JPH058993B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a baseline stabilization circuit for the output of an amplifier circuit, such as a detection signal of a radiation detector, for example. (Prior art) For example, since the detection signal of a radiation detector used for radiation measurement generally consists of irregular minute pulse signals, when using a DC amplifier to amplify this signal, input offset voltage or temperature drift, etc. As a result, the baseline fluctuates, and in some cases, the output voltage saturates at a voltage determined by the power supply voltage, making it impossible to accurately determine the peak value of the pulse signal to be produced in either case. When using an AC amplifier as an amplifier, the average value of the amplified output is a characteristic of the AC amplifier, so if the number of pulses is extremely small, the peak value of the pulse can be determined almost accurately, but if the number of pulses is large, As the value increases, the base line fluctuates and falls, and the pulse height value tends to become smaller than the correct value. In order to eliminate the above-mentioned drawbacks when the detection signal of a radiation detector is amplified by a DC or AC amplifier, a baseline stabilization circuit as shown in FIG. 9, for example, has been proposed and implemented. In the figure, TI is the input terminal of the amplified signal, A
Reference numeral 1 designates an operational amplifier, and resistors R1, R2, and R9 are selected to appropriate values to keep the degree of amplification substantially constant. C4 is a coupling capacitor, T0 is an output terminal,
The FET is a normally closed switching element made of, for example, a field effect transistor, and the MUL is its switching control circuit, which is made of, for example, a monostable multivibrator. TTI is an input terminal for timing pulse signals. When this circuit is used, for example, to stabilize the baseline in the amplified output when amplifying the detection signal of a radiation detector, the detection signal of the radiation detector is transferred to a differentiator circuit and a main amplifier (none of which are shown). In addition, waveform shaping is performed in the main amplifier, that is, the time width of the pulse signal to be detected in the detection output is appropriately limited to a fixed time (for example, 1 μsec. to several μsec.).
without the subsequent detection target pulse signal being superimposed on the falling or rising part of the preceding detection target pulse signal.
After waveform shaping is performed so that each pulse signal to be detected can be separated, it is applied to the input terminal TI. While the detection signal of the radiation detector does not include the pulse signal to be detected, the coupling capacitor C4 provided on the output side of the operational amplifier A1 is kept in a grounded state via the normally closed switching element FET, and the output terminal T0 No output appears in . When the radiation detector detects a pulse signal to be detected, the amplified output whose waveform has been shaped by the main amplifier is applied to the input terminal TI, and detection is performed according to the polarity of the pulse signal to be detected, which is determined by the detection characteristics of the radiation detector. A differential pulse signal synchronized with the rise or fall of the target pulse signal is taken out from the differentiator circuit and applied to the monostable multivibrator MUL via the input terminal TTI. In response to this differential pulse signal, the monostable multivibrator MUL oscillates, and its oscillation output opens the field effect transistor FET, and the output signal of the operational amplifier A1 is taken out via the coupling capacitor C4 and the output terminal T0. The time width of the oscillation output of the monostable multivibrator MUL, and therefore also the field effect transistor
If the open time width of the FET is made to match the time limit for waveform shaping in the main amplifier, only the pulse signal to be detected out of the output of the operational amplifier A1 will be taken out from the output terminal T0, and the By appropriately selecting the capacitance, noise components superimposed on the pulse signal to be detected can be removed. At the same time as the detection target pulse signal disappears, the field effect transistor FET is also closed, and the output of the output terminal T0 becomes zero. (Problems to be Solved by the Invention) In the conventional baseline stabilization circuit shown in FIG.
If the impedance of the load connected to is low, the waveform of the detection target pulse signal taken out via the coupling capacitor C4 will be distorted, making it impossible to determine the correct peak value. Also, when the noise component is relatively small compared to the pulse signal to be detected, the baseline stabilizes to some extent, but when the noise component is relatively large compared to the pulse signal to be detected, the baseline stabilizes. Almost no stabilizing effect was observed. (Means for Solving Problems, Embodiments) In addition to the above-mentioned drawbacks of the conventional art, the present invention can solve the problem even when a relatively high-level noise component is mixed in with respect to the peak value of the pulse signal to be detected. The purpose of this invention is to realize a baseline stabilization circuit that can determine the correct peak value of a pulse signal to be detected. FIG. 1 is a diagram showing an embodiment of the present invention.
is the input terminal of the signal to be amplified, A1 is the operational amplifier,
The values of resistors R1 and R2 are appropriately selected to keep the amplification level approximately constant. T0 is the output terminal, FET
is a normally closed switching element, for example consisting of a field effect transistor. MUL is the opening/closing control circuit, which consists of, for example, a monostable multivibrator. A2 is an operational amplifier, which together with resistors R3 and R4 and capacitor C1 forms a voltage holding circuit.
TTI is an input terminal for timing pulse signals. In the circuit of the present invention, the field effect transistor FET is always kept closed, and the operational amplifier A
The voltage at point A on the output side of the voltage holding circuit consisting of 2 is kept equal to the voltage at the inverting input terminal of operational amplifier A1. Similar to the conventional circuit shown in FIG. Assuming that the waveform is as shown in Figure A, while the pulse signal to be detected is not detected, the input signal is introduced into the voltage holding circuit consisting of the operational amplifier A2 via the operational amplifier A1, the field effect transistor FET, and the input resistor R3. and its output voltage is applied to operational amplifier A1
It is applied to the non-inverting input terminal of , and is differentially combined with the input signal applied to the inverting input terminal, and does not appear as an output at the output terminal T0. However, when the pulse signal to be detected is detected from the radiation detector, a differential pulse signal (FIG. 4, b) synchronized with the rising or falling edge of the pulse signal to be detected is sent out from the differentiating circuit according to the polarity of the pulse signal to be detected. It is applied to the monostable multivibrator MUL via the input terminal TTI to cause it to oscillate.
If the time width of the oscillation output of the monostable multivibrator MUL is adjusted to be equal to the time width of the waveform-shaped pulse in the main amplifier, the field effect transistor FET is opened only during this time width (the fourth During this opening, the voltage holding circuit continues to hold the voltage immediately before the field effect transistor FET was opened (FIG. 4, d). Therefore, the noise component superimposed on the detection target pulse signal applied to the inverting input terminal of the operational amplifier A1 via the input terminal TI is differentially synthesized with the holding voltage of the voltage holding circuit, and the noise component is The detection target pulse signal from which the component has been removed is taken out from the output terminal T0 (FIG. 4, E). In addition, each horizontal axis of FIG. 4A to 4E represents time T, and each vertical axis represents voltage V. In this example, a field effect transistor
If the level of the noise component changes significantly while the FET is open, the noise component will not be completely compensated, and there is a possibility that the correct peak value of the pulse signal to be detected cannot be determined. To explain this in terms of waveform diagrams, Fig. 5 (horizontal and vertical axes are the same as Fig. 4) is an enlarged waveform diagram from time t1 to t2 in Fig. 4. 1 is the signal waveform applied to the inverting input terminal of the operational amplifier A1, 2 is the differential pulse signal waveform synchronized with the pulse signal to be detected, 3 is the waveform indicating the open/close state of the field effect transistor FET, and d is the holding voltage of the voltage holding circuit. The waveform and E show the output voltage waveform of the output terminal T0.As is clear from each figure, when the detection target pulse signal is detected, the holding voltage in the voltage holding circuit is constant, but the level of the noise component is is fluctuating during this time, and therefore, it is impossible to compensate for the fluctuation of this noise component using the holding voltage just before the field effect transistor FET is opened, and the output terminal T0
The waveform of the pulse signal to be detected extracted from the detection target pulse signal will be different from the actual waveform, and there is a possibility that it will not be possible to obtain the correct peak value. FIG. 2 is a diagram showing an example of the circuit of the present invention that can completely compensate for level fluctuations of noise components while the field effect transistor FET is open. R5 and C2 are a resistor and a capacitor forming an integrating circuit. , other symbols and configurations are the same as in FIG. FIG. 6 (horizontal and vertical axes are the same as FIG. 4) is a waveform diagram for explaining the operation. Although not shown in the figure as in the case of the previous embodiment, for example, the detection signal of the radiation detector is applied to the main amplifier and the differential circuit, and after the main amplifier performs the same waveform shaping as described above, the input terminal TI is When applied to the inverting input terminal of operational amplifier A1 through
The inverted amplified output is applied to a voltage holding circuit consisting of an operational amplifier A2 via a field effect transistor FET. The output voltage of the voltage holding circuit is applied to the operational amplifier A via an integrating circuit consisting of a resistor R5 and a capacitor C2.
1 to the non-inverting input terminal, and this terminal voltage,
That is, the voltage at the connection point C between the resistor R5 and the capacitor C2 (FIG. 6, e) is kept equal to the voltage at the inverting input terminal of the operational amplifier A1 (FIG. 6, a), and the output voltage at the output terminal T0 It operates so that becomes zero. Note that FIG. 6D shows the voltage waveform at point B on the output side of the voltage holding circuit, which is a differential waveform of the voltage waveform at point C. When a pulse signal to be detected is sent out from the radiation detector, a differential pulse signal (FIG. 6, b) synchronized with its rising or falling edge is sent out from the differentiating circuit,
A timing pulse signal is applied to the monostable multivibrator MUL through the input terminal TTI, causing it to oscillate and opening the field effect transistor FET for a certain period of time (Fig. 6, C). Holding the voltage immediately before the effect transistor FET is opened is the same as in the previous embodiment, but in this embodiment, the voltage held by the voltage holding circuit is integrated by an integrating circuit consisting of a resistor R5 and a capacitor C2, and the voltage held by the operational amplifier A1 is The difference voltage between the input signal introduced into the non-inverting input terminal and applied to the inverting input terminal, that is, the detection target pulse signal (sixth
(F) is taken out from the output terminal T0. FIG. 3 also shows another embodiment of the present invention,
A3 is an operational amplifier, which forms an integration circuit together with resistors R6, R7 and capacitor C3. R8 is an input resistor, R9 is an operational resistor, and the other symbols and configurations are the same as in FIG. In this embodiment, the integrating circuit formed by resistor R5 and capacitor C2 in the previous embodiment is replaced with an integrating circuit consisting of operational amplifier A3, resistors R6, R7, and capacitor C3, and the output signal of this integrating circuit (inverse to the input signal) is This embodiment differs from the previous embodiment only in that it is configured to apply the phase) to the inverting input terminal of the operational amplifier A1 via the input resistor R8, and the baseline stabilization operation is the same as that of the previous embodiment. (Effects of the Invention) Since the circuit of the present invention can lower the output impedance, there is no fear that the waveform of the pulse signal to be detected will be distorted even when the impedance of the load connected to the output terminal T0 is low. In particular, in the embodiments shown in FIGS. 2 and 3, there is no fear that the coupling capacitor becomes a load on the operational amplifier A1 and is likely to cause oscillation. In particular, in the embodiments shown in FIGS.
Even if the noise component fluctuates significantly while the FET is open, it can be almost completely compensated for.This can be explained using a waveform diagram as shown in Figure 7 (horizontal and vertical axes are shown in Figure 4). ) is a waveform diagram expanded between time t1 and t2 in FIG. 6 between the axes, and A is the inverting input of the operational amplifier A1 in the baseline stabilization circuit of the present invention shown in FIGS. 2 and 3. Input signal waveform applied to the terminal, b is input terminal TTI
The differential pulse signal waveform introduced into C is a normally closed switching element consisting of a field effect transistor.
Waveform showing open/closed state of FET, D is operational amplifier A
The voltage waveform at point B on the output side of the voltage holding circuit consisting of 2, E is the voltage waveform at the connection point C between resistor R5 and capacitor C2, (the waveform at point C in Figure 3 is in reverse phase with the waveform at E). ) and F are the detection target pulse signal waveforms taken out from the output terminal T0. As shown in the figure, since waveform E is an integral waveform of waveform D, by appropriately selecting the time constant of the integrating circuit shown in FIGS. 2 and 3, the The rate of change in voltage at point C is kept almost the same as the rate of change in voltage at point C before the field effect transistor FET is opened, and therefore the change in voltage at point C while the field effect transistor FET is open is considered to be the change in the level of the noise component. Since it can be done almost in the same way as above, the pulse signal to be detected taken out from the output terminal T0 is almost unaffected by noise components, and an accurate peak value can be obtained. To explain the effect of the present invention circuit on baseline stabilization based on the experimental results conducted by the present inventors on a prototype circuit, in Fig. 8, PG is a pulse generator, NG is a noise voltage generator, and MA is a main amplifier. ,
DF is differentiator circuit, BLR is baseline stabilization circuit, PHA
is a pulse height analyzer, and the results of measuring the variation in the peak value of the pulse signal to be detected when the baseline stabilization circuit BLR is configured with the circuits of the embodiments shown in Figures 1 and 2 are shown in the table below. It was shown to.

