Therefore, in the first mode, the pulse width modulation frame frequency is greater than the first threshold frequency, so the number of adjustments of the frequency division is greater than the number of adjustments of the frequency division of the second mode.

Compared with the first mode, since the pulse width modulation frame frequency of the second mode is lower, the higher-order harmonic comparison of the pulse width modulation signal of the second mode may be directly It becomes interference and this interference has a lesser effect on the amplitude modulation receiver. In other words, the second mode can further reduce the effects of interference compared to the first mode.

It can be seen from the above that the amplitude modulation interference avoiding method and apparatus can select the operating mode to define the range of the frequency division according to the user's selection or system requirements, so as to obtain a tradeoff between power efficiency or reducing the interference effect. In addition, it should be understood that whether the frequency of the check pulse width modulation frame is greater than the first threshold frequency corresponding to the operation mode thereof may further check whether the local end oscillation frequency is greater than the third threshold frequency (which is the first threshold) The frequency is replaced by the product of the current division frequency. Similarly, if the frequency of the pulse width modulation box is less than the second threshold frequency corresponding to the operation mode, the same may be used to check whether the local oscillation frequency is less than the fourth threshold frequency (which is the second threshold frequency and the current frequency division). Replace the product by).

Please refer to FIG. 2. FIG. 2 is a block diagram of an amplitude modulation receiver according to an embodiment of the present invention. The amplitude modulation receiver 2 includes an antenna 200, a radio frequency amplifier 201, a tuning circuit 202, a local end oscillator 203, a mixer 204, an intermediate frequency amplifier 205, an amplitude demodulator 206, an analog digital converter 207, and a pulse width modulation. The transformer 208, the speaker 209 and the amplitude modulation interference avoiding device 210. The antenna 200 is coupled to the RF amplifier 201, and the tuning circuit 202 is coupled to the RF amplifier 201 and the local oscillator 203. The mixer 204 is coupled to the local oscillator 203 and the intermediate frequency amplifier 205, and the intermediate frequency amplifier 205 is coupled to the amplitude demodulator 206. The amplitude demodulator 206 is coupled to the analog digital converter 207. The analog digital converter 207 is coupled to the pulse width modulator 208, and the pulse width modulator 208 is coupled to the speaker 209. In addition, the amplitude modulation interference avoiding device 210 is coupled to the mixer 203 and the pulse width modulator 208.

The antenna 200 is configured to receive a radio frequency signal from an amplitude modulated by a broadcast station, and the radio frequency amplifier 201 is configured to perform low noise amplification on the radio frequency signal. The tuning circuit 202 is configured to control the local end oscillation frequency of the local end oscillation signal generated by the noise filtering band of the radio frequency amplifier 201 and the local end oscillator 203 according to the tuning signal received by the tuning circuit 202. The mixer 204 is configured to mix the RF signal output by the RF amplifier 201 with the local oscillation signal output by the local oscillator 203 to generate The intermediate frequency signal and the image frequency signal, wherein the image frequency signal is generally filtered by the intermediate frequency amplifier 205.

The intermediate frequency amplifier 205 is configured to perform low noise amplification on the intermediate frequency signal, thereby filtering out unnecessary image frequency signals. The amplitude demodulator 206 is configured to perform amplitude demodulation on the intermediate frequency signal output by the intermediate frequency amplifier 205 to generate an amplitude demodulated signal. The analog to digital converter 207 is used to perform analog bit conversion (sampling and quantization) on the amplitude demodulated signal to generate a digital signal. The pulse width modulator 208 performs pulse width modulation according to the digital signal output from the analog-to-digital converter to generate a pulse width modulation signal, and the speaker 209 generates sound according to the pulse width modulation signal.

In the embodiment of the present invention, in order to prevent the pulse width modulation signal of the pulse width modulator 208 or its harmonics from becoming interference of the radio frequency signal, the intermediate frequency signal or the image frequency signal, the amplitude modulation interference avoiding device 210 The local end oscillation signal is received, and a signal having pulse width modulation frame frequency information is generated according to the local end oscillation frequency to the pulse width modulator 208.

The amplitude modulation interference avoidance device 210 has two operation modes, which are the first mode and the second mode, respectively. The operation mode is used to define the range of the frequency division. When the operation mode is the first mode, the frequency division may be an integer of 3-6, and when the operation mode is the second mode, the frequency division may be an integer of 5-9. The mode of operation can be selected by the user or determined according to system requirements.

The amplitude modulation interference avoidance device 210 checks whether the obtained pulse width modulation frame frequency is greater than a first threshold frequency corresponding to its mode of operation. If the pulse width modulation frame frequency is greater than the corresponding first threshold frequency, the amplitude modulation interference avoidance device 210 increments the frequency division (eg, from 3 to 4) to reduce the pulse width modulation frame frequency. In addition, the amplitude modulation interference avoiding device 210 also checks whether the current local end oscillation frequency is smaller than the previous local end oscillation frequency, or checks that the pulse width modulation frame frequency is smaller than the second threshold frequency corresponding to the operation mode thereof, and the amplitude modulation interference avoidance is avoided. The device 210 decrements the frequency (e.g., from 4 to 3) or resets the frequency (e.g., resets to 3).

In addition, the first and second threshold frequencies of the first mode may be the same as the second The first and second threshold frequencies of the mode, however, the invention is not limited thereto. In addition, the initial values of the frequency in the first and second modes are 3 and 5, respectively, but the invention is not limited thereto. Taking the local oscillation frequency range of 995 thousand to 2165 kHz as an example, if the frequency of the pulse width modulation signal in the class D amplifier in the speaker 209 is between about 200 kilograms and about 300 kilohertz, the first threshold The frequency can be 300 kHz and the second threshold frequency can be 200 kHz. Under different environmental requirements, the first and second threshold frequencies may be adjusted according to actual needs. Generally, the first threshold frequency and the second threshold frequency are related to the pulse width modulation of the class D amplifier in the speaker 209. The range of frequencies that change the signal.

Please refer to FIG. 3. FIG. 3 is a block diagram of an amplitude modulation interference avoiding apparatus according to an embodiment of the present invention. The amplitude modulation interference avoidance device 3 includes a first decision circuit 300, a local end oscillation frequency detector 301, a second decision circuit 302, a frequency divider 303, a first threshold frequency comparison circuit 304, and a third decision circuit 305. The first decision circuit 300 is coupled to the second decision circuit 302, and the local end oscillation frequency detector 301 is coupled to the second decision circuit 302. The second decision circuit 302 is coupled to the frequency divider 303. The frequency divider 303 is coupled to the first threshold frequency comparator 304 and the third decision circuit 305, and the first threshold frequency comparator 304 is coupled to the third decision circuit 305.

In this embodiment, the first decision circuit 300 receives the mode selection signal to determine that the amplitude modulation interference avoidance device 3 operates in the first mode or the second mode, thereby defining the range of the frequency division to be 3-6 or 5~ 9. The oscillating frequency detector 301 compares the current local end oscillation frequency with the previous local end oscillation frequency, and generates a detection result, and the detection result has information that the local local end oscillation frequency is smaller than the previous local end oscillation frequency. The second decision circuit 302 determines whether to reset the frequency division according to the detection result to output the frequency division to the frequency divider 303.

The frequency divider 303 divides the local end oscillation signal according to the frequency division to generate an oscillation signal having a pulse width modulation frame frequency. Next, the first threshold frequency comparison circuit 304 compares the pulse width modulation frame frequency with the first threshold frequency, and generates a first threshold frequency comparison result, wherein the first threshold frequency comparison result has a pulse width adjustment Whether the variable frame frequency is greater than the information of the first threshold frequency. The third decision circuit 305 determines whether to increment the frequency division according to the first threshold frequency comparison result, and determines whether to output a signal having the pulse width modulation frame frequency information.

Please refer to FIG. 3 and FIG. 4 simultaneously. FIG. 4 is a flowchart of the amplitude modulation interference avoiding method according to the embodiment of the present invention. The amplitude modulation interference avoiding method of FIG. 4 can be performed by the amplitude modulation interference avoiding device 3 of FIG. 3, but the invention is not limited thereto. First, in step S400, the first decision circuit 300 determines that the operation mode is the first or second mode according to the mode selection signal. If the operation mode is the first mode, step S401a is then executed, and if the operation mode is the second mode, step S401b is then executed.

In step S401a or step S401b, the second decision circuit 302 determines whether the current local end oscillation frequency is smaller than the previous local end oscillation frequency according to the detection result output by the local end oscillation frequency detection 301. If the local local oscillation frequency is lower than the previous local end oscillation frequency, step S402a or S402b is performed. If the local local oscillation frequency is not less than the previous local end oscillation frequency, step S403a or step S403b is executed. In step S402a or step S402b, the second decision circuit 302 resets the frequency division of the first or second mode, for example, to 3 or 5. In step S403a or step S403b, the frequency divider 303 performs frequency division on the current local end oscillation signal according to the current frequency division.

In step S404a or step S404b, the third decision circuit 305 determines whether the pulse width modulation frame frequency is greater than the first threshold frequency of the first or second mode according to the first threshold frequency comparison result of the first threshold frequency comparison circuit. If the pulse width modulation frame frequency is greater than the first threshold frequency, step S405a or step S405b is performed. If the pulse width modulation frame frequency is not greater than the first threshold frequency, step S406 is performed. In step S405a or step S405b, the third decision circuit 305 increments the frequency division, for example, increments 3 to 4, or increments 5 to 6. In step S406, the third decision circuit 305 outputs a signal having pulse width modulation frame frequency information.

Please refer to FIG. 5. FIG. 5 is a block diagram of an amplitude modulation interference avoiding apparatus according to another embodiment of the present invention. The amplitude modulation interference avoiding device 5 includes a first decision circuit 501. A frequency divider 502, a first threshold frequency comparison circuit 503, a second decision circuit 504, a second threshold frequency comparison circuit 505, and a third decision circuit 506. The first decision circuit 501 is coupled to the frequency divider 502, and the frequency divider 502 is coupled to the first threshold frequency comparison circuit 503, the second decision circuit 504, the second threshold frequency comparison circuit 505, and the third decision circuit 506. The second decision circuit 504 is coupled to the first threshold frequency comparison circuit 503 and the third decision circuit 506, and the second threshold frequency comparison circuit 505 is coupled to the third decision circuit 506.

In this embodiment, the first decision circuit 501 receives the mode selection signal to determine whether the amplitude modulation interference avoidance device 5 operates in the first mode or the second mode, thereby defining the range of the frequency division to be 3-6 or 5~ 9. The frequency divider 501 divides the local end oscillation signal according to the frequency division to generate an oscillation signal having a pulse width modulation frame frequency. The first threshold frequency comparison circuit 503 compares the pulse width modulation frame frequency with the first threshold frequency, and generates a first threshold frequency comparison result, wherein the first threshold frequency comparison result has a pulse width modulation frame frequency greater than the first Threshold frequency information.

The second decision circuit 504 determines whether to increment the frequency division according to the first threshold frequency comparison result, and notifies the third decision circuit 506 of the decision result. The second threshold frequency comparison circuit 505 compares the pulse width modulation frame frequency with the second threshold frequency to generate a second threshold frequency comparison result, wherein the second threshold frequency comparison result has a pulse width modulation frame frequency smaller than the second Threshold frequency information. The third decision circuit 506 determines whether to decrement the frequency according to the second threshold frequency comparison result, and determines whether to output the signal having the pulse width modulation frame frequency information according to the second threshold frequency comparison result and the decision result of the second decision circuit 504.

Please refer to FIG. 5 and FIG. 6 simultaneously. FIG. 6 is a flowchart of an amplitude modulation interference avoiding method according to another embodiment of the present invention. The amplitude modulation interference avoiding method of FIG. 6 can be performed by the amplitude modulation interference avoiding device 5 of FIG. 3, but the invention is not limited thereto. First, in step S600, the first decision circuit 501 determines that the operation mode is the first or second mode according to the mode selection signal. If the operation mode is the first mode, step S601a is performed next, and if the operation mode is the second mode, step S601b is followed. Being executed.

In step S601a or step S601b, the frequency divider 501 divides the local end oscillation signal according to the frequency division to generate an oscillation signal having a pulse width modulation frame frequency. Next, in step S602a or S602b, the second decision circuit 504 determines whether the pulse width modulation frame frequency is greater than the first threshold frequency of the first or second mode according to the first threshold frequency comparison result of the first threshold frequency comparison circuit 503. . If the pulse width modulation frame frequency is greater than the first threshold frequency, step S603a or step S603b is performed. If the pulse width modulation frame frequency is not greater than the first threshold frequency, step S604a or step S604b is performed. In step S603a or step S603b, the second decision circuit 504 increments the division frequency, for example, increments 3 to 4, or increments 5 to 6.

In step S604a or step S604b, the third decision circuit 506 determines whether the pulse width modulation frame frequency is smaller than the second threshold frequency of the first or second mode according to the second threshold frequency comparison result of the second threshold frequency comparison circuit 505. If the pulse width modulation frame frequency is less than the second threshold frequency, step S605a or step S605b is performed. If the pulse width modulation frame frequency is not less than the second threshold frequency, step S606 is performed. In step S605a and step S605b, the third decision circuit 506 decrements the division number, for example, decrements 5 to 4, or decrements 8 to 7. In step S606, the third decision circuit 506 is configured to output a signal having pulse width modulation frame frequency information.

It should be noted here that the detailed methods of the amplitude modulation interference avoidance apparatus of the above embodiment are not used in the present invention. Briefly, the amplitude modulation interference avoidance device has a plurality of circuits that can be used to perform the amplitude modulation interference avoidance method described above.

In summary, the amplitude modulation interference avoiding method and apparatus provided by the embodiments of the present invention and the amplitude modulation receiver thereof are used to provide a pulse width modulation signal or a harmonic interference radio frequency signal, an intermediate frequency signal, or Image frequency signal. In addition to the simple implementation manner, the amplitude modulation interference avoiding method and apparatus can select an operating mode to define a range of frequency division according to a user's selection or system requirements, in order to A trade-off is made between efficiency or reducing the effects of interference.

S400~S406‧‧‧Step procedure

Claims (9)

An amplitude modulation interference avoidance method for an amplitude modulation receiver includes: determining an operation mode, wherein the operation mode is a first mode or a second mode, and one of the first modes is divided by a frequency The range is different from the range of the frequency division of the second mode; the local end oscillation signal is divided according to the frequency division to generate a pulse width modulation frame frequency, wherein the local end oscillation signal is used to A radio frequency signal received by the amplitude modulation receiver is mixed; and determining whether to adjust the frequency division and determining whether the output has a pulse according to a local end oscillation frequency of the local end oscillation signal or the pulse width modulation frame frequency Wave width modulation of a frame frequency information. The amplitude modulation interference avoidance method of claim 1, wherein when the operation mode is the first mode, the frequency division is an integer of 3-6, and the initial value is 3; when the operation mode is In the second mode, the frequency division is an integer from 5 to 9, and the initial value is 5. The amplitude modulation interference avoidance method of claim 1, wherein the operation mode is selected by a user or determined by a system requirement. The amplitude modulation interference avoidance method of claim 1, wherein the frequency division is incremented when the pulse width modulation frame frequency is greater than a first threshold frequency. The amplitude modulation interference avoidance method of claim 4, wherein when the current local end oscillation frequency is smaller than the previous local end oscillation frequency, or the pulse width modulation frame frequency is less than a second threshold frequency, Decrement the division number or reset the division number. The amplitude modulation interference avoidance method of claim 5, wherein " when the pulse width modulation frame frequency is not greater than the first threshold frequency and the current local end oscillation frequency is not less than the previous local end oscillation frequency when "or" when the pulse width modulation frame frequency is not greater than the first threshold frequency and the pulse width modulation frame frequency is not the second threshold frequency is less than "outputs the pulse width modulation block frequency information The signal. An amplitude modulation interference avoiding device has a plurality of circuits for determining an operation mode, wherein the operation mode is a first mode or a second mode, and a range of the frequency of the first mode is different from the a range of frequency divisions of the second mode; dividing a local end oscillation signal according to the frequency division to generate a pulse width modulation frame frequency, wherein the local end oscillation signal is used with the amplitude modulation receiver Receiving a radio frequency signal for mixing; and determining whether to adjust the frequency division number and determining whether the output has a pulse width modulation frame according to a local end oscillation frequency of the local end oscillation signal or the pulse width modulation frame frequency A signal of frequency information. The amplitude modulation interference avoidance device of claim 7, wherein when the operation mode is the first mode, the frequency division is an integer of 3-6, and the initial value is 3; when the operation mode is In the second mode, the frequency division is an integer from 5 to 9, and its initial value is 5; and the operation mode is selected by a user or determined by a system requirement. The amplitude modulation interference avoidance device of claim 7, wherein when the pulse width modulation frame frequency is greater than a first threshold frequency, the frequency division frequency is incremented; when the current local end oscillation frequency is smaller than the previous one When the local end oscillation frequency, or the pulse width modulation frame frequency is less than a second threshold frequency, decrement the frequency division or reset the division frequency; when " the pulse width modulation frame frequency is not greater than the first threshold frequency And the current local end oscillation frequency is not less than the previous local end oscillation frequency " or " the pulse width modulation frame frequency is not greater than the first threshold frequency and the pulse width modulation frame frequency is not less than the second threshold frequency " When, the signal having the pulse width modulation frame frequency information is output.