JP5716584B2 - X-ray detector - Google Patents

Description

  The present invention relates to an X-ray detector used in an X-ray analyzer or the like.

  FIG. 4 is a configuration diagram of a conventional X-ray analyzer. The X-ray analyzer shown in FIG. 4 includes an X-ray sensor 1, a preamplifier 2, a cable 4, a differential amplifier 5, and an AD converter (ADC) 6.

  The X-ray sensor 1 detects incident X-rays by converting incident X-rays into charge information by an X-ray conversion layer (semiconductor layer) and reading the converted charge information. The preamplifier 2 includes a low-noise JFET (junction FET) 21, a feedback capacitor 22, and an amplifier 23, and amplifies a minute analog signal from the X-ray sensor 1.

  The amplified analog signal has a staircase waveform as shown in FIG. 5A. As shown in the enlarged view of FIG. 5B, the peak value wh of one step corresponds to the energy of the incident X-ray. To do. The discrimination circuit 8 turns on the transistor Tr1 when the output of the preamplifier 2 exceeds a predetermined value. For this reason, since the gate of JFET 21 is connected to the ground GND, the staircase waveform returns to the lowest value.

  Further, the analog signal from the preamplifier 2 is sent to the AD converter 6 via the cable 4 and the differential amplifier 5, and is converted into a digital signal by the AD converter 6. Since the X-ray sensor 1 and the preamplifier 2 (hereinafter referred to as an X-ray detector) have high impedance, they are easily affected by radiation noise. Further, since the cable 4 serves as an antenna, it picks up radiation noise and increases the internal noise of the preamplifier 2 or degrades the analog signal waveform.

  Then, the following two methods are disclosed as a method of reducing radiation noise. In the first method, the X-ray detection unit is electrically shielded by the shield unit 7 as shown in FIG. Generally, electrical noise can be reduced by sealing the antenna portion with a grounded metal shield material. Moreover, as described in Patent Document 1, the shielding effect can be further improved by using conductive fibers obtained by folding polyamide and silver as the shielding material.

  Further, as described in Patent Document 2, magnetic noise can be reduced by using a magnetic shield formed of a magnetically permeable material typified by permalloy or the like.

  In the second method, as shown in FIG. 4, a coaxial cable is used as the cable 4 and the input portion of the AD conversion board 9 is configured by the differential amplifier 5 to reduce radiation noise.

  As another conventional technique, Patent Literature 3 is disclosed.

JP 2000-116633 A JP 2005-249658 A Japanese Patent No. 3340801

  However, the noise current generated by picking up the radiation noise generated in the GND line of the cable 4 flows to the SGND (signal ground) of the preamplifier 2 from the noise path shown in FIG. And the resolution decreases.

  In addition, a GND loop is formed between the SGND line and the power supply GND or FGND, a noise current is generated due to the influence of the externally varying magnetic field, and the analog signal waveform deteriorates. For this reason, in order to reduce the influence of the noise current, a measure for increasing the signal gain can be considered.

  However, although the amplitude of the analog signal is limited by the maximum input rating of the AD converter 6, the maximum input rating cannot be increased so much due to low power consumption and high speed of the AD converter 6. The value is not large. For this reason, X-ray acquisition efficiency falls.

  The subject of this invention is providing the X-ray detector which can improve the radiation noise tolerance and the tolerance with respect to an external fluctuation magnetic field.

In order to solve the above problems, an X-ray detector according to the present invention amplifies the X-ray detected by the X-ray sensor and the X-ray detected by the X-ray sensor, and the peak value of one step is incident X A preamplifier for outputting a staircase wave corresponding to the energy of the line; an AD converter for converting the signal amplified by the preamplifier into a digital signal; and a digital signal converted by the AD converter as a differential signal A digital processing circuit for converting to and outputting the signal, and the AD converter and the digital processing circuit are mounted on the same substrate as the substrate of the preamplifier, and noise from the AD converter and the digital processing circuit A differential receiver that differentially amplifies the output signal of the preamplifier and outputs a differential amplified signal, and a low frequency of the differential amplified signal from the differential receiver Through A first low-pass filter which is characterized in that a second low-pass filter which passes low frequency signals from the digital processing circuit.