[Table] The above table shows the noise voltage generator NG with 200
While generating sine wave voltage of Hz and 1kHz,
This is data when the generated voltage is varied from 0.01 V to 10 V, and a pulse signal with a peak value of 1 V is generated in the pulse generator PG as the pulse signal to be detected. As is clear from the above table, the baseline stabilizing circuit of the present invention has a very remarkable baseline stabilizing effect. Although the present invention has been described above for stabilizing the baseline in a detection signal amplification circuit of a radiation detector, it is of course applicable to stabilizing the baseline in a general pulse signal amplification circuit.

[Brief explanation of the drawing]

1 to 3 are diagrams showing one embodiment of the present invention, FIGS. 4 to 7 are waveform diagrams for explaining its operation, and FIG. 8 is for explaining the effects of the present invention. , and FIG. 9 are diagrams showing conventional circuits, in which TI and TTI: input terminals, A1 to A3: operational amplifiers,
R1 to R9: Resistance, T0: Output terminal, FET:
Switching element, MUL: Opening/closing control circuit, C1
to C4: capacitor, PG: pulse generator,
NG: noise voltage generator, MA: main amplifier, DF: differentiation circuit, BLR: baseline stabilization circuit, PHA: pulse height analyzer.

Claims (1)

[Scope of Claims] 1. An operational amplifier to which a main amplifier output is applied that limits the time width of a pulse signal to be detected to a constant value, and a voltage holding circuit to which the operational amplifier output is introduced via a normally closed switching element. A circuit for negative feedback of the holding voltage of the voltage holding circuit to the operational amplifier, and a switching element driven by a signal synchronized with the pulse signal to be detected, and opening the normally closed switching element for the time width of the pulse signal to be detected. A baseline stabilization circuit comprising a control circuit. 2. An operational amplifier to which the output of the main amplifier is applied that limits the time width of the pulse signal to be detected to a constant, a voltage holding circuit to which the output of the operational amplifier is introduced via a normally closed switching element, and a holding circuit for this voltage holding circuit. an integrating circuit that integrates a voltage and provides negative feedback to the operational amplifier; and an opening/closing control circuit that is driven by a signal synchronized with the pulse signal to be detected and opens the normally closed switching element for a time width of the pulse signal to be detected. A baseline stabilization circuit characterized by comprising: