CN108233924A - EMI reduction device and method based on phase modulation - Google Patents

Abstract

The invention relates to an EMI reduction device and method based on phase modulation, the device comprises: a phase offset generator for applying a variable amount of phase offset to each modulation cycle of the input signal; a phase modulation read only memory for holding coefficients for determining an amount of phase shift applied at a specific time; and a phase controller for outputting a modulated signal having a phase offset determined by the coefficient. The present invention reduces EMI emissions by phase modulating a clock signal using an optimized delay or phase shift curve to spread the energy spectrum of the clock signal, with a minimum frequency shift to produce a maximally flat spectral response. The overall reliability of the system is increased since the present invention does not use a feedback loop and has a minimum of components.

Description

EMI reduction device and method based on phase modulation

technical field

The present invention relates to the technical field of electromagnetic compatibility, in particular to an EMI (electromagnetic interference, electromagnetic interference) reduction device and method based on phase modulation.

Background technique

Any electrical switching signal, such as voltage or current, is a major source of electromagnetic interference (EMI) for many digital electronic devices. EMI generated by these electronic devices must be suppressed to avoid interference with other electronic devices and to meet FCC regulations. Traditional methods of reducing EMI include the use of "passive" components such as metal shields, chokes, ferrite beads, resistors, and capacitors. A recent trend has been to utilize an "active" approach, where peak energy concentrated in a narrow band is distributed over a wider frequency band. This technique is commonly referred to as spread spectrum modulation.

The spread spectrum method is mainly based on frequency modulation implemented with a phase-locked loop. Other implementations include the use of switched delay elements inserted in the signal path. These approaches are limited by the inability to physically achieve extremely small frequency offsets in the offending signal and provide substantial EMI reduction benefits.

FIG. 1 shows a block diagram of an active EMI (spread spectrum) reduction device based on a phase-locked loop (PLL). As shown in Figure 1, a PLL-based architecture is implemented using a feedback loop network of multiple elements including counters, voltage- or current-controlled oscillators, phase comparators, and filters. Failure of any element of the circuit will result in catastrophic failure. Also, jitter from the PLL can cause large frequency offsets.

Contents of the invention

In view of the above problems, the present invention does not use a feedback loop but phase modulates the clock signal by using an optimized delay or phase offset profile to spread the energy spectrum of the clock signal, thereby reducing EMI emissions, wherein the minimum frequency offset is utilized to produce the most flat spectral response. Since the invention does not use a feedback loop and has a minimum of components, the overall reliability of the system is increased.

According to an aspect of the present invention, a kind of EMI reduction device based on phase modulation is provided, comprising:

a phase offset generator for applying a variable phase offset to each modulation cycle of the input signal;

a phase modulation read-only memory for storing coefficients determined when a phase offset is applied at a particular time; and

a phase controller for outputting a modulated signal with a phase offset determined by the coefficient.

In the EMI reduction device based on phase modulation, the modulated signal has a minimum phase shift as low as +/-0.05% and a modulation ratio greater than 1.

In the EMI reduction device based on phase modulation, the phase offset generator includes: a delay line composed of a plurality of current-limited buffers, wherein, by changing the amount of current fed to each current-limited buffer to change the phase offset.

The described EMI reduction device based on phase modulation, the phase offset generator includes:

a variable load element disposed in the path of the input signal for varying the slope of the input signal by varying the load; and

A buffer for recovering the steep edge rate of the slope-changed signal and delaying it relative to the preceding edge to change the phase offset.

In the EMI reduction device based on phase modulation, the variable load element includes: a capacitive element, a resistive element, an inductive element or any combination thereof.

According to the EMI reduction device based on phase modulation, the phase offset generator includes: a tapped delay line composed of a plurality of individual delay elements and having a plurality of stages of independent access, wherein the delay element is controlled at any stage to Change the phase offset.

In the EMI reduction device based on phase modulation, the phase modulation read-only memory includes: a look-up table, and the look-up table is provided with a control word for determining the coefficient of the phase offset applied at a specific moment.

According to the EMI reduction device based on phase modulation, the phase modulation read-only memory includes: a read-only memory architecture with rows and columns whose components are selected by addresses of the read-only memory.

