JP2003084857A - Clock signal transmitting method, clock signal transmitting and receiving device, and image display applied apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To theoretically prevent a fundamental wave and a harmonic component of a clock signal from generating in an EMI measuring band, in the transmission system of the signal from a transmitting part to a receiving part. SOLUTION: In the clock signal transmitting part 9, the clock signal having a fundamental wave frequency fclk which is generated in a clock signal generator is given to a 1/N frequency divider 11, and the frequency is divided to fclk/N. A carrier wave having a frequency fc is PWM-modulated by using a signal with this frequency fclk/N in a PWM modulator 13. At this time, fc is set so that fc-fclk/N>fmax is formed in relation to the maximum frequency fmax in the EMI measuring band B. The maximum fluctuation of the pulse width of the carrier wave in the PWM modulation is kept at about several % of the cycle of the carrier wave. A phase lock loop is operated in a clock signal receiving part 15, and the clock signal of the frequency fclk is reproduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to radiated electromagnetic noise (hereinafter referred to as EMI) generated from a clock signal transmission system in various electronic devices.
That is) related to the technology.

[0002]

2. Description of the Related Art In recent years, with the increase in operation speed of electronic equipment,
The frequency of the clock signal for operating it is also increasing. The EMI caused by the fundamental wave and higher harmonics of the clock signal causes peripheral devices to malfunction or deteriorates performance, and suppression thereof is a major issue in product development.

Currently, EM in clock signal transmission systems.
As one of the techniques for suppressing I, a low voltage differential transmission method has been put into practical use, and this method will be described below. FIG. 5 is a block diagram showing the principle of the above-mentioned low voltage differential transmission method. In the figure, the clock signal transmitter 1 has a clock signal generator 2 and a differential signal driver 3. The differential signal driver 3 is a driver that converts the clock signal from the clock signal generator 2 into a low voltage differential signal and outputs it.

The transmission lines 4 and 5 are lines for transmitting the output signal of the differential signal driver 3 to the clock signal receiving section 6, the transmission line 4 for in-phase signals and the transmission line 5 for anti-phase signals. . The clock signal receiving unit 6 is the clock signal transmitting unit 1
The receiving unit receives the differential clock signal from the. The clock signal receiving unit 6 has a differential amplifier 7 and an internal circuit 8. The differential amplifier 7 is an amplifier that converts the received differential clock signal into the original clock signal. The internal circuit 8 is a circuit that operates by receiving the clock signal from the differential amplifier 7.

FIG. 6 is a spectrum diagram showing the frequency components of the clock signal and the EMI measurement band in the transmission system from the clock signal transmitter 1 to the clock signal receiver 2. In the figure, B indicates the EMI measurement band. fmax represents the highest frequency in the EMI measurement band B, and fmin represents the lowest frequency in the EMI measurement band B. fclk represents the basic frequency of the clock signal generated by the clock signal generator 2, and 2fclk, 3fclk, ..., Nf
clk, ... Indicates harmonic frequencies of fclk. Further, it is assumed that the fundamental wave frequency fclk and / or the harmonic wave frequency thereof are within the EMI measurement band B.

The operation principle of the low-voltage differential transmission method thus configured will be described below. In the clock signal transmitter 1, the clock signal generated by the clock signal generator 2 is input to the differential signal driver 3. The differential signal driver 3 outputs this clock signal with the same phase and opposite phase,
Converts to a pair of differential signals with amplitude of 200 to 300 mVpp. The in-phase signal is transmitted to the clock signal receiving unit 6 through the transmission line 4 and the in-phase signal is transmitted through the transmission line 5.

In the clock signal receiving unit 6, the differential amplifier 7
Then, of the pair of differential signals, the phase of the opposite-phase signal is inverted, added to the other in-phase signal, and amplified. The pair of differential signals thus input is converted into the original clock signal. The converted clock signal is input to the internal circuit 8 to operate the internal circuit 8.

[0008]

In the above low voltage differential transmission method, the transmission of the clock signal from the clock signal transmitting section 1 to the clock signal receiving section 6 is performed with an amplitude of about 200 to 300 mVpp. Therefore, as the signal amplitude is lower, the occurrence of EMI in the transmission system can be suppressed.

