JPH05119157A - X-ray detector - Google Patents

Abstract

PURPOSE:To prevent influence by switching noise by driving a digital circuit part by a synchronization signal from outside and driving a potential-voltage converter only while the digital circuit part is not driven. CONSTITUTION:An output of a potential outputting type detector 1 is input to a potential-voltage converter 2, and the output is led to a voltage comparator 3. Reference voltage Vref for discriminating from noise is set in the comparator 3, and when the output from the converter 2 exceeds this level, a logic level pulse signal is output to be introduced to a counter 4 to be counted. A synchronization clock phi is inputted from outside into the converter 2, the comparator 3 and the counter 4, by which operation of each of these circuits is regulated. That is, while the converter 2 performs conversion and holding operations, the comparator 3 and the counter 4 being a digital circuit part do not operate. Therefore during conversion and holding operations, a signal to cause noise is not generated from the digital circuit part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photon counting type X-ray detection device that can be used in medical X-ray imaging devices, industrial nondestructive inspection devices, and the like.

[0002]

2. Description of the Related Art FIG. 5 shows a basic circuit configuration of a conventional photon counting type X-ray detector using a charge output type X-ray detector, and FIG. 6 shows an operation explanatory diagram thereof.
The charge (current) output signal (a) from the detector 51 is converted into a step-like pulse (b) by the charge-voltage converter 52. The output signal of the charge-voltage converter 52 is filtered by the filter 53 into a pulse signal as shown in (c) and then input to the voltage comparator 54. A voltage level V _ref for discriminating noise is preset in the voltage comparator 54, and this set level V _ref is set.
_A pulse signal that exceeds _ref is amplified to a logic level and input to a counter 55 as shown in (d), and the count value of the counter 55 is configured to represent the dose of X-rays incident on the detector 51. There is.

[0003]

According to the conventional detection device as described above, the digital circuit portion (voltage converter 54
In the following), the voltage has a logic level of, for example, about 5V, whereas in the analog circuit part, the operation of the voltage comparator 54 becomes random in time under the situation where it is necessary to compare voltage signals on the mV order. Therefore, when a large number of sets of the circuits shown in FIG. 5 are integrated on the substrate, there is a problem that switching noise of the digital circuit portion is mixed into the analog circuit portion as random noise.

It is an object of the present invention to provide an X-ray detection device which can always perform accurate detection without the influence of switching noise from the digital circuit part on the analog circuit part even if it is highly integrated.

[0005]

In order to achieve the above object, in the X-ray detection apparatus of the present invention, the voltage comparator and the counter are driven by a synchronization signal from the outside, and the charge-voltage converter is driven by the voltage. It is configured to operate only when the comparator and the counter are not driven.

[0006]

A digital circuit is driven by driving a voltage comparator and a counter, which are digital circuit parts, at a constant timing by a synchronizing signal from the outside, and driving a charge-voltage converter only when the digital circuit part is not driven. It is guaranteed that the switching noise of the portion will be mixed into the analog circuit portion after the voltage comparison is completed, and the switching noise from the digital circuit portion will not affect the voltage comparison result.

[0007]

Embodiment FIG. 1 is a block diagram showing a circuit configuration of an embodiment of the present invention. The output of the charge output type detector 1 is input to the charge-voltage converter 2. The output of the charge-voltage converter 2 is guided to the voltage comparator 3. A reference voltage V _ref for discriminating against noise is set in the voltage comparator 3,
When the output of the charge-voltage converter 2 exceeds the set level V _ref , the voltage comparator 3 outputs a pulse signal of logic level. The output of the voltage comparator 3 is introduced into the counter 4 and counted.

The above charge-voltage converter 2 and voltage comparator 3
A synchronous clock φ is externally introduced to the counter 4 and the operation of each of these circuits is regulated by the synchronous clock φ as described below. FIG. 2 is a time chart showing an example of the signal waveform of each part. The synchronous clock φ is at the H level for the period T _{0 in the} cycle T, but the charge-voltage converter 2 performs the conversion operation and holds the output voltage only when the synchronous clock φ is at the L level, and φ is at the H level. At the time of, the voltage value held is reset.

The voltage comparator 3 is triggered by the rising edge of the synchronous clock φ to perform voltage comparison, and the output based on the comparison result is held until the next rising edge of the clock. Further, the counter 4 is adapted to perform the counting operation at the falling edge of the synchronous clock φ.

By the operation of each section as described above, the signal generated by the incidence of radiation on the detector 1 during the period of the synchronous clock φ being L is compared at the first rising edge of φ, and the set level V _{ref is} set. Those exceeding the value will be counted by the counter after the time T ₀ has further elapsed. In other words, while the charge-voltage converter 2 is performing the conversion operation and the holding operation, the voltage comparator 3 and the counter 4, which are digital circuit parts, do not operate, and therefore, the digital circuit during the conversion operation or the holding operation. No signal that causes noise is generated from the part.

