JP4746451B2 - High precision clock trigger continuous delay device - Google Patents

Description

  The present invention relates to a clock signal and trigger signal delay device that can be used in a field where a clock signal or trigger signal synchronized with a reference clock with high accuracy needs to be generated. It can be used for timing control and various trigger timing control of accelerators.

  In recent years, there has been a demand for generating a clock signal and a trigger signal synchronized with a reference clock with high accuracy in the field of experiments using lasers and the field of accelerators (Patent Document 1).

(1) About the delay in the synchronous experiment of the reference clock and the pulse laser In order to investigate the characteristics of the material, an experiment is conducted in which the material is excited with a pulse laser and the excited state is observed with synchrotron radiation. At this time, it is necessary to change the time interval between the pulse laser to be excited and the radiation light to be observed. The emitted light is supplied at a timing synchronized with the reference clock and cannot be changed by the experimenter. Therefore, it is necessary to change the irradiation timing of the pulse laser. In order to control the output timing of the ultrashort pulse laser oscillated by the mode lock method, it is necessary to give the ultrashort pulse laser a trigger signal having a frequency obtained by dividing the light velocity by twice the resonator length. In general, the resonator length is about 1 meter, and as a result, the frequency of the trigger signal is in the megahertz band. A conventional method for giving a time delay to a signal in the megahertz band is as follows.

    a. Cable type delay method. In this method, laser clock cables having different lengths are switched by a mechanical switch. However, with this method, it is difficult to change the setting of a minute delay amount (for example, 5 ps), and pulse laser oscillation becomes unstable temporarily during switching. Furthermore, there is a problem that the delay amount differs from the required setting depending on the switching step.

    b. A method using a trombone delay device. In this method, the amount of delay is varied by mechanically changing the length of the coaxial waveguide. However, this method has a problem that the variable range is narrow.

    c. Method by optical delay. In this method, the light arrival time can be varied with high accuracy by creating an extra folding portion in the optical path of the laser resonator and adjusting the reciprocation distance. However, this method has a problem that, when a large delay is applied, if the accuracy of optical axis adjustment of the optical path is poor, the light spot shifts.

(2) About the delay in the trigger used in the accelerator The trigger signal to the pulse magnet of the accelerator, the pulse high-frequency generator, the monitor device, etc. needs to be synchronized with high accuracy with respect to the reference high-frequency clock. Conventionally, the above-described ab method and the following method are used to generate a trigger signal.

d. Counter type delay device method. In this method, the clock is counted by a logic counter, and a delay trigger signal is output when the set value is reached. However, this method has a problem that a delay amount equal to or less than the clock cycle cannot be set.
JP-A-7-209388

  When a plurality of ultrashort pulse laser light sources are used by being controlled by an external trigger, or when a trigger used in an accelerator power source or the like is controlled, the methods described in the above a, b, c, and d exist conventionally. But each had its own problems. An object of the present invention is to solve such problems by the following method.

  As shown in FIG. 1, the present invention uses an arbitrary delay time for a pulse signal 501 synchronized with a reference clock using a controller 300 and a counter 400 combined with a quadrature modulator (a circuit that provides an arbitrary phase delay) 200. In the method of generating the pulse signal 410 and the delayed clock signal 411 with high accuracy, the control signal input from the controller to the quadrature modulator is continuously changed to continuously generate the pulse signal 410 and the delayed clock signal 411 within the period of the reference clock or exceeding the period. In this method, an arbitrary delay amount is set.

  As shown in FIG. 3, another invention of the present invention uses an input clock to a counter in a method of delaying a start signal 601 continuously with an arbitrarily high accuracy using a counter 400 combined with a quadrature modulator 200. This is a method of realizing a pulse delay circuit having a delay time setting resolution equal to or less than a reference clock cycle with high accuracy by using a signal 216 that has been subjected to phase modulation using a quadrature modulator as a signal.