In the EMI reduction device based on phase modulation, the rate of change of the coefficient is changed by a counter, and the counter provides an address to the phase modulation read-only memory, and the modulation rate of the modulation signal is obtained by the following formula:

Fm=Fin/(D×N)

Among them, Fm is the modulation rate, Fin is the input frequency, D is the input divisor, N is the maximum count value of the ROM counter, and it is assumed that the ROM counter counts from 1 to N sequentially.

In the EMI reduction device based on phase modulation, the calculation method of the modulation ratio is: modulation ratio β=Δf/Fm, where Δf is the total frequency deviation formed on the input frequency Fin, and Fm is the modulation frequency; the The maximum modulation ratio is 2.

According to another aspect of the present invention, a kind of EMI reduction method based on phase modulation is provided, comprising:

Applying a variable phase offset to each modulation cycle of the input signal via a phase offset generator;

by means of a phase modulation read-only memory, storing coefficients determined for applying a phase offset at a particular time instant; and

Through the phase controller, a modulated signal with a phase offset determined by the coefficients is output.

According to an embodiment, said modulated signal has a phase shift down to below +/-0.05% and has a modulation ratio greater than 1.

The EMI reduction method based on phase modulation, wherein the phase offset generator includes: a delay line composed of a plurality of current-limited buffers, wherein, by changing the amount of current to change the phase offset.

The described EMI reduction method based on phase modulation, wherein, the phase offset generator includes:

a variable load element disposed in the path of the input signal for varying the slope of the input signal by varying the load; and

A buffer for recovering the steep edge rate of the slope-changed signal and delaying it relative to the preceding edge to change the phase offset.

In the EMI reduction method based on phase modulation, the variable load element includes: a capacitive element, a resistive element, an inductive element or any combination thereof.

The EMI reduction method based on phase modulation, wherein the phase offset generator includes: a tapped delay line consisting of a plurality of individual delay elements and having a plurality of stages accessed separately, wherein the delay is controlled at any stage by element to change the phase offset.

In the phase modulation-based EMI reduction method, wherein the phase modulation read-only memory includes: a look-up table, the look-up table is provided with a control word for determining the coefficient of the phase offset applied at a specific moment.

In the phase modulation-based EMI reduction method, the phase modulation read-only memory includes: a read-only memory architecture having rows and columns whose components are selected by addresses of the read-only memory.

The EMI reduction method based on phase modulation, wherein, the rate of change of the coefficient is changed by a counter, and the counter provides an address to the phase modulation read-only memory, and the modulation rate of the modulation signal is obtained by the following formula out:

Fm=Fin/(D×N)

Among them, Fm is the modulation rate, Fin is the input frequency, D is the input divisor, N is the maximum count value of the ROM counter, and it is assumed that the ROM counter counts from 1 to N sequentially.

The described EMI reduction method based on phase modulation, wherein the calculation method of the modulation ratio is: modulation ratio β=Δf/Fm, wherein Δf is the total frequency deviation formed on the input frequency Fin, and Fm is the modulation frequency; The maximum modulation ratio is 2.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the description, and are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention.

FIG. 1 is a block diagram of an active EMI reduction device based on a phase-locked loop (PLL) (using a spread spectrum method) in the prior art.

FIG. 2 is a block diagram of an EMI reduction device based on phase modulation according to an embodiment of the present invention.

Fig. 3 is a schematic diagram showing an output signal after an input signal is modulated by the EMI reduction device based on phase modulation according to an embodiment of the present invention.

FIG. 4 is a block diagram of an embodiment of a phase offset generator of an EMI reduction device based on phase modulation according to an embodiment of the present invention.

FIG. 5 is a block diagram of another embodiment of a phase offset generator of a phase modulation based EMI reduction apparatus according to an embodiment of the present invention.

FIG. 6 is a block diagram of a phase modulation ROM of a phase modulation based EMI reduction device according to an embodiment of the present invention.

Fig. 7 is a spectrum diagram of an unmodulated clock signal.

FIG. 8 is a frequency spectrum diagram of a clock signal modulated by the phase modulation-based EMI reduction apparatus according to an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings.

The embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention. And in the case of no conflict, the features in the embodiments of the present invention can be combined with each other, and the formed technical solutions are all within the protection scope of the present invention.

