JPS6035811A - Preamplifier for semiconductor radiation measurement equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (2) Industrial field of application The present invention relates to a semiconductor radiation measurement device used in medical and nuclear radiation measurement and diagnostic equipment that requires measurement of dose rates over a wide range of areas. This is related to the prefix increase 1 instrument.

2. Description of the Related Art Structures of Conventional Examples and Their Problems In recent years, semiconductor radiation measuring devices have been widely used in the fields of medical and nuclear radiation measurement.

At nuclear power plants, etc., in order to protect the safety of on-site workers,
Radiation measurement devices that detect radiation abnormalities are essential and generally required to be carried. Radiation measurement in this field generally involves counting the number of radiations within a certain period of time in order to determine whether the number of radiations is larger than normal. Such a radiation measurement device needs to be small and lightweight so that it is convenient to carry, and at the same time, it needs to be fast enough to measure even weak radiation and count radiation at large dose rates.

Semiconductor detectors for detecting radiation are small, highly sensitive, and capable of high-speed measurement depending on the method of application, and have superior characteristics than (3) Geiger-Mueller tube (CGM tube) type detectors. However, the output signal of a semiconductor detector is weak, and a preamplifier is essential for actual signal processing and counting. The preamplifier is required to have performance that does not diminish the advantages of the semiconductor detector. Particularly, in the above-mentioned applications, issues arise in terms of S/N and the high speed with which individual radiation can be separated and counted at high dose rates. Recently, nuclear power generation.

As the use of nuclear power increases, there is a strong demand for a preamplifier for semiconductor radiation measuring devices that meets these requirements.

FIG. 1 shows a configuration diagram of a radiation measuring device that counts the number of radiation quanta and measures the radiation dose. (1) is a semiconductor detector,
(2) is a bias resistor that supplies bias resistor VD to the semiconductor detector (υ), (3) is a preamplifier, (4) is a comparator circuit, and (5) is an input during a period specified by a timer circuit (6). A counter circuit that counts the number of radiation emitted (7
) is a display circuit that displays the contents of the counter circuit (5) and notifies the radiation dose.

The operation will be explained below. The preamplifier (3) is (4
) Semiconductor detection +a (1) converts the charge generated by the incident radiation into a voltage and outputs it. Comparator circuit (4)
By having an appropriate threshold voltage, the preamplifier (3) removes noise from the output signal and converts signals above the threshold voltage to a level that can be input to the counter circuit (5) as a signal. Figure 2 (al (bl) shows the signal waveforms at point a of the preamplifier output and point b of the comparator circuit output shown in Figure 1. Therefore, the output of the comparator circuit (5) is the signal waveform of the semiconductor detector (υ The number of pulse trains is the same as the number of radiation quantum incident on the pulse train.The pulse train is counted by a counter circuit (5).The counting period is defined by a timer circuit (6).The count result is displayed by a display circuit (7). The measurement result is displayed on the screen so that the user of the measuring device can easily know the measurement result.In the semiconductor type radiation measuring device having such a configuration, the preamplifier (3) is required to have the following requirements.

(1) Low noise (2) High First, suppose that the S/IJ of the preamplifier (3) is poor and the output signal waveform of the preamplifier (3) is as shown in FIG. 2 (at).

At this time (5), if the threshold voltage is vT in Figure 2 (al), then (b
As shown in 5, noise is also output as a pulse as a signal,
The counter circuit (5) counts incorrectly. In order to prevent this, increasing the threshold voltage to vT' eliminates the occurrence of malfunctions due to noise, but relatively low level signals are regarded as noise and pulses are no longer output. Since the radiation measuring device configured as described above counts inputs and numbers within a certain period, the above-mentioned counting errors are not allowed and pose a serious problem in terms of radiation safety management. Therefore,
The preamplifier (3) is required to have low noise.

