JPH10282240A - Waveform shaping circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent fluctuation from occurring in crest and a baseline even when noise is superimposed on step form waves by providing a differential amplifier which receives the input of a signal delayed by holding a crest value just before the change of crest by a sample hold circuit and of a signal after the change of crest. SOLUTION: When the occurrence of radiation is detected at an event circuit, a sample hold circuit 5 is set to a hold mode during the period of the generation of pulses from a point of approximately 1/2 of the amount of delay of a delay line 1, and a level just before the change of step form waves is held in a capacitor CH. As a result of this, a pulse that a signal of the output end B of a differential amplifier 2 is deducted from a signal of the output end D of the sample hold circuit 5 occurs in the output end E of a differential amplifier 7. A smoothing circuit 3 smooths a step form output signal from a preamplifier with a low S/N ratio to remove noise and obtains the center of the crest. By this, the sample hold circuit 5 can hold the center of the crest and eliminate the fluctuation of output which occurs due to noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform shaping method for shaping an input signal into a pulse signal having a predetermined time width in measuring radiation or the like.

[0002]

2. Description of the Related Art As shown in FIG. 5, in a high-resolution radiation measuring apparatus using a silicon or germanium semiconductor detector 21, a preamplifier 22 for outputting a step wave having a height proportional to the energy of photons is provided. used. The outline of the preamplifier 22 is an integrator in which a capacitor is connected between the input and output of the operational amplifier as shown in the figure. Each time radiation is detected, the capacitor accumulates an electric charge, so that the output becomes a step wave. This staircase output is reset by short-circuiting the capacitor with a switch for a short period of time before the circuit saturates to discharge the charge. The optical feedback type preamplifier shown in FIG. 5 is reset by comparing the integrator output with the reference voltage, and outputting a signal when the integrator output exceeds the reference voltage.
Is turned on to irradiate the exposed FET gate on the integrator input side to short-circuit the gate and source.

The staircase wave output of the preamplifier 22 is measured by the main amplifier 23 shown in FIG. 6 after being converted into an isolated pulse proportional to the wave height of each staircase wave. The conversion into isolated pulses in the main amplifier is called waveform shaping,
As shown in FIG. 7, various shapes such as Gaussian wave shaping (FIG. 7A), triangular wave shaping (FIG. 7B), and trapezoidal wave shaping (FIG. 7C) are performed.

As shown in FIG. 8, a general waveform shaping circuit includes a differentiating circuit 24 and several stages of low-pass filter circuits (three stages of low-pass filter circuits 25 to 27 in the illustrated example). You. As shown in FIG. 8, a desired shaped wave can be obtained by appropriately adding the outputs of the respective filter stages by the adder 28 except for the Gaussian wave.

As a main amplifier of a preamplifier for outputting a staircase wave, there is a method of generating a pulse signal using delay clipping (Japanese Patent Publication No. 4-79555). This method is shown in the block diagram of FIG. This will be schematically described with reference to the waveform diagram of FIG. A staircase wave (a) from a preamplifier (not shown) is applied to one input terminal of a differential amplifier 32. On the other hand, the output of the differential amplifier 32 is
The detection signal (b) is delayed by the single shot pulse width of the single shot circuits 34 and 35 to generate a pulse signal (d). The operational amplifier 30 to which the staircase wave (a) is input is connected to the operational amplifier 31 via the switch 38, and these constitute a sample and hold circuit. The output of the sample and hold circuit is applied to the other input terminal of the differential amplifier 32. Then, the switch 38 is set to the delay pulse signal (d).
And the sample height of the staircase wave is sampled and held, and the delayed staircase wave (e) is applied to the other input terminal of the differential amplifier 32. When the staircase wave (a) and the delayed staircase wave (e) A difference signal (f) is obtained, which is an isolated pulse proportional to the height of the individual step wave.

[0006]

The method shown in FIG. 9 is as follows.
A pulse signal corresponding to the height of the staircase wave can be generated only when the wave height of each stage of the staircase wave is stable and there is no noise. However, the sample
When holding the input signal, the hold circuit holds the input signal level at the moment when the hold mode is set. Therefore, when noise is superimposed on the input signal (staircase wave) as shown in FIG. , The output (e) of the sample and hold circuit fluctuates by the width of the maximum noise,
The pulse height of the pulse signal (f) generated by taking the difference between the original signal and the delayed signal in the differential amplifier circuit 32, and the base line also similarly fluctuates by the width of the noise. . In Japanese Patent Publication No. 4-79555, a baseline correction voltage is generated by an operation error detection circuit 36 and applied to the base side of the charge capacitor 37. However, the operation error detection circuit 36 here uses a general baseline. It is considered as a stabilization circuit, and only corrects a DC error. Even if a base correction is performed, fluctuations due to noise cannot be eliminated only by changing the DC level.