FIG. 2 shows a block diagram of an EMI reduction device based on phase modulation according to an embodiment of the present invention. As shown in Figure 2, the EMI reduction device based on phase modulation of this embodiment includes:

a phase offset generator 201, configured to apply a variable phase offset to each modulation cycle of the input signal;

a phase modulation ROM 202 for storing coefficients used to determine the amount of phase offset to apply at a particular moment; and

a phase controller 203, configured to output a modulated signal having a phase offset determined by a coefficient,

Among them, the output modulation signal has a very small phase shift, for example, as low as +/-0.05%, and in more specific cases, the phase shift can be lower than +/-0.05%, for the case of greater than +/-0.05% , can also achieve phase modulation control, and the output modulation signal has a modulation ratio greater than 1, thereby providing excellent EMI reduction.

Further, FIG. 3 shows the output signal after the input signal is modulated by the EMI reduction device based on phase modulation according to the embodiment of the present invention. As shown in Figure 3, the period of the input signal is T, after being modulated by the EMI reduction device of the present invention, the output signal increases a small amount of change δt every several cycles, in other words, the output modulated signal has a very small phase shift and has Modulation ratios greater than 1, thus providing excellent EMI reduction.

The calculation of the modulation ratio is specifically described below.

First, the frequency offset Δf is calculated from the phase offset φ(t) and the modulation rate Fm. where T is the period of the signal and δT is the period offset (over the half modulation cycle).

Phase offset φ(t)=δT/T

Tm = modulation period = 1/Fm

(on half modulation cycle) frequency offset Δf = φ(t)/(Tm/2)

Frequency offset (over a complete modulation cycle) Δf = (2*φ(t))/Tm

Frequency offset (over a complete modulation cycle) Δf = (2*δT/T)/Tm

Frequency offset (over a complete modulation cycle) Δf = (2*δT)/(T*Tm)

N is the divisor of the modulation rate, that is, the maximum count value of the ROM counter.

Tm=N*T*R, where R is the length of the phase offset ROM, then

(over a complete modulation cycle) frequency offset Δf=(2*δT)/(N*R*T^2)

Among them, the controllable variables are: δT, N and R, then

Modulation ratio β=Δf/Fm, where Fm=1/Tm, where Δf is the total frequency deviation formed on the input frequency Fin, then

β=Δf*Tm, combined with the above equation, then

β=(2*δT)/T

where, for broadband modulation β>>1, and

At full cycle delay, Maxβ=2*T/T=2.

FIG. 4 shows a block diagram of an embodiment of a phase offset generator of an EMI reduction device based on phase modulation according to an embodiment of the present invention. As shown in Figure 4, in this embodiment, the phase offset generator includes a delay line composed of a series of current-limited buffers 401-403, the input signal is fed into the delay line, and the propagation time of each buffer is determined by the feed current flow control to this buffer. By varying the current, the delay is varied, resulting in modulation of the delay.

FIG. 5 shows a block diagram of another embodiment of a phase offset generator of a phase modulation-based EMI reduction device according to an embodiment of the present invention. As shown in Figure 5, in this embodiment, the phase offset generator includes:

The variable load element 501 is arranged in the path of the input signal, and is used to change the slope of the input signal by changing the load; and

The buffer 502 is used to restore the steep edge rate of the signal whose slope changes and generate a delay relative to the preceding edge, so as to change the phase offset.

In this embodiment, the variable load element is a capacitive element, however, the present invention is not limited thereto, and the variable load element may also be a resistive element, an inductive element, or a combination of all three or any two. By varying the load presented to the input signal, the delay or phase offset between successive edges also changes, resulting in delayed modulation.

In the above two embodiments, a digital-to-analog converter can also be used in conjunction with analog control to digitally control the delay or the analog variation of the load, respectively.

In another embodiment, the phase offset generator may also include a tapped delay line consisting of a plurality of individual delay elements and having individually accessed stages, wherein the phase offset is varied by controlling the delay elements at any stage . For example, it is possible to have a 10-stage delay line, where each delay stage is equal to, for example, 1 second. Any level can be chosen to get 1, 2, 3, etc. up to 10 seconds of delay. If we tap at level 3, we get a 3 second delay.