According to the present invention, since a digital processing circuit is used and the output signal format is a differential type, the SGND line is not required for the conventional cable. For this reason, there is no noise path affecting the preamplifier, and the radiation noise resistance is improved. In addition, an unnecessary GND loop is eliminated between the X-ray detector and the external measurement system, and resistance to an externally varying magnetic field is improved. Also, a differential receiver for mounting an AD converter and a digital processing circuit on the same substrate as the preamplifier substrate, differentially amplifying the output signal of the preamplifier and outputting a differential amplified signal, and a differential receiver Since the first low-pass filter that passes the low-frequency of the differential amplification signal from the digital signal and the second low-pass filter that passes the low-frequency of the signal from the digital processing circuit are provided, the AD converter and the digital It is possible to prevent noise from the processing circuit from entering the preamplifier.

1 is a configuration diagram of an X-ray detector according to Embodiment 1. FIG. 2 is a configuration diagram of a clock generator in the X-ray detector according to Embodiment 1. FIG. FIG. 3 is a diagram showing a differential clock signal output from the clock generator shown in FIG. 2. It is a block diagram of the conventional X-ray detector. It is an output waveform diagram of a preamplifier in a conventional X-ray detector.

  Hereinafter, embodiments of the X-ray detector of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of the X-ray detector according to the first embodiment. The X-ray detector of Example 1 shown in FIG. 1 is used in, for example, an energy-type fluorescent X-ray analyzer, and includes an X-ray sensor 1, a preamplifier 10, a differential receiver 11, an LPF 12, a clock generator 13, and a digital It has a processing circuit 14 and filters 15A, 15a to 15d.

  The X-ray sensor 1 detects X-rays. The preamplifier 10 includes a low-noise JFET 21, a feedback capacitor 22, and an amplifier 23. The preamplifier 10 amplifies a minute analog signal from the X-ray sensor 1, and the peak value of one step corresponds to the energy of incident X-rays. To output a staircase wave. The discrimination circuit 8 turns on the transistor Tr1 when the output of the preamplifier 10 exceeds a predetermined value.

  The differential receiver 11 has one input terminal connected to the output terminal of the preamplifier 10 and the other input terminal connected to SGND, and differentially amplifies the output signal of the preamplifier 10. The SGND of the differential receiver 11 is connected to the SGND of the source terminal of the JFET 21.

  The LPF 12 is a low-pass filter that passes a low-frequency, and low-pass filters the differential signal from the differential receiver 11. The clock generator 13 generates differential clock signals that are 180 ° out of phase with each other, and outputs the differential clock signals to the AD converter 6 via the filter 15A as a sampling clock.

  The AD converter 6 converts the signal differentially amplified by the differential receiver 11 via the LPF 12 with a sampling clock from the clock generator 13 to convert it into a digital signal. The digital processing circuit 14 converts the digital signal converted by the AD converter 6 into a differential signal and serially transmits the differential signal via the filters 15a to 15d.

FIG. 2 is a configuration diagram of a clock generator in the X-ray detector according to the first embodiment. In the clock generator 13 shown in FIG. 2, the gate of the transistor Q1 and the gate of the transistor Q2 are connected via a diode, the input terminal IN1 is connected to this connection point, and the emitter of the transistor Q1 and the emitter of the transistor Q2 are connected. The output terminal CLK1 is connected to this connection point. (Because the transistor does not operate ON / OFF without a diode)
The gate of the transistor Q3 and the gate of the transistor Q4 are connected via a diode, the input terminal IN2 is connected to this connection point, the emitter of the transistor Q3 and the emitter of the transistor Q4 are connected, and the output terminal CLK2 is connected to this connection point. Is connected. When an on / off signal is alternately input to the input terminal IN1 and the input terminal IN2, differential clock signals having a phase difference of 180 ° are output to the output terminal CLK1 and the output terminal CLK2.

  According to the X-ray detector of the first embodiment configured as described above, the minute signal detected by the X-ray sensor 1 is amplified by the preamplifier 10. The amplified signal is converted into a digital signal by the AD converter 6 via the differential receiver 11 and the LPF 12. The converted digital signal is converted into a differential signal by the digital processing circuit 14 and serially transmitted to the outside.

  That is, since the digital processing circuit 14 is used and the output signal format is a differential type, the conventional cable 4 does not require the SGND line. For this reason, there is no noise path affecting the preamplifier 10, and radiation noise resistance is improved. In addition, an unnecessary GND loop is eliminated between the X-ray detector and the external measurement system, and resistance to an externally varying magnetic field is improved.