In addition, the response speed of preamplification vr (3) is slow, as shown in Figure 2 (
Suppose that the signal that is supposed to be output in the form shown by a'1 becomes (Kl).If the response speed is slow, if the inputs are input continuously, the separation of individual signals will be poor, and the comparator circuit output When a preamplifier with high response speed is used, (G1 becomes (G1), and what should originally be output as multiple pulse trains is output as one pulse. As shown in the figure (fl), increasing the threshold voltage vT to vT' (6) increases the resolution of individual signals, but the relatively low level 1Jij is regarded as noise. Furthermore, the preamplifier (3) is also required to be high speed.

FIG. 3 shows a configuration diagram of a preamplifier of a conventional semiconductor radiation measuring device, where (8) is an inverting amplifier with a gain of (-A,);
(9) is the feedback capacitor and feedback resistor connected between the output of the inverting amplifier (8). aυ is a differentiating circuit, and (2) is a buffer amplifier with gain [A2]. FIG. 4 is a diagram showing signal waveforms at the output point C of the inverting amplifier (8) and the output point A of the preamplifier.

The inverting amplifier (8) constitutes a mirror integrator with a feedback capacitor (9) and a feedback resistor Go, and converts charges caused by radiation generated by the semiconductor detector (1) into voltage. I will discuss this point in a little more detail. Figure 5 shows a semiconductor detector (
This is a diagram for explaining using the equivalent circuit of 1), and shows the circuit up to the front of the differential circuit circle.

α is the current source representing the current generated by the incident radiation and flowing out of the detector (1), and α is the equivalent output capacitance of the detector (1).

(7) The output voltage of the inverting amplifier (3) is expressed as follows using Laplace transform. Now, the gain of the inverting amplifier (3) is determined so as to satisfy the following. On the other hand, the outflow current of semiconductor detection ′u(υ is 1=Io
It can be approximated as e-“1.Ie-“t-0,” that is, the time from when it flows out to zero is called the collection time, and the number Ion
It can be seen that the semiconductor detector (υ) is quite fast. Therefore, the output voltage is (8). Now, the feedback capacitor C7 is set so that α>>i=β f is satisfied. If the feedback resistor R1 is selected as In reality, the charge charged in the feedback capacitor cf is slowly discharged through the feedback resistor R.

Now, the signal obtained in this way is as shown in Figure 4 (shown as cl) if the radiation input is at an interval that is tighter than the time constant determined by the feedback capacitance C, ((1) and the feedback resistance R, Q (l) mentioned above. (
9) It becomes like a step. The stepped waveform is permissible at the first stage where the signal level is low, but when it goes to the subsequent stage where the signal is amplified, it requires an excessive dynamic range.

Further, in the radiation measuring device for counting the number of radiations shown in FIG. 1, it becomes impossible to set the Ll value voltage of the comparator circuit (4), and normal operation cannot be expected. Therefore, the output signal of the inverting amplifier (3) is differentiated by a differentiating circuit aη and converted into a pulse having a certain differentiation time constant τ. The buffer amplifier (6) is for eliminating the influence of the subsequent stage. Therefore, the output signal as a preamplifier is
It becomes as shown in FIG. 4 (at) and is sent to the comparator circuit (4), making it possible to count the number of radiation.

However, the above configuration has the following problems. Traditional preamplifiers use semiconductor detectors (
Since the output current in step 1) is integrated and converted to voltage, if the output current has a narrow pulse width as shown in Figure 6 (4),
As shown in FIG. 6(b), the signal amplitude after conversion to voltage becomes small, and as shown in FIG. 6(c), the amplitude after differentiation also becomes small. (10) Therefore, when using a high-speed semiconductor detector with a short collection time, a sufficient output voltage cannot be obtained for the preamplification kg, and as the amplitude of the output current becomes smaller, the noise level remains the same. Also, the K S/N deteriorates relatively rapidly. This can be easily understood from equation (2).

Furthermore, the integral output of the inverting amplifier (3) must be differentiated by the differential 4*aη, but the differential time constant at this time poses a problem. Essentially, it is desirable that the differential time constant be equal to or shorter than the time constant 1 of the semiconductor detector (1). This is because it is most desirable that the limit of the input interval at which individual radiations can be separated is determined by the collection time of the semiconductor detector (1). That is,
As shown in Figure 7 (a), although the output waveform of the semiconductor detector separates the individual radiation inputs, the output waveform of the differential circuit after passing through the integrator as shown in Figure 7 (ol) If the time constant is large, the ability to resolve individual signals with respect to radiation input will decrease, causing counting errors as shown in Figure 7 (c).Also, differentiating circuits generally tend to amplify noise;
Differential time constant (11) This becomes more noticeable as the number becomes shorter. Therefore, in a preamplifier that is required to have low noise, there is naturally a limit of one circuit, which is about several tens of microseconds without any circuit processing, and about several microseconds even if complicated means are used. Therefore, as a radiation measuring device, the speed is more than an order of magnitude slower than the capability of semiconductor detection IrM.

As described above, the conventional preamplifier for a semiconductor type radiation measuring device does not take full advantage of the capabilities of a semiconductor detector in terms of both S and speed.

Purpose of the Invention The present invention solves the above-mentioned conventional problems.It is an object of the present invention to provide a preamplifier for a semiconductor radiation measurement device that maximizes the capabilities of a radiation semiconductor detector and has low noise and high speed. This is the purpose.

Structure of the Invention The present invention is a low input impedance preamplifier configured by a high gain amplifier and a feedback means connected between the output terminal of the amplifier, and maximizes the ability of a semiconductor (12) detector. This technology is utilized to realize low noise and high speed.

Description of examples Embodiments of the present invention will be described below based on the drawings.

FIG. 8 shows a configuration diagram of a preamplifier for a semiconductor type radiation measuring device according to a first embodiment of the present invention. The cry is the gain (-A
The inverting amplifier 3), 0→, is a feedback resistor R,/ as a feedback means connected to the input and output of the inverting amplifier (to).

The operation of the preamplifier of the first embodiment configured in this manner will be described below. FIG. 9 shows an equivalent circuit of the semiconductor detector (1) in order to explain the operation of the first embodiment. In FIG. 9, the input impedance Zin when looking at the preamplifier from the A-A side is as follows. Isometrically, the load on the semiconductor detector (1) is Zin. FIG. 10 illustrates this.

Now, when the input signal frequency of the preamplifier is f (13), the input impedance Zin is Z in <<-'-1 ... Song... (3) 2πf
When C6 is satisfied, the output current of the semiconductor detector (1) is input to the preamplifier without flowing to the equivalent output capacitance C3 (1).The current input to the preamplifier is input to the inverting amplifier WQfil. If the input impedance is sufficiently high, for example if the first stage of an inverting amplifier is a FET input, the return M resistance R,
/αQ, and the voltage drop becomes the output voltage of the preamplifier. In this way, the preamplifier αG of the first embodiment changes the output current of the semiconductor detector (1) to -l as in the conventional example.
Instead of integrating the charge and converting it to voltage, the current is directly converted to voltage. Therefore, it is possible to configure a preamplifier that solves the problems of the conventional example at once and makes maximum use of the capabilities of the semiconductor detector (1).

Now, the first embodiment will be explained in more detail.

The output voltage of the preamplifier is expressed as Vo(sl=j, (vg) (14) using Lagrass transform. On the other hand, the output current of the semiconductor detector (1) is 1-
Since it can be approximated as Ielt, the output voltage is as follows. Expressing equation (4) in the time domain is as follows. Now, suppose that in the first embodiment, a preamplifier with A3 = 1000 R,' = 1 (MΩ) is used.At this time, the semiconductor detection M!(1)
As (15) Co=1 (pF) -15 (nS) Even if a high-speed one is used, the following holds true, and equation (4) can be considered in two areas. In other words, = -1゜Rf'e''t - -1R... River... (7) (16) However, in real life, the region of equation (6) is the area of the rise of the input signal. The time is extremely short and can be ignored from the change in the input signal.Therefore, the output signal of the preamplifier gg can be approximated by equation (7).Equation (7) is The output signal in (1) shows no deterioration in characteristics, indicating that current-voltage conversion was possible. Also, from equations (2) and (7), the maximum output of the conventional example and the first embodiment Let's compare the absolute values of the voltages.Now, let's compare the feedback capacitance C, (9), which is a typical value of 1 (pF:), to a semiconductor preamplifier and a conventional preamplifier. Even though, 2
An order of magnitude larger output signal can be obtained. This means that the S/N ratio has been improved by about two orders of magnitude, making it possible to measure even smaller input signals. In this way, the preamplifier of the first embodiment not only solves all the problems of the conventional technology at once, but also dramatically improves the performance of the semiconductor radiation measuring device. Here, the relationship between equations (3) and (5) will be briefly explained. Now, the output current of the semiconductor detection fl (1) is expressed by (17) Laplace transform: I=Jl; (i) I.

"s+a.The frequency characteristic is set as s=jω, which indicates the upper limit of the frequency included in the output current.
If the frequencies at the 5 (dB) point are f and x, then f - E = 2 degrees ° ° ° ° degree (8). On the other hand, equation (5) can be transformed as follows. Substituting equation (8) into the above equation yields.

The above equation is exactly the same as equation (3). That is, (3)
Equation (5) and Equation (5) are completely equivalent. Therefore, the preamplifier of the first embodiment fully satisfies the initial long-term impedance condition.

Furthermore, since the preamplifier of the first embodiment directly converts the input signal (18) from current to voltage, its output signal is
It has the same form as the output signal of the semiconductor detector (1) and is itself a pulse signal. Therefore, unlike the conventional example, there is no need for a differentiating circuit or a buffer amplifier, so it is possible to eliminate factors that degrade the SA, and it is also possible to reduce the size and weight of the circuit.

Although typical values have been described for the gain of the inverting amplifier and the feedback resistance R,'+l<9, the first embodiment is not restricted to these in any way.

As described above, according to the first embodiment, since a low input impedance type preamplifier constituted by a high gain inverting amplifier and a feedback resistor connected between the input and output of the inverting amplifier is used, semiconductor detection is possible. It is possible to realize a preamplifier for a semiconductor radiation measuring device that significantly improves the performance of the radiation measuring device without impairing the performance of the device.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 11 is a configuration diagram of a preamplifier for a semiconductor type radiation measuring device showing a second embodiment of the present invention.

In the same figure, both α7 and They are resistors Rf'' and Rv. (11 is a same wave number characteristic correction capacitor C whose one end is connected to the connection point of the feedback resistor a'ua and whose other end is grounded.

The operation of the semiconductor radiation measuring device preamplifier of the second embodiment configured as described above will be described below. The second embodiment is basically the same as the preamplifier of the first embodiment. That is, a low input impedance preamplifier is formed by the inverting amplifier (10) and feedback resistors R, l/gη, and Rv (18), and has the same performance and characteristics as the first embodiment.However, The preamplifier of the second embodiment further has a function of correcting the same wave number characteristic of the output signal using the frequency characteristic correction capacitor CvOI.In other words, the preamplifier of the second embodiment has a wider frequency characteristic than the preamplifier of the first embodiment. This allows correction by changing the amount of feedback depending on the frequency when the frequency characteristics of the output signal are insufficient due to the influence of stray capacitance, etc. Now, the input current of the preamplifier is i'( 20) Then, the output voltage is expressed by Laplace transform as follows.The frequency characteristic of the preamplifier output is set as 8-jω in equation (9).For example, if A3=1000, then (9 ) formula, the frequency characteristics of the preamplifier output are determined by the same wave number range used as the radiation measuring device d, for example 1
It can be approximated as below 0MHz. The OQ formula has the same output voltage as the first example (21
), vo=(R,"+Rv)t', which means that the output voltage monotonically increases at a frequency of 6 dB10 ct. In other words, in the second embodiment, the feedback resistor Rf"αη, Rv (to) and frequency characteristic correction capacitance C,
(1) By appropriately setting I, it is possible to correct the deterioration of the same wave number characteristic of the output signal without impairing the original performance, and to make the frequency characteristic wider. Preamplifiers have great effects on semiconductor radiation measurement devices that enable high-speed radiation measurements.
This dramatically improves its performance.

As described above, according to the second embodiment, in the low input impedance preamplifier configured by the high gain inverting amplifier and the feedback resistor, by providing the frequency characteristic correction capacitor CYQl, the frequency of the output signal (22) It is possible to correct deterioration of wave number characteristics and widen the band.

Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 12 shows a third embodiment of the present invention. It is a block diagram of an i1 device. In the same figure, one end of both (a) el) is connected, and the other end of (1) is connected to the input side of the inverting amplifier 'aQ119.
21) The other ends are feedback resistors RI'' and Rv' connected to the output side of the inverting amplifier 09. One end of @ is the feedback resistor...■
A frequency characteristic correction capacitor Cv' is connected to the connection point of η, and the other end is connected to the output side of the inverting amplifier 09.

The operation of the third embodiment configured as described above will be described below. The preamplifier of the third embodiment is basically the same as the first embodiment.

In other words, the inverting amplifier 0υ and the feedback resistors Ril and Rv'
+;21) forms a preamplifier I divider with low input impedance, and has the same performance and characteristics as the first embodiment. However, the @ amplifier of the third embodiment further corrects the frequency characteristics of the output signal l! by the frequency characteristic correction capacitor Cv' (a). ! have the ability. That is, in the preamplifier of the third embodiment, for example, when there is an unstable chain acid due to rotation of the inverting amplifier phase at a high frequency (23), and it is necessary to reduce the amplitude characteristics around that frequency, This is achieved by changing the amount of feedback depending on the frequency.

Now, if the input current of the preamplifier is i', then the output voltage is represented by Laplace substitution as Vo(sl=f(vo).(In the 1υ equation, s=jω and 1d, and its frequency characteristic At a frequency where the 0υ formula becomes, the output voltage becomes v o = (Rf" + Rv') t', as in the first embodiment, but at a frequency where (24) becomes, This means that the output voltage decreases.In other words, in the third embodiment, the feedback resistors R, l//Kan,
By appropriately setting Rv'shiυ and frequency characteristic correction capacitor Cv1@, it is possible to change the frequency characteristic of the output signal by changing the amount of feedback without impairing the original performance. Therefore,
The preamplifier of the third embodiment is particularly effective when the system has an unstable @ region due to its frequency characteristics, or when a relatively high frequency is not required due to the nature of the system.

As described above, according to the third embodiment, by providing the frequency characteristic correction capacitor Cv' (E) in the low input impedance preamplifier composed of a high gain inverting amplifier and a feedback resistor, the output signal Enables correction of frequency characteristics.

Next, a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 13 is a configuration diagram of a preamplifier for a semiconductor type radiation measuring device showing a fourth embodiment of the present invention. This fourth embodiment is a combination of the second (25) embodiment and the third embodiment, and operates as described above, but correction of the complex frequency characteristics of the output 1-signal is performed. It is what makes it possible. In the third embodiment, the feedback resistance is Rf''αη, the frequency characteristic correction capacitance Cv4, Cv', but other combinations of values are possible and can be changed depending on the content of correction.

Although the device shown in FIG. 1 has been described as an example of a radiation measuring device, the preamplifier of the present invention is not subject to any restrictions regarding the type of device, and other devices can be used with sufficient effect. can.

Further, although specific numerical values have been described in the examples, there is no restriction to these in any way.

Effects of the Invention According to the preamplifier for a semiconductor radiation measuring device of the present invention, it is possible to output high-speed pulses from a semiconductor detector, improve measurement accuracy in fields from low to high dose rates, and We were able to achieve a radiation quality measurement range by improving the S/1'J ratio of low-energy radiation. This makes it possible to measure radiation incidence during abnormal conditions (26), making a significant contribution to radiation safety. Furthermore, even in the field of medical radiation measurement, where pulse measurement has been difficult in the past, it is now possible to measure pulses using semiconductor detectors, making a significant contribution to reducing radiation exposure in the medical field.