Hereinafter, the phase offset read only memory (ROM) of the phase modulation based EMI reduction device according to the embodiment of the present invention will be specifically described.

The phase modulation ROM holds the sequence of coefficients and the desired phase offset or delay to be applied to the input signal (the signal to be phase modulated). In an embodiment, the phase modulation ROM may include a look-up table, where the delay is selected by a control word supplied to the look-up table. This can be implemented as a combinational logic block or by any other means.

In another embodiment, the phase modulation ROM may comprise a conventional ROM architecture with individual elements selected by the ROM address in rows and columns. Note that an extension to either of these methods would introduce the ability to dynamically program these ROM coefficients by programming the interface or programming at any stage of circuit fabrication. This will allow further optimization of the device to suit requirements.

The total maximum phase deviation experienced by the input signal determines the maximum phase deviation and thus the maximum frequency deviation of the modulated signal. The rate at which the phase modulation ROM provides phase offset values determines the modulation rate of the modulated signal. The rate at which the ROM coefficients change can be controlled in a number of ways, one of which is through a counter that provides an "address" to the ROM.

Referring to FIG. 6 , it shows a block diagram of a phase modulation read only memory (ROM) of a phase modulation based EMI reduction device according to an embodiment of the present invention. As shown in Figure 6, the counter is clocked by the input signal and the modulation rate is calculated as follows:

Fm=Fin/(D×N)

Among them, Fm is the modulation rate, Fin is the input frequency, D is the input divisor, N is the maximum count value of the ROM counter, and it is assumed that the ROM counter counts from 1 to N sequentially.

Fig. 7 shows a spectrum diagram of an unmodulated clock signal. FIG. 8 shows a spectrum diagram of a clock signal modulated by the phase modulation-based EMI reduction apparatus according to an embodiment of the present invention. As shown in Figure 7, the unmodulated clock signal is normalized to 0dB, while in Figure 8, the peak amplitudes of the harmonics of the sinusoidal phase modulated clock signal are all suppressed, for example, at frequency f0, the peak amplitude 6dB down.

According to another aspect of the present invention, a kind of EMI reduction method based on phase modulation is also provided, comprising:

Applying a variable phase offset to each modulation cycle of the input signal via a phase offset generator;

storing coefficients for determining the amount of phase offset to apply at a particular instant, via a phase modulation read-only memory; and

Through the phase controller, a modulated signal with a phase offset determined by the coefficients is output.

The modulated signal has a minimum phase shift as low as +/-0.05% and has a modulation ratio greater than 1, providing excellent EMI reduction.

In summary, the present invention reduces EMI emissions by phase modulating a clock signal using an optimized delay or phase offset profile to spread the energy spectrum of the clock signal, wherein the smallest frequency offset is utilized to produce the largest flat spectral response. Since the invention does not use a feedback loop and has a minimum of components, the overall reliability of the system is increased.

Although the embodiments disclosed in the present application are as above, the content described is only the embodiments adopted for the convenience of understanding the present application, and is not intended to limit the present application. Anyone skilled in the technical field to which this application belongs can make any modifications and changes in the form and details of implementation without departing from the spirit and scope disclosed in this application, but the protection scope of this application remains the same. The scope defined by the appended claims shall prevail.

Claims (20)