  Since the discrimination circuit 8, the preamplifier 10, the differential receiver 11, the LPF 12, the clock generator 13, the AD converter 6, the digital processing circuit 14, and the filters 15A and 15a to 15d are shielded by the shield unit 16, Intrusion of external radiation noise can be prevented.

  Further, as the output format is digitized, the AD converter 6 and the digital processing circuit 14 are mounted on the same substrate as the substrate of the preamplifier 10, so that noise is generated from each noise source of the AD converter 6 and the digital processing circuit 14. There is a risk that the preamplifier 10 will be squeezed and the performance such as resolution will deteriorate.

  For this reason, in order to prevent sneaking from each noise source to the preamplifier 10, the differential receiver 11, the LPF 12, the clock generator 13, and the filters 15a to 15d are provided in the first embodiment.

  The differential receiver 11 functions as a buffer between the AD converter 6 and the preamplifier 10, prevents backflow of noise generated in the AD converter 6 to the preamplifier 10, and reduces common mode noise. Remove. Thereby, it is possible to reduce the influence that noise generated in the AD converter 6 and the digital processing circuit 14 becomes internal noise of the preamplifier 10 from SGND via the JFET 21.

Since the clock generator 13 uses a differential output type that outputs a differential clock signal, noise generated in the AD converter 6 can be reduced. Further, since the LPF 12 is provided at the input portion of the AD converter 6, it is possible to prevent the backflow of noise generated in the AD converter 6 to the preamplifier 10.
Further, since the filters 15a to 15d such as coils are provided on the output side of the digital processing circuit 14, radiation noise generated in the output signal line can be reduced. Thereby, the wrapping of the radiation noise to the preamplifier 10 can be suppressed.

Further, the waveform shaping time τ of the X-ray detector is a time slightly longer than the time required from the minimum value to the maximum value of the peak value wh of one step shown in FIG. .1 μs or more. In order to cover this waveform shaping time, the bandwidth of the X-ray signal output from the preamplifier 10 is W = (2πτ) ⁻¹ to 1.6 MHz or more. For this reason, the product (GB product) of the gain G and the bandwidth B of the signal of the differential receiver 11 is 1.6 MHz or more. Further, the differential clock signal as the sampling clock of the clock generator 13 uses a frequency of 3.2 MHz or more from the Nyquist sampling theorem.

  The X-ray detector according to the present invention can be used for an energy dispersive X-ray fluorescence analyzer and the like.

1 X-ray sensor 2,10 Preamplifier
4 Cable
5 Differential Amplifier 6 AD Converter 7, 16 Shield Part 8 Discrimination Circuit 9 AD Conversion Board 11 Differential Receiver 12 LPF
13 Clock generator 14 Digital processing circuit 15A, 15a-15d Filter 18 Ground line 21 JFET
22 Feedback capacitor 23 Amplifier

Claims (4)

An X-ray sensor for detecting X-rays;
A preamplifier for amplifying the X-ray detected by the X-ray sensor and outputting a step wave whose peak value in one step corresponds to the energy of the incident X-ray;
An AD converter for converting the signal amplified by the preamplifier into a digital signal;
A digital processing circuit for converting the digital signal converted by the AD converter into a differential signal and outputting the differential signal;
Equipped with a,
The AD converter and the digital processing circuit are mounted on the same substrate as the substrate of the preamplifier, so that noise from the AD converter and the digital processing circuit does not enter the preamplifier. A differential receiver that differentially amplifies the output signal of the preamplifier and outputs a differential amplified signal; a first low-pass filter that passes a low-frequency of the differential amplified signal from the differential receiver; and the digital An X-ray detector comprising a second low-pass filter that passes a low-frequency of a signal from a processing circuit . 2. The X-ray detector according to claim 1, further comprising a clock generator that generates differential clock signals having phases different from each other by 180 ° and outputs the differential clock signals to the AD converter as sampling clocks. . 3. The X-ray detector according to claim 1, wherein a product of a gain G and a bandwidth B is 1.6 MHz or more in the differential receiver. 4. The X-ray detector according to claim 2, wherein an oscillation frequency of the differential clock signal of the clock generator is 3.2 MHz or more.

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