In addition, the present invention makes it possible to miniaturize circuits and reduce power consumption, thereby realizing miniaturization and high integration of equipment, reducing costs and improving accuracy. It is possible to further enhance the effects of miniaturization and high stability due to miniaturization.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of a semiconductor radiation measuring device,
FIG. 2 is a diagram showing signal waveforms at each point of the semiconductor radiation measuring device shown in FIG. 1, FIG. 3 is a configuration diagram of a conventional preamplifier for a semiconductor radiation measuring device, and FIG. FIG. 5 is an equivalent circuit diagram to explain the operation of the conventional example, and FIGS. 6 and 7 are diagrams showing the signal waveforms at each point. Diagram showing signal waveforms, No. 8
(27) The figure is a configuration diagram of a preamplifier for a semiconductor radiation measuring device according to the first embodiment of the present invention, and FIGS. 9 and 10 are equivalent circuit diagrams for explaining the operation of the first embodiment. , FIG. 11 is a block diagram of a preamplifier for a semiconductor radiation measuring device according to a second embodiment of the present invention, FIG. 12 is a block diagram of a third embodiment of the present invention, and FIG. It is a block diagram of a 4th Example. (1)...Semiconductor detection kg, (3)...Preamplifier, OQ...Inverting amplifier, OQ...Feedback resistor Rf',
(lη...Feedback resistance Rf'', +18)...Feedback resistance Rv, (11...Frequency characteristic correction capacitance Cv, (1)
...Feedback resistance R, //4shiυ...Feedback resistance Rv', @
...Frequency characteristic correction capacitance Cv' Agent Yoshihiro Morimoto (28) Hehehe Hee Sa-q Sami Kuwa+11+I+ -1 -I -ノ -IFigure 3 Rf Figure 4 (j) Figure 5 Fig. 7 Fig. 1 Fig. β Fig. Vp Section 9 Fig. 1 θ Fig. 11 v Fig. 12 D Cv' Fig. 13 -

Claims (1)

[Claims] 1. A semiconductor radiation preamplifier in a radiation measuring device using a semiconductor detector, which is composed of a high gain inverting amplifier and feedback means for feeding back the output of the inverting amplifier to the input side. Preamplifier for measuring equipment. 2. The preamplifier for a semiconductor radiation measuring device according to claim 1, wherein the feedback means is a resistor that feeds back the output of the inverting amplifier to the input side. 3. The feedback means feeds back the output of the inverting amplifier to the input, and is composed of first and second resistors connected at one end and a capacitor that varies the amount of feedback according to the same wave number, and one end of the capacitor is connected to the first resistor. 1. Claim 1, characterized in that it is connected to the connection point of the second resistor, and the other end is grounded.
Prefix for the semiconductor radiation measuring device described in Section (1) l Amplifier. 4. The feedback means feeds back the output of the inverting amplifier to the input, and is composed of first and second resistors connected at one end and a capacitor that varies the amount of feedback depending on the frequency, and one end of the capacitor is connected to the input of the inverting amplifier. 2. The preamplifier for a semiconductor radiation measuring device according to claim 1, wherein the other end of the preamplifier is connected to a connection point between the first and second resistors on the output side. 5. The feedback means feeds back the output of the inverting amplifier to the input, and is composed of first and second resistors connected at one end, and first and second capacitors that vary the amount of feedback depending on the frequency. One end of the first capacitor is connected to the connection point between the first and second resistors, the other end is grounded, one end of the second capacitor is connected to the output side of the inverting amplifier, and the other end is connected to the connection point of the first and second resistors. ,
2. The preamplifier for a semiconductor radiation measuring device according to claim 1, wherein the preamplifier is connected to a connection point of the second resistor.