The present invention solves the above problems by a control operation using the following mathematical formula.
Express basic concepts with simple formulas.
Reference high frequency clock signal

は初期位相である。基準高周波クロック信号に対して時間τだけ遅れた信号波形は And Where f is the frequency,

Is the initial phase. The signal waveform delayed by time τ with respect to the reference high-frequency clock signal is

Given in. The above formula is

だけ遅らせた信号と等価である。
高周波に対して任意の位相遅延を与える回路として直交変調器（例えば製品名：Hittite HMC525LC4）がある。図１に含まれている直交変調器（同相信号及び直交信号成分を入力し、直交変調された送信信号を出力する機器）200では、基準クロック100からのクロック信号に対し分配器201を用いて同相の信号210と90度の位相差を持つ信号211を作る。同相信号210は乗算器202により、D/A変換器Ｉ（デジタル信号をアナログ信号に変換する装置）205の出力212と掛け合わされる。同様に90度ずれた信号211は乗算器203によりD/A変換器Ｑ206の出力213と掛け合わされる。こうして得られた２つの乗算信号は合成器204によって足しあわされる。信号212の電圧がcos(θ)に比例した電圧、信号213の電圧がsin(θ)に比例した電圧である条件においては、この足しあわされた信号216は、元の基準クロック100の出力とはθだけずれた位相で基準クロックと同じ周波数で振動する信号となる。この信号２１６を、Ｍ回(Ｍは整数)カウントするごとにパルスを出力するカウンタ400に入力すると、カウンタからは基準クロックをＭで分周したパルス信号410（レーザークロック用）が出力される。Ｍで分周とは、Ｍを整数としてカウンタでM回クロックを計数するたびにパルス出力を出すことである。 After all, this delayed signal is the phase

Is equivalent to a delayed signal.
There is a quadrature modulator (for example, product name: Hittite HMC525LC4) as a circuit that gives an arbitrary phase delay to a high frequency. In the quadrature modulator 200 (apparatus that inputs in-phase signals and quadrature signal components and outputs a quadrature-modulated transmission signal) 200 included in FIG. 1, a distributor 201 is used for the clock signal from the reference clock 100. Thus, a signal 211 having a phase difference of 90 degrees with the in-phase signal 210 is generated. In-phase signal 210 is multiplied by multiplier 202 with output 212 of D / A converter I (device for converting a digital signal into an analog signal) 205. Similarly, the signal 211 shifted by 90 degrees is multiplied by the output 203 of the D / A converter Q206 by the multiplier 203. The two multiplication signals thus obtained are added together by the synthesizer 204. Under the condition that the voltage of the signal 212 is a voltage proportional to cos (θ) and the voltage of the signal 213 is a voltage proportional to sin (θ), the added signal 216 is equal to the output of the original reference clock 100. Becomes a signal oscillating at the same frequency as the reference clock with a phase shifted by θ. When this signal 216 is input to a counter 400 that outputs a pulse every M times (M is an integer), a pulse signal 410 (for a laser clock) obtained by dividing the reference clock by M is output from the counter. Dividing by M is outputting a pulse every time M is counted by a counter with M as an integer.

  On the other hand, the emitted light is simulated by a signal 501 obtained by directly dividing the clock signal from the reference clock by M by the counter 500. The time difference between the signal 410 and the signal 501 is a value obtained by multiplying θ divided by 2π and the clock cycle. Normally, the set phase range uses a value between 0 and 360 degrees, but when the frequency division ratio M of the counter is larger than 1, the value from 0 to 360 M degrees is meaningful, and the pulse signal 410 As for the time difference between the two signals 501, the delay time can be continuously changed in the range from 0 to M times the period of the reference clock by changing θ in the range from 0 to 360 M degrees.

  In the present invention, the clock signal that has passed through the quadrature modulator is counted by a counter to obtain a delayed signal. The phase of the quadrature modulator is changed by a value obtained by dividing the delay time change amount by the period of the clock signal and multiplying by 2p. Since the quadrature modulator can generate an arbitrary phase including an integer rotation of the clock, the delay amount can be set in units finer than the cycle of the clock signal. Further, since the phase stability is constant regardless of the phase rotation speed, the accuracy does not deteriorate even for a large time delay. This circuit can be constructed only of a compact integrated circuit and takes up little space. In addition, there is no concern that the optical axis of the laser changes as in the case of optical delay, and light from a plurality of ultrashort pulse lasers or a light source driven at a high frequency can be irradiated onto a sample or product in a time-controlled manner.

  The present invention pays attention to the fact that the quadrature modulator can change the phase of the reference clock signal infinitely, and is that the delay time is linked to the phase change. This method is characterized in that there is no deterioration in accuracy with respect to an increase in delay amount, and that the delay time can be easily input and confirmed by a display.

  The basic configuration of the present invention includes a phase delay of a high frequency by a quadrature modulator and a counter for counting the high frequency. FIG. 1 shows an example of the configuration. An output of the reference clock 100 is input to the quadrature modulator 200, and a phase-modulated clock signal 216 is output. The phase-modulated clock signal is counted by the counter 400, and a pulse signal 410 is output every time the set frequency dividing ratio is counted M times. The delay amount of the output pulse signal 410 with respect to the radiation light signal 501 can be adjusted by changing the phase change amount given by the quadrature modulator 200. The phase change speed is not necessarily synchronized with the frequency of the frequency-divided signal, and may be changed slowly. This means that a D / A converter having a high resolution can be used, and improvement in phase setting accuracy is expected.

  In the present invention, a quadrature modulator including a distributor, a multiplier, a D / A converter and a combiner is used, and a signal from a reference clock is converted into a signal having the same phase and a phase difference by the distributor. Then, the signal of the same phase is multiplied by the output of the D / A converter in one multiplier to obtain one multiplication signal, and the signal having the phase difference is output from the other D / A converter in the other multiplier. To obtain the other multiplication signal, and add the two obtained multiplication signals in the synthesizer to obtain a vibration signal having the same frequency as the reference clock having a phase delayed from the reference clock signal. By using the delayed signal, the control signal input to the D / A converter of the quadrature modulator through the controller is continuously changed, and any continuous signal exceeding the period of the reference clock or within the range thereof can be obtained. Delay amount trigger signal The issue is being done.

(1) Delay in synchronization between reference clock and pulse laser Example of giving a delay time of 3.5 nanoseconds when the frequency of the reference clock signal of the synchrotron radiation source is 500 MHz and the laser trigger frequency division ratio M is 3 Consider.

  Fig. 1 shows a conceptual diagram of a high-frequency clock trigger continuous delay device. The output of the signal of the reference high frequency clock 100 is branched by the distributor 201 into two signals, a signal 211 in phase with the reference clock and a signal 211 shifted by 90 degrees. A multiplier I202 is connected to the in-phase signal, and a multiplier Q-203 is connected to the signal shifted by 90 degrees. The D / A converter I-205 connected to the multiplier I is normally 1V output, and the output of the D / A converter Q-206 connected to the multiplier Q-203 is normally 0V output. The outputs of the two multipliers are added together with the same phase using a combiner I-204. After the added signal 216 is branched by the distributor 207, one is input as a clock signal to the counter I-400, and the other is output as a laser clock signal 411 after passing through the band pass filter 401. The The counter 1 outputs a laser trigger 410 every time the clock is counted M times. On the other hand, the radiated light signal 501 can be simulated by the output of the counter 2-500 that divides the reference clock by M.

  The delay time between the radiation light and the laser pulse is required to be set continuously with an accuracy of several picoseconds within a range of several tens of nanoseconds. When changing the delay amount, first, a set value of the delay amount is given to the controller 300 from the outside. The controller calculates the amount of phase change to be applied to the quadrature modulator from the set delay amount, and sequentially sets the outputs for the D / A converter I and the D / A converter Q.