When a large number of sets of the circuit shown in FIG. 1 are integrated on a substrate by driving each channel with the same clock φ, the digital circuit portion in each channel operates. It is possible to avoid the situation in which the noise from the digital circuit portion is mixed in before the comparison is started and the error is generated in the comparison result after the voltage comparison operation is completed in the channel.

By the way, in the above embodiment, there is a drawback that the X-rays incident on the detector 1 cannot be counted during the reset period of the charge-voltage converter 2, that is, during the period when the clock φ is H. .. FIG. 3 is a block diagram showing the circuit configuration of another embodiment of the present invention, and the above-mentioned drawbacks can be eliminated by the configuration of this embodiment.

[0013] In this example, with respect to one detector 1, a 2 system voltage converter - comparator circuit system provided, it synchronizes each strain from each other, and the two phase shifted clocks phi ₁ and It is driven by φ ₂ . That is, the output of the detector 1 is introduced into both the first and second charge-voltage converters 21 and 22, and the output of each charge-voltage converter 21 and 22 is respectively the first and second voltage comparators. It is configured to be input to 31 and 32. The outputs of the first and second voltage comparators 31 and 32 are counted by the single counter 4 via the OR gate 30 and summed.

FIG. 4 is a time chart showing an example of the signal waveform of each part of this embodiment. First charge-voltage converter 2
1 and the first voltage comparator 31 generate the first synchronous clock φ ₁
The second charge-voltage converter 22 and the second voltage comparator 32 are driven by the second synchronous clock φ.
Driven by _two . The first and second synchronous clocks φ ₁ and φ ₂ are both at the H level for the period T _{0 in the} cycle T, but they are out of phase with each other by T ₀ + T _S.

The first charge-voltage converter 21 performs the conversion operation and holds the output voltage only when φ ₁ is at L level or L level, and when φ ₁ is at H level, the held voltage value is held. It is configured to reset. The first voltage converter 31 is triggered by the rise of φ ₁ to perform the voltage comparison, and the output based on the comparison result is held until the next rise of the clock φ ₁ .

Further, the second charge-voltage converter 22 and the second voltage comparator 32 are also driven by the clock φ _{2 at the} same timing as above. The counter 4 is adapted to perform the counting operation at the falling edge of the clock φ ₂ . According to the above-described embodiment, even when X-rays are incident on the detector 1 during the reset period of the first charge-voltage converter 21 (while the clock φ ₁ is at the H level), the second charge Since the charge-voltage converter 22 is in operation, its detector output will be normally counted by the counter 4. Here, the switching signals of the first voltage comparator 31 and the counter 4 are generated during the operation period of the second charge-voltage converter 22, and the holding voltage of the second charge-voltage converter 22 is The comparison is at the rising edge of φ ₂ , and φ
_Between the falling edge of _{1 and} the rising edge of φ ₂ , the time T _S
Therefore, even if spike noise is added to the output of the second charge-voltage converter 32 at the time of the rise or fall of φ ₁ , it does not affect the output voltage comparison result. ..

Further, the charge-voltage converters 21 to 22 are provided.
Rising even slower if the Kurroku phi time from ₁ falling to rising of phi ₂ T _S (and phi times from ₂ falling to phi ₁ rising), greater than the rise time of these transducers If you do
The original voltage value is input to at least one of the voltage comparators, and correct voltage comparison can be performed.

[0018]

As described above, according to the present invention, switching in the digital circuit portion is performed at regular time intervals regulated by an external synchronization clock,
Moreover, since the noise due to this switching comes after the voltage comparison is completed, even if the analog circuit part and the digital circuit part are densely integrated on the substrate, the noise that affects the voltage comparison is not affected. It has become possible to always carry out accurate dose measurements.

Further, according to the present invention, most of the circuit consumes only the current transiently, so that there is also an advantage that an X-ray detection apparatus with extremely low power consumption can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of the present invention.

FIG. 2 is a time chart showing an example of signal waveforms of respective parts.

FIG. 3 is a block diagram showing a circuit configuration of another embodiment of the present invention.

FIG. 4 is a time chart showing an example of a signal waveform of each part.

FIG. 5 is a block diagram showing a basic circuit configuration of a conventional photon counting type X-ray detector using a charge output type X-ray detector.

FIG. 6 is an operation explanatory view showing an example of signal waveforms of respective parts.

[Explanation of symbols]

1 ... Detector 2,21,22 ... Charge-voltage converter 3,31,32 ... Voltage comparator 4 ... Counter 30 ... OR gate φ, φ ₁ , Φ ₂ ... Synchronous clock

Claims (1)

[Claims] 1. A charge output type X-ray detector is connected to a charge-voltage converter having a function of holding an output voltage for a certain period of time, and the output of the charge-voltage converter is led to a voltage comparator. In an apparatus in which the presence or absence of X-ray particles is determined and the output of the voltage comparator is introduced into a counter, the voltage comparator and the counter are driven by a synchronization signal from the outside and the charge-voltage The X-ray detection device, wherein the converter is configured to perform the conversion and holding operations only when the voltage comparator and the counter are not driven.