The pulse signal generated by the waveform shaping method described in Japanese Patent Publication No. 4-79555 has a different wave height for each shaping due to superimposed noise even for the same radiation signal. It is possible.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a waveform shaping circuit that does not cause fluctuations in both the wave height and the baseline even when noise is superimposed on the staircase wave. I do.

[0009]

According to the present invention, there is provided a sample and hold circuit to which a signal whose wave height changes stepwise is input, and a sample and hold circuit for holding and delaying the wave height immediately before the wave height changes. And a differential amplifier circuit to which the signal after the change in the wave height is inputted, wherein a smoothing circuit is provided on the input side of the sample-and-hold circuit. Further, the present invention is characterized in that an integrating circuit is connected to the output side of the differential amplifier circuit. Further, the present invention is characterized in that a means for switching a smoothing time constant is provided in the smoothing circuit.

[0010]

Embodiments of the present invention will be described below. FIG. 1 is a diagram showing an example of an embodiment of the present invention, and FIG. 2 is a diagram showing a timing waveform of FIG. In the figure, 1 is a delay line, 2 is an operational amplifier, 3 is a smoothing circuit, 4 and 6 are semiconductor switches, 5 is a sample and hold circuit, and 7 is a differential amplifier. In the figure, a staircase wave signal from a preamplifier (not shown) that outputs a staircase wave is input to (A),
In FIG. 2B, a staircase wave signal delayed by the delay amount of the delay line 1 is generated (FIGS. 2A and 2B). When no radiation is detected by an event detection circuit (not shown), the sample and hold circuit 5 is in the sample mode and SW1
Is open and SW2 is closed. At this time, since the same signal is generated at (B) (the output terminal of the operational amplifier 2) and (D) (the output terminal of the sample-and-hold circuit 5), the differential amplifier 7
At the output terminal (E) of the differential amplifier 7
The (D) signal from which noise has been removed through the smoothing circuit 3 is input to the + terminal side of the differential amplifier 7.
Since a signal including noise at the output terminal (B) of the operational amplifier 2 is input, the noise is output without being canceled out (FIG. 2E).

When the occurrence of radiation is detected by the event detection circuit, the sample-and-hold circuit 5 is set to the hold mode during a period of pulse generation from a point of about 1/2 of the delay amount of the delay line 1. The SW2 had the closed far from this point in the open, the level immediately before the staircase is changed is held in the capacitor C _H. As a result, a pulse signal is generated at the output terminal (E) of the differential amplifier 7 by subtracting the signal at the output terminal (B) of the differential amplifier 2 from the signal at the output terminal (D) of the sample and hold circuit. What.

The smoothing circuit 3 smoothes the staircase output signal from the preamplifier having a poor S / N ratio to remove noise and obtain the center of the wave height. As a result, the sample and hold circuit 5 holds the center of the wave height, and can eliminate output fluctuations caused by noise.

The semiconductor switch 4 (SW1) includes a smoothing circuit 3
Is to shorten the settling time. That is,
When the crest of the staircase wave in (B) changes, the signal at the output terminal (C) of the smoothing circuit 3 (FIG. 2 (C)) changes exponentially and indirectly in proportion to the smoothing time constant, so that a stable crest value is obtained. , It takes a long time, and the molding interval is limited by the smoothing time constant. However, immediately after the sample-and-hold circuit 5 enters the hold mode (SW2 open), SW1 is immediately closed to short-circuit the smoothing resistor R _S , and if the smoothing time constant is made extremely small, the output of the smoothing circuit 3 becomes the input signal. Since the level is quickly followed, the molding interval is no longer limited by the smoothing time constant. In this case, SW1
If the short-circuit time is long, the smoothing is affected, so the short-circuit time should be as short as possible.

As described above, during a period in which no pulse signal is generated, SW1 is opened and the sample and hold circuit is closed with SW2 closed so that the signal at the output terminal (E) of the differential amplifier 7 is at zero level. The mode is set so that each input terminal of the differential amplifier 7 has the same baseline.

Next, another embodiment of the present invention will be described. FIG. 3 is a diagram showing a shaping circuit in which an integrating circuit is further connected to FIG. 1, and FIG. 4 is a timing waveform diagram. The same reference numerals as those in FIG. 1 indicate the same contents. 8 is a gated integrator, 9 and 11 are semiconductor switches,
Reference numeral 10 denotes an operational amplifier.

The gated integrator 8 receives the output of the differential amplifier 7 via the semiconductor switch 9 (SW3), integrates the input signal with an integrator having a capacitor connected between the input and output of the operational amplifier 10, and measures the wave height. After that, the semiconductor switch 11 (SW4) is short-circuited and reset to remove the influence of noise superimposed on the peak value.