1. A kind of EMI reducing device based on phase modulation, it is characterized in that, comprising: a phase offset generator for applying a variable phase offset to each modulation cycle of the input signal; a phase modulation read-only memory for storing coefficients determined when a phase offset is applied at a particular time; and a phase controller for outputting a modulated signal with a phase offset determined by the coefficient. 2 . The EMI reduction device based on phase modulation according to claim 1 , wherein the modulation signal has a minimum phase shift as low as +/-0.05% or less and has a modulation ratio greater than 1. 3 . 3. The EMI reduction device based on phase modulation according to claim 1, wherein the phase offset generator comprises: a delay line composed of a plurality of current-limited buffers, wherein, by changing the feed to The amount of current in each current-limited buffer changes the phase offset. 4. The EMI reduction device based on phase modulation according to claim 1, wherein the phase offset generator comprises: a variable load element disposed in the path of the input signal for varying the slope of the input signal by varying the load; and A buffer for recovering the steep edge rate of the slope-changed signal and delaying it relative to the preceding edge to change the phase offset. 5. The EMI reduction device based on phase modulation according to claim 4, wherein the variable load element comprises: a capacitive element, a resistive element, an inductive element or any combination thereof. 6. The EMI reduction device based on phase modulation according to claim 1, wherein the phase offset generator comprises: a tapped delay line consisting of a plurality of individual delay elements and having a plurality of stages of independent access , where the phase offset is varied by controlling the delay elements at any stage. 7. The EMI reduction device based on phase modulation according to claim 1, wherein the phase modulation read-only memory comprises: a look-up table, the look-up table is provided with a control word for determining the Factor for the phase offset. 8 . The EMI reduction device based on phase modulation according to claim 1 , wherein the phase modulation read-only memory comprises: a read-only memory architecture having rows and columns whose elements are selected by addresses of the read-only memory. 9. The EMI reduction device based on phase modulation according to claim 7 or 8, wherein the rate at which the coefficient changes is changed by a counter, and the counter provides an address to the phase modulation ROM, so The modulation rate of the modulated signal is given by: Fm=Fin/(D×N) Among them, Fm is the modulation rate, Fin is the input frequency, D is the input divisor, N is the maximum count value of the ROM counter, and it is assumed that the ROM counter counts from 1 to N sequentially. 10. The EMI reduction device based on phase modulation according to claim 2, wherein the calculation method of the modulation ratio is: modulation ratio β=Δf/Fm, where Δf is the total frequency formed on the input frequency Fin Deviation, Fm is the modulation frequency; the maximum value of the modulation ratio is 2. 11. A method for reducing EMI based on phase modulation, comprising: Applying a variable phase offset to each modulation cycle of the input signal via a phase offset generator; by means of a phase modulation read-only memory, storing coefficients determined for applying a phase offset at a particular time instant; and Through the phase controller, a modulated signal with a phase offset determined by the coefficients is output. 12. The EMI reduction method based on phase modulation according to claim 11, wherein said modulated signal has a minimum phase shift as low as +/-0.05% or less and has a modulation ratio greater than 1. 13. The EMI reduction method based on phase modulation according to claim 11, wherein the phase offset generator comprises: a delay line composed of a plurality of current-limited buffers, wherein, by changing the current The amount of current limited to the snubber to change the phase offset. 14. The EMI reduction method based on phase modulation according to claim 11, wherein the phase offset generator comprises: a variable load element disposed in the path of the input signal for varying the slope of the input signal by varying the load; and A buffer for recovering the steep edge rate of the slope-changed signal and delaying it relative to the preceding edge to change the phase offset. 15. The method for reducing EMI based on phase modulation according to claim 14, wherein the variable load element comprises: a capacitive element, a resistive element, an inductive element or any combination thereof. 16. The EMI reduction method based on phase modulation according to claim 11, wherein the phase offset generator comprises: a tapped delay line consisting of a plurality of individual delay elements and having a plurality of stages of independent access , where the phase offset is varied by controlling the delay elements at any stage. 17. The EMI reduction method based on phase modulation according to claim 11, characterized in that, the phase modulation read-only memory comprises: a look-up table, the look-up table is provided with a control word for determining the Factor for the phase offset. 18. The method for reducing EMI based on phase modulation according to claim 11, wherein the phase modulation ROM comprises: a ROM architecture having rows and columns where each element is selected by an address of the ROM. 19. The EMI reduction method based on phase modulation according to claim 17 or 18, wherein the rate at which the coefficient changes is changed by a counter, and the counter provides an address to the phase modulation ROM, so The modulation rate of the modulated signal is given by: Fm=Fin/(D×N) Among them, Fm is the modulation rate, Fin is the input frequency, D is the input divisor, N is the maximum count value of the ROM counter, and it is assumed that the ROM counter counts from 1 to N sequentially. 20. The method for reducing EMI based on phase modulation according to claim 12, wherein the calculation method of the modulation ratio is: modulation ratio β=Δf/Fm, wherein Δf is the total formed on the input frequency Fin Frequency deviation, Fm is the modulation frequency; the maximum value of the modulation ratio is 2.