For example, a case where the delay amount is 3.5 nanoseconds will be described. This is an operation of delaying the laser clock relative to the synchrotron radiation synchronized with the reference clock by 3.5 nanoseconds. Considering the amount of delay in terms of phase, since the period of the reference high-frequency clock is 2 nanoseconds, the delay created by the quadrature modulator is 3.5 nanoseconds / 2.0 nanoseconds × 360 degrees = 630 degrees in terms of phase. Therefore, it is only necessary to change the phase of the clock to the laser by 630 degrees with respect to the reference high frequency clock. Some phase shifters use PIN diodes, but these phase shifters have a limited variable range. If the variable range is wide, it is difficult to obtain high stability and setting accuracy. Here, in order to realize this, a phase shifter using a quadrature modulator is employed. To obtain a phase shift of 630 degrees, the control voltage 212 to the D / A converter I is 1.0V to 0.0V, -1.0V, 0.0V, + 1.0V, 0.0V,- The voltage is changed to 0.0V in the order of 1.0V, and the control voltage 213 of D / A converter Q is synchronized with the control voltage of D / A converter I from 0.0V to 1.0V, 0.0V, -1.0V, What is necessary is just to change to -1.0V in order of 0.0V, 1.0V, 0.0V. Since the laser trigger signal after changing the D / A converter output is output according to the phase-modulated clock, the laser clock signal and the trigger signal always have a set delay amount.
FIG. 2 shows a signal 210 having the same phase as the signal from the reference clock, a signal 211 having a phase difference of 90 degrees, a control output 212 from the converter I, a control output 213 from the converter G, a signal 212 and a signal 213. , The M-divided pulse signal 410 from the counter 400, and the M-divided synchrotron radiation timing signal 501 from the counter 500 are shown. At the point a, the synchrotron radiation signal 501 and the output signal 410 have the same timing, but at the point c, the timing of 410 is output with a delay of 3.5 nanoseconds compared to the timing 501.

(2) About the delay in the trigger used in the accelerator The pulse delay device synchronized with the reference clock with high accuracy by resetting the counter of the device described in (1) above with an external trigger and outputting only one pulse. realizable. FIG. 3 shows a conceptual diagram of an apparatus for giving a delay. In the delay device of FIG. 3, the output of the signal of the reference high-frequency clock 100 is branched by the distributor 201 into two signals 211, which are 90 degrees apart from the signal 210 in phase with the reference clock. A multiplier I-202 is connected to the in-phase signal, and a multiplier Q-203 is connected to the signal shifted by 90 degrees. The output 205 of the D / A converter I connected to the multiplier I is normally 1 output, and the output −206 of the D / A converter Q connected to the multiplier Q is normally 0 output. The outputs of the two multipliers are added together with the same phase using the combiner 204. The added signal is input to the counter 1-400. A delay longer than the reference clock period with respect to the start trigger 601 is set as an integer value in the counter 400, and a delay within the reference clock period is changed using a quadrature modulator to change the phase shift of the clock of the counter 400. Let As an example, the case of trigger delay of 18 ns and 21.5 ns using a 500 MHz reference clock is shown. When delaying 18 nanoseconds, 18 nanoseconds is 18/2 = 9.0, or exactly 9 times the clock period of 2 nanoseconds. 9 is set as a set value (603 in FIG. 3) from the controller to the counter. When receiving the start signal, the controller sets a phase rotation angle of 0 degree for the quadrature modulator. In this case, 212 remains at 1.0V and 213 remains at 0.0V. When a start signal is input at the timing a in FIG. 2, the counter starts counting and outputs a delay trigger at the timing b. After outputting the signal b, the counter stops operating until the next start signal is received. Next, a case where a delay of 21.5 nanoseconds is performed is shown. 21.5 nanoseconds will be delayed by 3.5 nanoseconds compared to 18 nanoseconds. Accordingly, when the set value of the counter is kept at 9, the phase is rotated by 630 degrees using the quadrature modulator. When the start signal is input, the counter starts counting. At the same time, the controller changes the control voltage to the quadrature modulator as shown in FIG. The counter outputs a delay trigger c when the waveform is counted nine times and stops operating until the next start signal is input. The delay trigger c is 21.5 nanoseconds with respect to the start signal a. After outputting the delay trigger, the controller restores the control voltage to the quadrature modulator to a normal value (212 is 1.0 V, 213 is 0.0 V), and prepares for the next start signal.
In the above method, when the delay time is short, it is necessary to change the control signal in a short time after receiving the start signal. In order to avoid this, there is a method of applying a DC control voltage to the quadrature modulator so as to steadily give a phase change corresponding to a fraction of the period. However, in this case, when the clock counting by the counter is performed at the timing of rising across the clock zero voltage, the reset signal 602 and the timing of the zero crossing are shot-by-shot when the set delay amount is close to half of the clock cycle. There is a possibility of going around. This indicates the possibility of jitter in the clock period. In order to avoid this, a programmable delay device 600 is added to the reset signal 602 in the vicinity where the set delay amount satisfies the above condition to give a delay of half the clock period, and the set value of the counter is decreased by 1. Can be avoided.

