JPH02102462A - Pulse frequency detecting circuit - Google Patents

Abstract

PURPOSE:To accurately measure a pulse frequency even when the number of pulse signals is large by providing a voltage amplifier, a voltage comparator, and a counter. CONSTITUTION:This circuit is connected to a capacitor 5 and a switch 21 in parallel and provided with the voltage amplifier 3 which outputs a voltage corresponding to the number of inputted pulse signals and the voltage comparator 23 which is connected to the output side of the amplifier 3 and turns on the switch 21 temporarily when its output value reaches a prescribed value. Further, a counter 8 which is connected to the output side of the comparator 23 and counts the output signal of the comparator 23 is provided. Then, the switch 21 connected to a charge voltage converter in parallel is turned on and off to output a voltage corresponding to the number of pulse signals inputted to the amplifier 3 from the amplifier 3. Consequently, the frequency of operation of the comparator 23 and counter 8 is decreased greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a circuit for detecting the frequency of optical pulses such as X-rays.

(Prior Art) X-ray detection devices are installed in X-ray devices used for medical purposes and other purposes, industrial non-destructive inspection devices, etc. The photon counting method ( There is a method called the time-correlated single photon counting method, which counts the number of incident X-ray photons and attempts to obtain a grayscale image using this count. The obtained data is particularly advantageous in that it contains no errors other than theoretically predicted statistical fluctuations, and in principle the S/N can be made infinite.

FIG. 4 shows a pulse frequency detection circuit according to the above method, in which the output side of a detector (2) for detecting X-rays (1) is connected to a voltage amplifier (3). This voltage amplifier (3)
A waveform shaping filter (4) for removing noise is connected to the output side of the voltage amplifier (3), and a capacitor (5) is connected in parallel to the voltage amplifier (3). The output side of the waveform shaping filter (4) is connected to one input of a voltage comparator (6), and the other input of the voltage comparator (6) is connected to an external voltage source (7). Also, this voltage comparator (
A counter (8) is connected to the output side of 6).

Next, the operation will be explained. When one pulse signal from the detector (2) that has detected one X-ray photon of the X-ray (1) is input to the voltage amplifier (3), this voltage amplifier (3) receives this pulse signal (one pulse). Amplify and output. After noise is removed from this output signal by a waveform shaping filter (4), the output signal is sent to an external voltage source (7) by a voltage comparator (6).
) is compared with the threshold value (Vrar) of . By repeating the above operations and detecting the pulse frequency, the number of X-ray photons is counted, and a grayscale image is formed based on the counted value.

[Problem to be solved by the invention]

However, in order to obtain a high-gradation image using the above circuit, it is necessary to count a large number of X-ray photons, especially when there is a limit on the measurement time such as when capturing moving images. , it is necessary to significantly increase the number of counts per unit time, which places a large burden on the detector (2) and the signal processing circuit. For example, when trying to obtain an image with 100 gradations in 1 ounce imaging time, approximately 10
Five X-ray photons must be counted within this time. That is, high-speed counting is required once every 100 ns on average, which is quite difficult considering the response speed of the detector (2) or the frequency characteristics of the analog circuit at the subsequent stage.

Furthermore, in order to improve the image resolution (number of gradations) by one order of magnitude, it is necessary to increase the photon count rate by two orders of magnitude, which makes it extremely difficult to increase the gradation of moving images using the conventional circuits described above. Ta.

The present invention was made to solve such problems,
It is an object of the present invention to provide a pulse frequency detection circuit that can accurately measure pulse frequency even when the number of pulse signals per time is large.

[Means to solve the problem]

The pulse frequency detection circuit according to the present invention includes a voltage amplifier that is connected in parallel to a capacitor and a switch and outputs a voltage according to the number of input pulse signals, and a voltage amplifier that is connected to the output side of this voltage amplifier and that is A voltage comparator that outputs a signal to temporarily immerse the switch when the output value reaches a predetermined value, and a counter that is connected to the output side of the voltage comparator and counts the output signal of the voltage comparator. It is something.

(Function) Conventionally, waveforms were separated and counted one by one, but in the present invention, the pulse signal input to the voltage amplifier is controlled by the on/off operation of a switch connected in parallel to the charge-voltage converter. A voltage having a strength corresponding to the number of signals can be output from the voltage amplifier.Thereby, the number of operations of the voltage comparator and counter can be significantly reduced.