However, normally, in clock signal transmission, fclk is several tens of MHz, and the EMI measurement band is also fmin = several tens of MHz and fmax = 1 GHz.
Therefore, the frequency component of the clock signal in the transmission system is generated within the EMI measurement band B as shown in FIG. And the shape of the equipment, the wiring method on the circuit board,
Depending on the component mounting method, the configuration of the power supply, the ground, etc., any of these frequency components resonates with them, and the voltage amplitude increases. Alternatively, some component may act as a transmitting antenna to cause EMI.

The present invention has been made in view of the above conventional problems, and in a clock signal transmission system, the fundamental wave and harmonic components of the clock signal are EMI.
It is an object of the present invention to realize a clock signal transmission method, a clock signal transmission / reception device, and an image display application device that do not occur in principle within a measurement band.

[0011]

According to a first aspect of the present invention, there is provided a clock signal transmitting section for generating a clock signal and frequency-converting the clock signal to generate a transmission clock signal, and the clock signal. A clock signal transmission method in a device comprising a transmission line for transmitting a transmission clock signal output from a transmission unit and a clock signal receiving unit for receiving the transmission clock signal transmitted by the transmission line. , A clock signal is generated by the clock signal transmission unit, and the frequency of the clock signal is divided to extract a low-frequency component, whereby the clock signal is converted into a divided clock signal, and the PWM carrier signal is converted by the divided clock signal PWM-modulate and transmit the PWM-modulated signal as the transmission clock signal to the clock signal receiving unit through the transmission path, The PWM is a lock signal receiving section
The modulated signal is demodulated to reproduce the divided clock signal, a reference clock signal is oscillated using a voltage controlled oscillator circuit, the reference clock signal is divided to generate a divided reference clock signal, and the PWM demodulation is performed. The divided clock signal obtained by the above is input, phase control is performed on the divided reference clock signal, and a reference clock signal synchronized with the divided clock signal is obtained from the voltage controlled oscillation circuit. This is a clock signal transmission method.

According to a second aspect of the present invention, in the clock signal transmitting method according to the first aspect, at least one of the fundamental frequency and the harmonic frequency of the clock signal is within the measurement band of radiated electromagnetic field noise, The difference between the frequency of the PWM carrier signal in the clock signal transmitter and the frequency-divided component of the fundamental frequency of the clock signal is larger than the highest frequency of the measurement band of the radiated electromagnetic field noise. .

According to a third aspect of the present invention, in the clock signal transmitting method according to the first aspect, the maximum change amount of the pulse width of the PWM carrier signal in the clock signal transmitting unit is about several% of the carrier wave period. It is a feature.

According to the invention of claim 4 of the present application, a clock signal is generated and a clock signal transmitting section for generating a transmission clock signal by frequency-converting the clock signal is outputted from the clock signal transmitting section. A clock signal transmission / reception device comprising: a transmission line that transmits a transmission clock signal; and a clock signal reception unit that receives the transmission clock signal transmitted by the transmission line, wherein the clock signal transmission unit comprises: A clock signal generator for generating a clock signal; frequency dividing means for dividing the frequency of the clock signal generated by the clock signal generator to extract a low frequency component to output a divided clock signal; P that performs PWM modulation with the divided clock signal output from the frequency dividing means
And a WM modulator, wherein the clock signal receiving unit receives the PWM signal received through the transmission line.
L for demodulating the modulated signal and reproducing the divided clock signal
PF and phase synchronization means for generating a reference clock signal having the same frequency as the clock signal generated by the clock signal generator in synchronization with the divided clock signal of the LPF, and the phase synchronization means generated by the phase synchronization means. And an internal circuit that operates with a reference clock signal.

An image display application device according to claim 5 of the present application is characterized by using the clock signal transmission method according to any one of claims 1 to 3.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A clock signal transmission method according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the principle of the clock signal transmission method according to the present embodiment. As shown in the figure, the clock signal transmitter 9 includes a clock signal generator 10,
It is configured to include a 1 / N frequency divider 11, an LPF 12, and a PWM modulator 13.

The 1 / N frequency divider 11 is a clock signal generator 1.
It is a circuit that divides the fundamental frequency of the clock signal generated by 0 into 1 / N and converts it into a divided clock signal. LP
F12 is a low-pass filter that extracts the fundamental wave frequency component of the clock signal divided by the 1 / N divider 11.
The PWM modulator 13 performs pulse width modulation by using the clock signal output from the LPF 12 as a modulation signal,
It is a circuit that generates a transmission clock signal. Transmission line 1
Reference numeral 4 is a transmission line for transmitting the PWM modulation signal output from the PWM modulator 13 to the receiving side.

The clock signal receiving section 15 includes an LPF 16,
Phase comparator (PC) 17, LPF 18, VCO 19, 1
The / N frequency divider 20 and the internal circuit 21 are included. L
The PF 16 is a low-pass filter that extracts a low frequency component of the PWM modulation signal transmitted from the PWM modulator 13.
The phase comparator 17 outputs the output of the LPF 16 and the 1 / N frequency divider 2
It is a circuit that compares the phase with the output of 0 and outputs the phase difference as a phase error signal. The VCO 19 is a voltage controlled oscillator that generates a reference clock signal of frequency fclk based on the output voltage of the LPF 18.

Phase comparator 17, LPF 18, VCO 1
The 9 and 1 / N frequency divider 20 form a phase locked loop and have a function of regenerating the original clock signal from the signal extracted by the LPF 16. The internal circuit 21 is a circuit which operates by receiving the clock signal reproduced by the phase locked loop.

FIG. 2 shows the waveform of the PWM modulation signal in the PWM modulator 13, and FIG. 2 (a) is the waveform of the PWM carrier signal when there is no modulation, where τ is the pulse width and Tc is the period. FIG. 2B shows a waveform when the pulse width of the PWM carrier signal becomes maximum by PWM modulation, and FIG. 2C shows P by PWM modulation.
It is a waveform when the pulse width of the WM carrier signal is minimum. In FIG. 2, Δτ indicates the maximum amount of change in the pulse width, and the broken line portion is the PWM carrier signal waveform at the time of no modulation. Thus, the pulse width of the carrier wave in PWM modulation is τ ± Δ
Change within τ.

FIG. 3 shows a clock signal transmitting method according to the present invention.
FIG. 3 is a spectrum diagram in a transmission system to the H.V., showing frequency components of a PWM modulation signal and an EMI measurement band.
In the figure, B is the EMI measurement band, fmax and fmin are the maximum and minimum frequencies in the EMI measurement band B, and fclk is the fundamental frequency of the clock signal generated by the clock signal generator 10. It is assumed that fclk and / or its harmonic frequency are within the EMI measurement band B. Further, fc is the PWM carrier frequency of the PWM modulator 13.

FIG. 4 shows L in the clock signal receiving section 15.
This is an example of a circuit of the PF 16, and the LPF 16 is composed of a resistor 22 and a capacitor 23.

The operation of the clock signal transmission method having such a configuration will be described. In the clock signal transmitter 9 of FIG. 1, the clock signal generator 10 generates a clock signal. This clock signal is the fundamental frequency fclk
And its harmonics. The 1 / N frequency divider 11 divides the fundamental frequency of the clock signal into 1 / N,
The LPF 12 extracts only the fundamental frequency component fclk / N. The PWM modulator 13 generates a PWM carrier wave of frequency fc, and performs PWM modulation with the signal of frequency fclk / N extracted by the LPF 12. At this time, the frequency fc is
Fc-f for the maximum frequency fmax of the EMI measurement band B
Set so that clk / N> fmax.

The PWM modulation signal generated by the PWM modulator 13 is expressed as follows. P at no modulation
The WM carrier signal vc (t) is expressed by the following equation (1), where Tc is its repetition period and τ is the pulse width during non-modulation.

[Equation 1]

Further, the clock signal of frequency fclk generated by the clock signal generator 10 is 1 / N by the 1 / N frequency divider 11.
The signal vclk (t) when the fundamental wave component is extracted by the LPF 12 is expressed by the following equation (2).

[Equation 2]

When the pulse width τ in the equation (1) is modulated by the signal of the equation (2), τ becomes the equation (3). Here, m is a modulation rate.

[Equation 3] Substituting equation (3) into τ in equation (1), the PWM modulator 1
The PWM modulation signal output from 3 is a signal represented by the equation (4).

[Equation 4]

Formula (4) is the trigonometric function formula shown in Formula (5).

[Equation 5] Is used, it becomes like a formula (6).

[Equation 6] Furthermore, formula (7) of Bessel function

[Equation 7] Thus, when the series expansion of the Bessel function is used, the PWM carrier signal vc (t) at the time of modulation is expressed by the equation (8).

[Equation 8]

Applying the trigonometric formula (9) to this formula (8), vc (t) finally becomes (10)
The signal is expressed by the equation.

[Equation 9]

[Equation 10]

In the equation (10), (a) is a direct current component, and (b) is
Is 1 of the clock signal of frequency fclk generated on the transmission side.
/ N divided signal fundamental wave component, (c) is PWM of frequency fc
The fundamental and harmonic components of the carrier wave, (d) is the primary sideband of the fundamental component and each harmonic component in (c), and (e) is the secondary sideband of each component in (c). The band, (f) represents the third and higher order odd sidebands of each component in (c), and (g) represents the fourth and higher even sidebands of each component in (c).

Here, when n = 1, the trigonometric function in the equation (10) and the part of the Bessel function J in () are (1)
It can be transformed as in equation (1).

[Equation 11]

For example, when Δτ is about 6% of Tc, that is, under the condition of equation (12),

[Equation 12] The value of the equation (11) is about 0.2, and the equation (13) is established from the property of the Bessel function. The value of Δτ / Tc is several%
The expression (13) is sufficiently satisfied.

[Equation 13]

Thus, in the equation (10), the second or higher sideband component in the fundamental wave component fc of the PWM carrier wave,
That is, in the same equation, the following (e) when n = 1 can be approximated by 0.

Similarly, under the condition of equation (12), the second or higher sideband component in the harmonic component of fc, that is, (10)
After (e) in the case of n ≧ 2, the equations (14) and (15) hold due to the nature of the Bessel function.

[Equation 14]

[Equation 15]

Further, the expression after (e) in the expression (10) is 1 / n
And there is a product of each Bessel function Jk (0.2n), n ≧ 2
Then becomes approximately 0. That is, under the condition of the expression (12), the second or higher sideband component in the harmonic component of fc can be approximated by zero. Therefore (1
Equation (0) can be approximated as equation (16).

[Equation 16]

In the equation (16), (h) is a DC component,
(i) is the fundamental wave component of the 1 / N frequency-divided signal of the clock signal of frequency fclk generated on the transmission side, and (j) is P of the frequency fc.
The fundamental wave and harmonic components of the WM carrier, and (k) are the primary sideband components of the fundamental wave and harmonic components in (j).

From the above, the frequency component of the PWM modulation signal output from the PWM modulator 13 is EM as shown in FIG.
I fclk / N on the low frequency side of measurement band B and fc − on the high frequency side
fclk / N, fc, fc + fclk / N, and its harmonic components nfc-fclk / N, nfc, nfc + fclk / N
(N = 2, 3 ...) Exists.

Such a PWM modulation signal is transmitted to the transmission line 1
4 to the LPF 16 in the clock signal receiver 15. Normally, fmin and fmax of the EMI measurement band B are about fmin = 30 MHz and about fmax = 1 GHz, respectively. Therefore, the LPF 16 may have a simple filter configuration including the resistor 22 and the capacitor 23 as shown in FIG. 4, and can extract fclk / N as the divided reference clock signal from the modulation signal. The signal of the extracted frequency fclk / N is input to the phase comparator 17.

Phase comparator 17, LPF 18, VCO 1
In the phase locked loop composed of the 9 and 1 / N frequency divider 20, the VCO 19 oscillates a signal composed of the frequency fclk and its harmonics. The divided clock signal having the frequency fclk / N and the divided reference clock signal obtained by dividing the reference clock signal of the VCO 19 into 1 / N by the 1 / N divider 20 are phase-compared by the phase comparator 17, The output signal (phase error signal) is input to the LPF 18. The LPF 18 deletes the high frequency component of the input signal, generates a DC voltage proportional to the phase difference between both signals input to the phase comparator 17, and outputs the DC voltage to the VCO 19.

The VCO 19 uses this DC voltage to control the phase of the oscillation signal so that the phase of the oscillation signal is synchronized with the phase of the extraction signal of the frequency fclk / N. As a result, the signal output from the VCO 19 is composed of the frequency fclk and its harmonics, and its phase is synchronized with the phase of the extraction signal of the frequency fclk / N. Therefore, the clock signal receiving section 15 reproduces the clock signal whose phase is synchronized with the original clock signal generated by the clock signal generator 10 in the clock signal transmitting section 9. This reproduced clock signal is input to the internal circuit 21 to operate the internal circuit 21.

The above clock signal transmission method can be applied to image display application equipment and portable information terminal equipment. It is assumed that the image display application device includes a PC main body and a display. When the clock signal receiving unit 15 is a liquid crystal display monitor and the display data and the clock signal are transferred from the PC main body to the monitor, the frequency of the electromagnetic wave radiated from the cable (transmission line 14) coupling the two is measured in the EMI measurement band. Can be excluded from.