  In recent years, there has been a demand in the field of experiments using lasers to generate a clock signal and a trigger signal that are synchronized with a reference clock with high accuracy. High-speed spectroscopy using an ultrashort pulse laser has been conventionally performed by using a single laser light source and branching it. Several years ago, since a method of controlling ultra-short pulse laser light using an external trigger was developed, it became possible to use multiple ultra-short pulse laser light sources. A device that accurately sweeps the time delay over a wide range is required. Although the sweep range is actually narrow, pump and probe experiments using ultra-short pulse lasers have already been conducted in Japan and other countries at synchrotron radiation facilities, and equipment that sweeps the high-frequency time delay of such ultra-short pulse lasers There seems to be a need. In addition, many nonlinear spectroscopy using multiple ultrashort pulse lasers and pump / probe measurements are performed in research facilities such as universities and research institutes. The market for such sweeping equipment is limited to synchrotron radiation facilities. It extends to R & D facilities in general.

  In addition, various pulse electromagnets, pulse RF generators, and the like are used for the accelerator, and their trigger timing is required to have high synchronization with the RF reference signal. The sweeping instrument of the present invention may meet and satisfy these requirements.

  That is, the present invention includes pump / probe experiments using synchrotron radiation and ultrashort pulse laser, irradiation timing control of multiple ultrashort pulse lasers, accelerator pulse magnet power trigger, pulse RF power trigger, monitor trigger, etc. Available in the field of development.

It is a figure which shows the high frequency clock trigger continuous delay apparatus in this invention. It is a figure which shows the time relationship of the reference clock in this invention, a D / A converter control voltage, a trigger output, and a radiated light timing. It is a figure which shows the delay in the trigger used with the accelerator in this invention.

Claims (2)

In a method for generating a pulse signal and a delay clock signal of an arbitrary delay time with high accuracy with respect to a pulse signal synchronized with a reference clock using a controller and a counter combined with a quadrature modulator (a circuit that provides an arbitrary phase delay), By continuously changing the control signal input from the controller to the quadrature modulator and moving the phase at the same frequency, an arbitrary continuous delay amount within or exceeding the period of the reference clock can be set. Performing said method. In the method of delaying the start signal continuously and arbitrarily with high precision using a counter combined with a quadrature modulator, a signal that is phase-modulated using a quadrature modulator is used as the input clock signal to the counter, and the same frequency is used . The method of realizing a pulse delay circuit having a delay time setting resolution equal to or less than the reference clock period with high accuracy by moving the phase with the .

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