(Example) An example of the present invention will be described below based on FIGS. 1 to 3. As shown in Figure 1, a detector (
The output side of 2) is connected to a voltage amplifier (3). This voltage amplifier (3) is designed to output a voltage whose strength corresponds to the number of manually inputted pulse signals, and the capacitor (5) and switch (21) are connected to this voltage amplifier (3).
) are connected in parallel. The voltage amplifier (3) and the capacitor (5) constitute a charge-voltage converter (22) that converts the charge output from the detector (2) into a voltage signal. In this embodiment, an analog switch is used as the switch (21). A voltage comparator (23) is connected to the output side of the voltage amplifier (3), which outputs a signal to temporarily turn on the switch (21) when the output value of the voltage amplifier (3) reaches a predetermined value. In this embodiment, in order to set the above predetermined value, a voltage amplifier (3) is connected to one of the human power sources (24), and an external voltage source (26) is connected to the other human power source (25). There is. The output side of the voltage comparator (23) is connected to the control input of the switch (21) for operating the switch (21), and also connected to a counter (8) for counting the output signal of the voltage comparator (23). ) is also connected. In this embodiment, a binary counter is used as the counter (8).

Next, the operation will be explained. FIG. 2 is a diagram showing the response of the charge-voltage converter (22) to one X-ray photon, where time is t and the output of the charge-voltage converter (22) is u (t
), as shown in the figure, when one X-ray photon is incident, the output of the converter (22) once becomes So, and then gradually decreases as shown by the curve shown in equation (1) below.

−U (t) = Soe”
...(1) However, in So, the constant is conventionally counted as the number of changes in the output of the converter (22) for one X-ray photon as shown in Figure 2, so the number of counts was very large. It had become.

On the other hand, in this embodiment, instead of separating the waveforms one by one, a large number (for example, 100
When the waveform (31) of the output of the converter (22) generated by the incidence of X-ray photons (~200 pieces) reaches a predetermined value,
The output signal of the voltage comparator (23) is configured to be inverted.

First, in the initial state, the output of the charge voltage converter (22) is u
(0) = O1 The output of the voltage comparator (23) is “L” (or 0
)'', the switch (21) is assumed to be off. If X X-ray photons are incident on the detection circuit in this state per unit time, the converter output u (t) changes according to equation (2), which forms the above waveform (31).

Engineering L u(t) = uo(x)' (t-eT:)
・(2) u (t) increases monotonically with time t, and eventually reaches the predetermined threshold value v,,r of the voltage comparator (23)
= Exceeds h. Let this time be 1=10. Then,
As shown in FIG. 3(b), the output of the voltage comparator (23) becomes "L (or O) J to rH (or 1)", which turns on the switch (21) momentarily. The capacitor (5) is rapidly discharged and u (t) becomes u(t)=O. At this time, the output of the voltage comparator (23) is again rl, J
At the same time, the count "1" is recorded in the counter (8). This operation is repeated every time u(t)=h, and the number of times the voltage comparator (23) operates is recorded in the counter (8) as the final count number.

That is, the relationship between the frequency X of incident photons and the output count number 2 is given by equation (3).

z = 1 / t 0 ・
...(3) However, t. is the solution of the following equation (4) by substituting 70 for t in equation (1).

Therefore, in this embodiment, a high-gradation X-ray image can be captured using a relatively slow system (sensor, signal processing circuit).

Furthermore, in this embodiment, in a system in which the amount of X-rays incident on a unit time is relatively large, the dose of the incident X-rays can be measured with high accuracy, and the system components can be used at relatively low speeds. Furthermore, since the number of circuit operations is small, power consumption is low, and the circuit configuration is also simple.

As described above, since the present invention is characterized by a simple circuit configuration, it is also effective as a circuit for an array sensor or, by expanding a little more, as a circuit for a second-order planar array sensor.

Although the above embodiments have been described with respect to the case of X-rays, other light pulses such as visible light, infrared rays, laser light, etc. may also be used.

(Effects of the Invention) As explained above, the present invention connects a capacitor and a switch in parallel to a voltage amplifier, and when a plurality of pulse signals are input and the output value of the voltage amplifier reaches a predetermined value, the output signal of the voltage comparator changes. Since the switch is reversed and turned on temporarily, the number of operations of the voltage comparator and counter can be significantly reduced, allowing accurate measurement of pulse frequency even when the number of pulse signals is large. can do.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing one embodiment of the present invention. Figure 1 is a circuit diagram, Figure 2 is a graph showing the response of a charge-voltage converter to one X-ray photon, and Figure 3 is a graph showing a large number of FIG. 4 is a graph showing an example of the response of the embodiment circuit to X-ray photons, and FIG. 4 is a circuit diagram showing a conventional pulse frequency detection circuit, corresponding to FIG. ...voltage amplifier, ...capacitor, ...counter, 21) ...switch, 23) ...voltage comparator. Note that the same reference numerals in each figure indicate the same or equivalent parts.

Claims (1)

[Claims] A voltage amplifier is connected in parallel to the capacitor and the switch and outputs a voltage according to the number of input pulse signals, and the voltage amplifier is connected to the output side of the voltage amplifier, and when the output value of the voltage amplifier reaches a predetermined value, the switch is turned on. 1. A pulse frequency detection circuit comprising: a voltage comparator that outputs a signal for temporarily turning on the pulse; and a counter connected to the output side of the voltage comparator and counting the output signal of the voltage comparator.