When no radiation is detected by the event detection circuit, the sample and hold circuit 5 is in the sample mode, and the switch 4 (SW1) and the switch 9
(SW3), switch 11 (SW4) is open, switch 6
(SW2) is in a closed state. At this time, (B) (the output terminal of the operational amplifier 2) and (D) (the sample-and-hold circuit 5)
Since the same signal is generated at the output terminal (E), the output terminal (E) of the differential amplifier 7 has a zero level, but the + terminal side of the differential amplifier 7 has passed through the smoothing circuit 3 to remove noise. The signal (D) is input, and the negative terminal of the differential amplifier 7 is
Since a signal including noise at the output terminal (B) of the operational amplifier 2 is input, the noise is output without being cancelled, as in the case of FIG.

When the occurrence of radiation is detected by the event detection circuit, the sample-and-hold circuit 5 is set to the hold mode for a period of pulse generation from a point of about 1/2 of the delay amount of the delay line. so the SW2 which has been closed and opened up, the level immediately before the staircase is changed is held in the capacitor C _H.

As a result, the differential amplifier 7 output (E) generates a pulse signal in which the signal at the output terminal (B) of the operational amplifier 2 is subtracted from the signal at the output terminal (D) of the sample and hold circuit. .

After the pulse signal is stabilized, the switch 9 (S
When W3) is closed, the gated integrator starts to integrate the pulse signal. Thereby, (F) rises linearly with time. When the integration of the specific period of the pulse signal is completed, the switch 9 (SW3) is opened,
The integration result is held in Ci. This hold value is A
After being measured by a D converter (not shown), the switch 11
It is reset by closing (SW4).

When a pulse signal formed by a circuit as in the embodiment shown in FIG. 1 is directly measured by a general radiation AD converter, the noise peak that occurs first is represented by A.
Due to the D conversion, an error corresponding to the noise amplitude at the maximum occurs. However, if the integration is performed, noise centered on the peak value is canceled, and no error due to the noise occurs.

During a period in which no pulse signal is generated, the output (E) of the differential amplifier 7 is set to a zero level so that
1 is open, the sample and hold amplifier is closed and SW2 is set to the sample mode. Further, the gated integrator output (F) is set to zero level except for the integration and the period during which the integration result is held.
W3 is open and W4 is closed.

[0023]

As described above, according to the present invention, a smoothing circuit is provided at the input of the sample-and-hold circuit to smooth the signal to remove superimposed noise and to hold the center of the wave height. By doing so, it is possible to prevent fluctuations in the pulse wave height, and it is possible to reduce the settling time by making it possible to change the smoothing time constant of the smoothing circuit. In addition, by connecting an integrating circuit to the waveform shaping circuit and integrating the shaped signal, it is possible to cancel the influence of noise superimposed on the wave height of the shaped pulse signal.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a waveform shaping circuit according to the present invention.

FIG. 2 is a waveform chart of the waveform shaping circuit of FIG. 1;

FIG. 3 is a diagram showing another example of the waveform shaping circuit of the present invention.

FIG. 4 is a waveform chart of the waveform shaping circuit of FIG. 3;

FIG. 5 is a diagram illustrating a preamplifier.

FIG. 6 is a diagram illustrating a main amplifier.

FIG. 7 is a diagram illustrating an example of an output waveform of a main amplifier.

FIG. 8 is a diagram showing a waveform shaping circuit.

FIG. 9 is a diagram illustrating a method of generating a pulse signal using delay clipping.

FIG. 10 is a timing waveform diagram.

FIG. 11 is a diagram illustrating a pulse waveform when noise is superimposed on the height of the staircase wave.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Delay line, 2 ... Op amp, 3 ... Smoothing circuit, 4 ... Smoothing time constant switch, 5 ... Sample and hold circuit, 6 ... Switch, 7 ... Differential amplifier, 8 ... Gated
Integrator, 9 ... switch, 10 ... operational amplifier.

Claims (3)

[Claims] 1. A sample and hold circuit to which a signal whose wave height changes stepwise is input, a signal whose sample height is held and delayed by the sample and hold circuit and a wave height changes. What is claimed is: 1. A waveform shaping circuit comprising: a differential amplifier circuit to which a subsequent signal is input; and a smoothing circuit provided on an input side of a sample and hold circuit. 2. The waveform shaping circuit according to claim 1, wherein
A waveform shaping circuit, wherein an integrating circuit is connected to an output side of the differential amplifier circuit. 3. The waveform shaping circuit according to claim 1, wherein a means for switching a smoothing time constant is provided in the smoothing circuit.