Hybrid modulation method for suppressing EMI applied to motor driving chip

Abstract

This invention discloses a hybrid modulation method for suppressing EMI in motor drive chips. Step S1: The oscillation circuit connected to the charge pump circuit combines periodic modulation and random modulation to perform hybrid modulation. Periodic modulation is used for coarse adjustment, modulating the charging and discharging current of the oscillation circuit with a triangular wave signal to obtain a periodically changing oscillation frequency. Random modulation is used for fine adjustment, adjusting the output signal of the oscillation circuit. Based on the coarse adjustment, the oscillation circuit's edge jitters at a certain frequency, randomly changing the delay to slow down the switching edge speed. This invention discloses a hybrid modulation method for suppressing EMI in motor drive chips, employing a combination of periodic and random modulation techniques. Periodic modulation is used for coarse adjustment, and random modulation for fine adjustment, thereby reducing the EMI of the charge pump circuit.

Description

Technical Field

[0001] This invention belongs to the field of oscillation technology of charge pumps in motor drives, and specifically relates to a hybrid modulation method for suppressing EMI applied to motor drive chips. Background Technology

[0002] With the widespread adoption of portable and consumer electronic devices, electromagnetic interference (EMI) has become a critical issue in consumer electronics using serial communication systems, Class D switching power amplifiers, or switching power converters. This has led to concerns about EMI extending beyond its impact on electronic devices to include its potential effects on human health. In DC brushless motor drive circuits employing dual N-type power transistors, a high-voltage charge pump circuit is essential. When using a charge pump circuit with an integrated load capacitor, the switching frequency is increased to enhance its driving capability. Because the charge pump circuit operates under high-frequency, high-voltage conditions, high-slope voltage (dV / dt) or current nodes (dI / dt) occur during switching, exacerbating EMI problems.

[0003] The most effective way to reduce electromagnetic interference (EMI) is through spread spectrum clock generation circuits (SSCG), and there are various modulation methods. The first method is to introduce modulation into a PLL, including ΔΣ modulation and phase compensation. However, ΔΣ modulation may have quantization errors, increasing output jitter, while phase compensation's EMI reduction performance is lower than ΔΣ modulation. This method typically has a more complex circuit structure and is often used in higher frequency designs. The second method is direct modulation of a voltage-controlled oscillator (VCO). Modulation methods include periodic signal modulation, random signal modulation, and chaotic signal modulation. Chaotic signal modulation is more effective, but the inductors and capacitors used are not suitable for motor driver chips. Periodic modulation waveforms include triangular waves, sine waves, and Hershey Kiss waves. Although the spectrum modulated by Hershey Kiss waveforms becomes a near-uniform energy distribution, resulting in the best spread spectrum effect, it requires many registers, making it relatively complex and large in area. Triangular waves offer high controllability and are easier to implement, while also providing better spread spectrum effects than sine waves. Random modulation is more efficient than periodic modulation and has the least impact on audio performance, but true random signals are difficult to achieve, so pseudo-random signals are often used.

[0004] Therefore, further improvements will be made to address the aforementioned issues. Summary of the Invention

[0005] The main objective of this invention is to provide a hybrid modulation method for suppressing EMI in motor drive chips. This method combines periodic modulation and random modulation, using periodic modulation for coarse adjustment and random modulation for fine adjustment, thereby reducing EMI in charge pump circuits.

[0006] Another objective of this invention is to provide a hybrid modulation method for suppressing EMI in motor drive chips. Periodic modulation is used as coarse tuning to change the spread spectrum range, while random modulation is used as fine tuning to change the edge delay to slow down the switching edge speed. The two can be performed simultaneously, saving area.

[0007] To achieve the above objectives, this invention provides a hybrid modulation method for suppressing EMI in motor drive chips, used to reduce EMI in charge pump circuits, comprising the following steps:

[0008] Step S1: The oscillation circuit connected to the charge pump circuit combines periodic modulation and random modulation to perform hybrid modulation. Periodic modulation is used as coarse adjustment to modulate the charging and discharging current of the oscillation circuit with a triangular wave signal, thereby obtaining a periodically changing oscillation frequency. Random modulation is used as fine adjustment to adjust the output signal of the oscillation circuit. Based on the coarse adjustment, the oscillation circuit is made to jitter at a certain frequency edge, and the delay is randomly changed to slow down the switching edge speed. Finally, in the output oscillation signal, the peak energy concentrated at the switching frequency and harmonic frequency is dispersed to the surrounding frequency band, thereby reducing the energy peak value concentrated at the switching frequency and each harmonic point, so as to reduce the EMI value.

[0009] Step S1.1: In hybrid modulation, let the frequency of periodic modulation be fm1 and the frequency of random modulation be fm2, then the oscillation signal output after hybrid modulation is:

[0010]

[0011] Where A is the carrier amplitude, ω c ω is the carrier frequency. m1 ω is the frequency of the periodically modulated signal. m2 The frequency of the randomly modulated signal;

[0012] Step S1.2: The spectrum obtained after performing a Fourier transform on the oscillating signal is as follows:

[0013]

[0014] Where 2π(fm2+fm1)=a, 2π(fm2-fm1)=b, 1 / 4πfm1=k, thus obtaining the frequency spacing of the hybrid modulation as ±n(fm2+fm1), ±n(fm2-fm1), where:

[0015] If fm2 << fm1, then the frequency interval (can) be the same as nfm1, thus obtaining a more diverse power spectrum with a smaller frequency interval and a smaller fundamental frequency amplitude, resulting in a greater reduction in peak value.

[0016] As a further preferred embodiment of the above technical solution, in step S1, for periodic modulation:

[0017] The modulation current generating circuit of the oscillation circuit receives the control signal generated by the periodic signal generating circuit to control the on / off state of each modulation current branch, thereby generating a periodically changing current signal. These signals are then superimposed to produce a periodically changing charging / discharging current I. OSC The signal provides bias current to the comparator circuit of the oscillation circuit;

[0018] The comparator circuit takes the voltage value of the charging capacitor as the positive input and the reference voltage as the negative input, and then charges and discharges the charging capacitor (C1) continuously through comparison, thereby generating an oscillation signal at a predetermined frequency.

[0019] As a further preferred embodiment of the above technical solution, in step S1, for random modulation:

[0020] The random delay circuit of the oscillation circuit receives the control signal generated by the random signal generation circuit to control the on / off state of each delay branch, thereby adjusting the oscillation signal output by the comparator circuit. This causes the oscillation circuit to jitter at a certain frequency based on the coarse adjustment, and randomly changes the delay to slow down the switching edge speed.

[0021] As a further preferred technical solution to the above technical solution, the specific implementation is as follows: Periodic modulation is achieved through the modulation of the current generation circuit and the comparator circuit.

[0022] The charging current is equal to the discharging current by the modulation current generation circuit. The initial voltage of the charging capacitor C1 is 0, and the output signal Vout of the comparator U1 is low. As a result, switch S1 is turned on and switch S2 is turned off. Then the charging and discharging current IOSC signal charges the charging capacitor C1. At the same time, switch S3 is turned on and switch S4 is turned off. The negative terminal of the comparator U1 selects VrefH.

[0023] When the voltage on the charging capacitor C1 is greater than VrefH, the output signal Vout is high, so that switch S1 is closed and switch S2 is turned on. The charging and discharging current IOSC signal discharges the charging capacitor C1. At the same time, switch S3 is closed and switch S4 is turned on, and the negative terminal of comparator U1 selects VrefL.

[0024] When the charging capacitor C1 discharges to below VrefL, the output signal Vout turns low. Then the charging capacitor C1 is recharged, which generates an oscillation signal of the required frequency (at this point, it has only undergone coarse adjustment and has not yet been finely adjusted by the random delay circuit).

[0025] As a further preferred technical solution to the above technical solution, the random modulation of the random delay circuit is specifically implemented as follows:

[0026] The random signal is implemented using a linear feedback shift register (LFSR). Fine-tuning is performed at the output of the comparator circuit (output signal Vout). The load size is randomly selected, which changes the delay to slow down the switching edge speed and reduce the change in edge dV / dt, thereby reducing the large current spike caused by the instantaneous opening of the switch.

[0027] As a further preferred technical solution to the above technical solution, periodic modulation and random modulation share a comparator circuit, realizing hybrid modulation while saving area.

[0028] As a further preferred embodiment of the above technical solution, step S1 is followed by:

[0029] Step S2: The level shifting circuit receives the oscillation signal output by the oscillation circuit and converts the oscillation signal in the low voltage domain into an oscillation signal in the high voltage domain, so as to drive the charge pump circuit in the high voltage domain.

[0030] Step S3: The buffer circuit receives the oscillation signal from the high-voltage domain output by the level shift circuit and transmits the oscillation signal to the charge pump circuit after buffering. The buffer circuit limits the peak current flowing through the charge pump circuit (pump capacitor Cf) through a switch of a predetermined size to reduce the EMI value for the second time.

[0031] The beneficial effects of this invention are as follows:

[0032] Spread spectrum is used to reduce EMI in circuits. This technique involves modulating the frequency of the control transistor to spread the energy over a wider frequency band, thereby reducing peak and harmonic radiation emissions. Attached Figure Description

[0033] Figure 1 This is an oscillation circuit diagram of the hybrid modulation method for suppressing EMI applied to motor drive chips according to the present invention.

[0034] Figure 2 This is a level shifting circuit diagram of the hybrid modulation method for suppressing EMI applied to motor drive chips according to the present invention.

[0035] Figure 3 This is a buffer circuit diagram of the hybrid modulation method for suppressing EMI applied to motor drive chips according to the present invention.

[0036] Figure 4A This is a circuit diagram before and after modulation of the hybrid modulation method for suppressing EMI applied to motor drive chips according to the present invention.

[0037] Figure 4B This is the power spectrum (unmodulated) of a square wave signal with a power of 2K ohms, used in the hybrid modulation method for suppressing EMI in motor drive chips according to the present invention.

[0038] Figure 5A This is the power spectrum after periodic modulation of the hybrid modulation method for suppressing EMI applied to motor drive chips according to the present invention.

[0039] Figure 5B This is a power spectrum after random modulation of the hybrid modulation method for suppressing EMI in motor drive chips according to the present invention.

[0040] Figure 5C This is the power spectrum after periodic modulation and random modulation of the hybrid modulation method for suppressing EMI in motor drive chips according to the present invention.

[0041] Figure 6A This is a schematic diagram of the entire frequency variation of the hybrid modulation method for suppressing EMI applied to motor drive chips according to the present invention.

[0042] Figure 6B This is a schematic diagram of the hybrid modulation method for suppressing EMI applied to motor drive chips according to the present invention. Detailed Implementation

[0043] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0044] In the preferred embodiments of the present invention, those skilled in the art should note that the motor drive chip, charge pump circuit, etc. involved in the present invention can be regarded as prior art.

[0045] Preferred embodiment.

[0046] This invention provides a hybrid modulation method for suppressing EMI in motor drive chips, used to reduce EMI in charge pump circuits, characterized by comprising the following steps:

[0047] Step S1: The oscillation circuit connected to the charge pump circuit combines periodic modulation and random modulation to perform hybrid modulation. Periodic modulation is used as coarse adjustment to modulate the charging and discharging current of the oscillation circuit with a triangular wave signal, thereby obtaining a periodically changing oscillation frequency. Random modulation is used as fine adjustment to adjust the output signal of the oscillation circuit. Based on the coarse adjustment, the oscillation circuit is made to jitter at a certain frequency edge, and the delay is randomly changed to slow down the switching edge speed. Finally, in the output oscillation signal, the peak energy concentrated at the switching frequency and harmonic frequency is dispersed to the surrounding frequency band, thereby reducing the energy peak value concentrated at the switching frequency and each harmonic point, so as to reduce the EMI value.

[0048] It is worth mentioning that the traditional time-domain signal after periodic modulation is:

[0049]

[0050] Where A is the carrier amplitude, ωc is the carrier frequency, ωm is the modulation signal frequency, and Δ ωmax For the maximum frequency deviation, βF is the modulation coefficient, such that βF = Δω max / ω m .

[0051] The spectrum obtained by performing a Fourier transform on the above formula is:

[0052]

[0053] Where Jn(βF) is the Bessel function:

[0054]

[0055] As can be seen, the frequency spacing of the propagating carrier signal can become ±nωm, and the amplitude Jn(βF) decreases as βF increases.

[0056] In this invention, step S1.1: In hybrid modulation, let the frequency of periodic modulation be fm1 and the frequency of random modulation be fm2, then the oscillation signal output after hybrid modulation is:

[0057]

[0058] Where A is the carrier amplitude, ω c ω is the carrier frequency. m1 ω is the frequency of the periodically modulated signal. m2 The frequency of the randomly modulated signal;

[0059] Step S1.2: The spectrum obtained after performing a Fourier transform on the oscillating signal is as follows:

[0060]

[0061] Where 2π(fm2+fm1)=a, 2π(fm2-fm1)=b, 1 / 4πfm1=k, thus obtaining the frequency spacing of the hybrid modulation as ±n(fm2+fm1), ±n(fm2-fm1), where:

[0062] If fm2 << fm1, then the frequency interval (can) be the same as nfm1 (the parameter of the traditional modulation method), thus obtaining a more diverse power spectrum with a smaller frequency interval and a smaller fundamental frequency amplitude, thereby obtaining a greater peak reduction.

[0063] The overall block diagram of the proposed hybrid modulation is as follows: Figure 1 As shown in the diagram. First, a coarse adjustment is performed. Iosc is a current signal with a triangular pulse, and the output frequency is adjusted by changing the charging and discharging current of capacitor C. The generated output signal is fed back to control the opening and closing of S1-S4, thus generating a continuously changing oscillating signal. The random signal is implemented using a Linear Feedback Shift Register (LFSR). Fine adjustment is performed at the output, randomly selecting its load size to change its delay, thus slowing down the switching edge speed and reducing the change in dV / dt at the edge, thereby reducing the large current spike caused by the instantaneous opening of the switch. Periodic modulation and random modulation share a comparator circuit, achieving hybrid modulation while saving area. The overall frequency variation diagram is shown in the diagram. Figure 6A As shown, the hybrid modulation is illustrated in the diagram. Figure 6B As shown.

[0064] Specifically, in step S1, for periodic modulation:

[0065] The modulation current generating circuit of the oscillation circuit receives the control signal generated by the periodic signal generating circuit to control the on / off state of each modulation current branch, thereby generating a periodically changing current signal. These signals are then superimposed to produce a periodically changing charging / discharging current I. OSC The signal provides bias current to the comparator circuit of the oscillation circuit;

[0066] The comparator circuit takes the voltage value of the charging capacitor as the positive input and the reference voltage as the negative input, and then charges and discharges the charging capacitor (C1) continuously through comparison, thereby generating an oscillation signal at a predetermined frequency.

[0067] More specifically, in step S1, for random modulation:

[0068] The random delay circuit of the oscillation circuit receives the control signal generated by the random signal generation circuit to control the on / off state of each delay branch, thereby adjusting the oscillation signal output by the comparator circuit. This causes the oscillation circuit to jitter at a certain frequency based on the coarse adjustment, and randomly changes the delay to slow down the switching edge speed.

[0069] Furthermore, the periodic modulation is achieved through the modulation of the current generation circuit and the comparator circuit, specifically implemented as follows:

[0070] The charging current is equal to the discharging current by the modulation current generation circuit. The initial voltage of the charging capacitor C1 is 0, and the output signal Vout of the comparator U1 is low. As a result, switch S1 is turned on and switch S2 is turned off. Then the charging and discharging current IOSC signal charges the charging capacitor C1. At the same time, switch S3 is turned on and switch S4 is turned off. The negative terminal of the comparator U1 selects VrefH.

[0071] When the voltage on the charging capacitor C1 is greater than VrefH, the output signal Vout is high, so that switch S1 is closed and switch S2 is turned on. The charging and discharging current IOSC signal discharges the charging capacitor C1. At the same time, switch S3 is closed and switch S4 is turned on, and the negative terminal of comparator U1 selects VrefL.

[0072] When the charging capacitor C1 discharges to below VrefL, the output signal Vout turns low. Then the charging capacitor C1 is recharged, which generates an oscillation signal of the required frequency (at this point, it has only undergone coarse adjustment and has not yet been finely adjusted by the random delay circuit).

[0073] Furthermore, through random modulation of the random delay circuit, the specific implementation is as follows:

[0074] The random signal is implemented using a linear feedback shift register (LFSR). Fine-tuning is performed at the output of the comparator circuit (output signal Vout). The load size is randomly selected, which changes the delay to slow down the switching edge speed and reduce the change in edge dV / dt, thereby reducing the large current spike caused by the instantaneous opening of the switch.

[0075] Preferably, periodic modulation and random modulation share a single comparator circuit, achieving hybrid modulation while saving area.

[0076] Preferably, after step S1, the method further includes:

[0077] Step S2: The level shifting circuit receives the oscillation signal output by the oscillation circuit and converts the oscillation signal in the low voltage domain into an oscillation signal in the high voltage domain, so as to drive the charge pump circuit in the high voltage domain.

[0078] Step S3: The buffer circuit receives the oscillation signal from the high-voltage domain output by the level shift circuit and transmits the oscillation signal to the charge pump circuit after buffering. The buffer circuit limits the peak current flowing through the charge pump circuit (pump capacitor Cf) through a switch of a predetermined size to reduce the EMI value for the second time.

[0079] The principle of this invention is as follows:

[0080] This invention primarily reduces EMI in circuits through two methods. One method involves modulating the frequency of the control switch to disperse the peak energy concentrated at the switching frequency and harmonic frequencies across the surrounding frequency band, thereby reducing the energy peaks at the switching frequency and each harmonic point, and thus lowering the EMI value. Figure 4A As shown;

[0081] For a more convenient and intuitive comparison, the power spectrum of a 2kHz square wave signal is shown below. Figure 4B As shown, the waveforms simulated using MATLAB were compared between periodic modulation and random modulation, and the results are as follows. Figure 5A and 5B As shown, under the same conditions, random modulation is more effective than periodic modulation. Therefore, this paper employs a combined approach of periodic and random modulation to reduce EMI in the circuit. Figure 5C As shown in the power spectrum comparison above, it can be seen that the combined method significantly reduces EMI.

[0082] Another approach is to limit the magnitude of the charging and discharging current of the capacitor, that is, to limit the peak value of di / dt flowing through the capacitor, thereby reducing EMI.

[0083] The novel spread spectrum clock circuit includes an oscillator circuit, a level shifter circuit, and a buffer circuit. For example... Figure 1 As shown, the specific oscillation circuit implementation of this invention mainly consists of three parts: a modulation current generation circuit, a comparator circuit, and a random delay circuit. The control signals Q0-Q3 in the modulation current generation circuit are generated by a periodic signal generation circuit. Its output signal can vary from 0000 to 1111, thus controlling the on / off state of a certain current path, thereby generating a periodically changing current signal, which is then superimposed on I1 to generate a periodically changing charging / discharging current IOSC(I OSCThe signal provides bias current to the comparator. The periodic signal generation circuit consists of a 4-bit adder and a D flip-flop, generating modulation signals Q0-Q3. The control signals Q4-Q7 in the random delay circuit are generated by the random signal generation circuit, where the capacitance values ​​of C2-C5 are 1:2:4:8. The random signal generation circuit generates Q4-Q7 to control the on / off state of a certain current path, adjusting the oscillator's output signal. This, in turn, causes edge jitter at a certain frequency based on coarse adjustment, randomly changing its delay to slow down the switching edge speed. The pseudo-random signal selection is generated by a 4-bit linear feedback shift register and a feedback network.

[0084] The working process is as follows: The charging current is set equal to the discharging current (IOSC above switch S1 and IOSC below switch S2 are equal). Initially, the voltage across the capacitor is 0, and VOUT (Vout) is low, so S1 is on and S2 is off. IOSC charges capacitor C1, while S3 is on and S4 is off, and the negative terminal of the comparator is selected as VrefH. When the voltage across the capacitor is greater than VrefH, Vout is high, at which point S1 is off and S2 is on. IOSC discharges capacitor C1, while S3 is off and S4 is on, and the negative terminal of the comparator is selected as VrefL. When the capacitor discharges below VrefL, the VOUT signal goes low again. The capacitor is then recharged, and this cycle repeats to generate the desired frequency oscillation signal.

[0085] Figure 2 As a level shifting circuit, since the previously mentioned oscillation signal is in the low-voltage domain and cannot drive the charge pump in the high-voltage domain, a level shifting circuit is needed to raise the oscillation signal to the high-voltage domain. Figure 3 As an output buffer circuit, the oscillation signal is output to the pump capacitor Cf of the subsequent charge pump through the buffer circuit, and at the same time controls the conduction and cutoff of switching transistors Q8 and Q9. MP5 and MN12 are small-sized transistors, mainly to limit the peak value of di / dt flowing through the capacitor and reduce EMI.

[0086] It is worth mentioning that the technical features such as motor drive chips and charge pump circuits involved in this patent application should be regarded as prior art. The specific structure, working principle, and possible control methods and spatial arrangement of these technical features can be adopted using conventional choices in the field, and should not be regarded as the inventive point of this patent. This patent will not be further elaborated in detail.

[0087] For those skilled in the art, modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the protection scope of this invention.

Claims

1. A hybrid modulation method for suppressing EMI applied to motor drive chips, used to reduce EMI in charge pump circuits, characterized in that, Includes the following steps: Step S1: The oscillation circuit connected to the charge pump circuit combines periodic modulation and random modulation to perform hybrid modulation. Periodic modulation is used as coarse adjustment to modulate the charging and discharging current of the oscillation circuit with a triangular wave signal, thereby obtaining a periodically changing oscillation frequency. Random modulation is used as fine adjustment to adjust the output signal of the oscillation circuit. Based on the coarse adjustment, the oscillation circuit is made to jitter at a certain frequency edge, and the delay is randomly changed to slow down the switching edge speed. Finally, in the output oscillation signal, the peak energy concentrated at the switching frequency and harmonic frequency is dispersed to the surrounding frequency band, thereby reducing the energy peak value concentrated at the switching frequency and each harmonic point, so as to reduce the EMI value. Step S1.1: In hybrid modulation, let the frequency of periodic modulation be... The frequency of random modulation is The oscillation signal output after hybrid modulation is: ； Where A is the carrier amplitude. For carrier frequency, The frequency of the periodically modulated signal. The frequency of the randomly modulated signal; Step S1.2: The spectrum obtained after performing a Fourier transform on the oscillating signal is as follows: ； in, , , Thus, the frequency spacing of the hybrid modulation is obtained as ,in: if Then the frequency interval and The same applies, resulting in a more diverse power spectrum with reduced frequency spacing and a smaller fundamental frequency amplitude, thus leading to a greater reduction in peak value; In step S1, for random modulation: The random delay circuit of the oscillation circuit receives the control signal generated by the random signal generation circuit to control the on / off state of each delay branch, thereby adjusting the oscillation signal output by the comparator circuit. This allows the oscillation circuit to jitter at a certain frequency based on the coarse adjustment, and randomly changes the delay to slow down the switching edge speed. In step S1, for periodic modulation: The modulation current generating circuit of the oscillation circuit receives the control signal generated by the periodic signal generating circuit to control the on / off state of each modulation current branch, thereby generating a periodically changing current signal. These signals are then superimposed to produce a periodically changing charging / discharging current I. OSC The signal provides bias current to the comparator circuit of the oscillation circuit; The comparator circuit takes the voltage value of the charging capacitor as the positive input and the reference voltage as the negative input, and then continuously charges and discharges the charging capacitor through comparison, thereby generating an oscillation signal at a predetermined frequency.

2. The hybrid modulation method for suppressing EMI applied to a motor drive chip according to claim 1, characterized in that, The specific implementation involves periodic modulation via a modulation current generation circuit and a comparator circuit: The charging current is made equal to the discharging current by the modulation current generation circuit. The initial voltage of the charging capacitor C1 is 0, and the output signal Vout of the comparator U1 is low. As a result, switch S1 is turned on and switch S2 is turned off. Then the charging and discharging current IOSC signal charges the charging capacitor C1. At the same time, switch S3 is turned on and switch S4 is turned off. The negative terminal of comparator U1 selects VrefH. When the voltage on the charging capacitor C1 is greater than VrefH, the output signal Vout is high, so that switch S1 is closed and switch S2 is turned on, and the charging and discharging current IOSC signal discharges the charging capacitor C1. At the same time, switch S3 is closed and switch S4 is turned on, and the negative terminal of comparator U1 selects VrefL. When the charging capacitor C1 discharges to below VrefL, the output signal Vout turns low. Then the charging capacitor C1 is recharged, thereby generating an oscillation signal of the required frequency.

3. The hybrid modulation method for suppressing EMI applied to a motor drive chip according to claim 2, characterized in that, The specific implementation involves random modulation via a random delay circuit: The random signal is implemented using a linear feedback shift register. Fine-tuning is performed at the output of the comparator circuit to randomly select the load size, i.e., change its delay to slow down the switching edge speed and reduce the change in edge dV / dt, thereby reducing the large current spike caused by the instantaneous opening of the switch.

4. The hybrid modulation method for suppressing EMI applied to a motor drive chip according to claim 3, characterized in that, Periodic modulation and random modulation share a single comparator circuit, achieving hybrid modulation while saving area.

5. The hybrid modulation method for suppressing EMI applied to a motor drive chip according to claim 4, characterized in that, Step S1 is followed by: Step S2: The level shifting circuit receives the oscillation signal output by the oscillation circuit and converts the oscillation signal in the low voltage domain into an oscillation signal in the high voltage domain, so as to drive the charge pump circuit in the high voltage domain. Step S3: The buffer circuit receives the oscillation signal from the high-voltage domain output by the level shift circuit and transmits the oscillation signal to the charge pump circuit after buffering. The buffer circuit limits the peak current flowing through the charge pump circuit through a switch of a predetermined size to reduce the EMI value for the second time.

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