[0041]

As described above, according to the clock signal transmission method and apparatus of the present invention, the fundamental wave and harmonic components of the clock signal transmission system do not occur in principle within the EMI measurement band. It is possible to suppress the occurrence of EMI due to the clock signal transmission system.

[Brief description of drawings]

FIG. 1 is a block diagram showing the principle of a clock signal transmission method according to an embodiment of the present invention.

FIG. 2 is a waveform diagram of a PWM carrier wave in the PWM modulator according to the present embodiment.

FIG. 3 is a spectrum diagram showing frequency components of a signal output from the clock signal transmission unit of this embodiment and an EMI measurement band.

FIG. 4 is a configuration example of an LPF used in the clock signal receiving section of the present embodiment.

FIG. 5 is a block diagram showing the principle of a conventional clock signal transmission method.

FIG. 6 is a spectrum diagram showing frequency components of a signal output from a conventional clock signal transmitter and an EMI measurement band.

[Explanation of symbols]

9 Clock signal transmitter 10 Clock signal generator 11 1 / N frequency divider 12 LPF 13 PWM modulator 14 Transmission line 15 Clock signal receiver 16 LPF 17 Phase comparator (PC) 18 LPF 19 VCO 20 1 / N frequency divider 21 Internal circuit

Claims (5)

[Claims] 1. A clock signal transmission unit that generates a clock signal and frequency-converts the clock signal to generate a transmission clock signal, and a transmission clock signal output from the clock signal transmission unit. A clock signal transmitting method in a device configured by a transmission line and a clock signal receiving unit that receives the transmission clock signal transmitted by the transmission line, wherein the clock signal transmitting unit generates a clock signal, The frequency of the clock signal is frequency-divided to extract a low-frequency component to be converted into a frequency-divided clock signal, the PWM carrier signal is PWM-modulated by the frequency-divided clock signal, and the PWM-modulated signal is transmitted to the transmission clock. The signal is transmitted to the clock signal receiving unit through the transmission line, and the PWM modulation is performed in the clock signal receiving unit. Signal to regenerate the divided clock signal, oscillate a reference clock signal using a voltage controlled oscillator circuit, divide the reference clock signal to generate a divided reference clock signal, and generate the divided reference clock signal by the PWM demodulation. A clock characterized in that the obtained divided clock signal is input, phase control is performed on the divided reference clock signal, and a reference clock signal synchronized with the divided clock signal is obtained from the voltage controlled oscillator circuit. Signal transmission method. 2. The fundamental frequency of the clock signal and at least one of the harmonic frequencies thereof are within the measurement band of the radiated electromagnetic field noise, and the frequency of the PWM carrier signal in the clock signal transmitter and the fundamental frequency of the clock signal. 2. The clock signal transmission method according to claim 1, wherein a difference between the frequency component and the frequency-divided component is larger than the highest frequency in the measurement band of the radiated electromagnetic field noise. 3. The PWM in the clock signal transmitter
The maximum change in the pulse width of the carrier signal is a few% of the carrier cycle.
The clock signal transmission method according to claim 1, wherein the clock signal transmission method is a degree. 4. A clock signal transmitting unit that generates a clock signal and frequency-converts the clock signal to generate a transmission clock signal, and transmits the transmission clock signal output from the clock signal transmitting unit. A clock signal transmission / reception device comprising: a transmission line; and a clock signal reception unit that receives a transmission clock signal transmitted by the transmission line, wherein the clock signal transmission unit is a clock signal that generates a clock signal. A generator, a frequency dividing unit that divides the frequency of the clock signal generated by the clock signal generator, extracts a low frequency component and outputs a divided clock signal, and a frequency dividing unit that outputs the divided frequency signal. PWM with a circular clock signal
A PWM modulator that performs modulation, the clock signal receiving unit demodulates the PWM modulation signal received through the transmission line to reproduce the divided clock signal, and the LPF, Phase synchronization means for generating a reference clock signal having the same frequency as the clock signal generated by the clock signal generator in synchronization with the divided clock signal of the LPF; and a reference clock signal generated by the phase synchronization means. An internal circuit that operates, and a clock signal transmission / reception device characterized by the above. 5. An image display application device using the clock signal transmission method according to claim 1. Description: