GB/T 4079-1994 Test methods for amplifiers and charge sensitive preamplifiers for ionizing radiation detectors
Some standard content:
UDC539.1.074：621.039.5
National Standard of the People's Republic of China
GB/T4079—94
Test procedures for amplifiers and charge-sensitivepreamplifiers used with detectors of ionizing radiationPromulgated on December 22, 1994
State Administration of Technical Supervision
Implementation on October 1, 1995
Subject content and scope of application
Referenced standards
Terms, symbols, codes
Test instrument
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Measurement methods for the main parameters of the main amplifier 5
Test methods for the main parameters of the preamplifier
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（6）
（13）
Method".
National Standard of the People's Republic of China
Test procedures for amplifiers and charge-sensitive preamplifiers used with detectors of ionizing radiation GB/T4079—94
Replaces GB4079—83
This standard adopts IEC1151 Nuclear Instruments—Test procedures for amplifiers and preamplifiers used with detectors of ionizing radiation 1 Subject content and scope of application
This standard specifies the test methods for main amplifiers (shaping amplifiers) and charge-sensitive preamplifiers used with detectors of ionizing radiation. This standard applies to main amplifiers and charge-sensitive preamplifiers used with semiconductor detectors, gas pulse ionization chambers, and proportional detectors, and also to main amplifiers used with scintillation detectors. 2 Reference standards
GB5962 Standard nuclear instrument plug-in
3 Terms, symbols, codes
3.1 Terms
3.1.1 Preamplifier preamplifier
An electronic amplifier located between the radiation detector and the main amplifier or other electrical components and immediately connected to the output of the detector. 3.1.2 Charge-sensitive preamplifier charge-sensitive preamplier A preamplifier whose output signal is proportional to the input charge and is basically independent of the input capacitance. 3.1.3 Main amplifier (shaping amplifier) Main amplifier (shaping amplifier) In an amplifier system, an amplifier following the preamplifier and containing a pulse shaping network. 3.1.4 Charge sensitivity, charge The ratio of the output voltage of a charge-sensitive preamplifier to the input charge. It can also be defined as the ratio of the output voltage to the energy of the incident particle of a given detector.
3.1.5 Detector capacitance capacitance of detector Under a specified bias voltage, the inter-electrode capacitance of the detector. 3.1.6 Rectangular pulse rectangular pulse A flat-top pulse with a step time much shorter than the top duration. 3.1.7 Tail pulse tail pulse
A pulse with a very fast rise time and exponential decay with a time constant much longer than the rise time. 3.1.8 Differentiator differentiator
A high-pass network consisting of a capacitor and a resistor, whose output signal is proportional to the mathematical differential of the input signal. 3.1.9 Quasi-Gaussian
Approved by the State Administration of Technical Supervision on December 22, 1994 and implemented on October 1, 1995
GB/T4079-94
A signal shape that approximates a normal distribution. Unless otherwise specified, in this standard it refers to the pulse shape generated by a differentiator and four (or more) integrators.
3.1.10 Shaping network shapingnetwork A network consisting of a high-pass network (composed of one or several differentiators) and a low-pass network (composed of several integrators). It can reduce the width of the output pulse of the preamplifier, thereby improving its time resolution and signal-to-noise ratio. 3.1.11 Rise time risetime
The time required for the pulse to rise from 10% to 90% of its maximum value. 3.1.12 Peaking time (of a shaped pulse) peakingtime (of a shaped pulse) The time interval between the 1% point of the leading edge amplitude and the peak center line of a unipolar pulse. 3.1.13 Pulse width pulsewidth
The time interval between two points in a unipolar pulse waveform where the amplitude is half of the peak amplitude. It is also called the shaping time mark t/2. 3.1.14 Pole-Zero cancellation Pole-Zero cancellation uses poles and zeros to cancel each other to achieve compensation. 3.1.15 Gain of amplifier gainofanamplifier The ratio of the output pulse amplitude of the amplifier to the input pulse amplitude. 3.1.16 Equivalent input noise equivalentinputnoise In an amplifier, the output noise signal divided by the gain of the amplifier. 3.1.17 Noise transition gain noisetransitiongain A gain value in the main amplifier, below which the output noise is almost independent of the gain, and above which the output noise is almost proportional to the gain.
3.1.18 Noise line width noiselinewidth The width of the spectrum obtained by replacing the signal generated by the radiation source with a noise-free electric pulse of a certain amplitude. 3.1.19 Dynamic range dynamicrange
The range of pulse amplitudes over which the amplifier gives a linear response. 3.1.20 Integral nonlinearity integralnonlinearity The difference between the actual transfer characteristic curve and the ideal straight line within the output amplitude range, expressed as a percentage of the ratio of the maximum deviation from the linear response to the maximum rated output pulse amplitude. 3.1.21 Differential nonlinearity differentialnonlinearity In the entire dynamic range of the amplifier, the incremental gain change is usually expressed as a percentage of the reference increment. 3.1.22 Bipolar pulse bipoiarpulse
A pulse with a protrusion on each side of the baseline. 3.1.23 Baselinebaseline
The average value of the level. In the absence of repeated pulses, the pulse deviates from this average level and then returns to this average level. 3.1.24 Baselineshiftbaselineshift
The phenomenon of the baseline shifting due to the duty cycle (equal to the pulse time multiplied by the pulse repetition frequency) increasing from zero (usually this drift is opposite to the polarity of the signal).
3.1.25 Baselinerestorer A circuit that quickly restores the baseline to its previous level after the amplifier outputs a pulse (or series of pulses). 3.1.26 Offsetoffset
A DC deviation from a specified voltage (or current) level. Unless otherwise specified, the specified level is the baseline. 3.1.27 [Energy resolution of a radiation spectrometer] Energy resolution (of a radiation spectrometer) is a measure of the minimum relative difference between the energies of two particles that a radiation spectrometer can distinguish for a given energy. It is usually expressed as a percentage of the half-width at half maximum (FWHM) or the ratio of the half-width to the peak energy. 2
GB/T4079-94
3 (Resolving time in an amplifier system) resolving time in an amplifier system) 3.1.28
The minimum time interval between two consecutive pulses or ionization events that can still be distinguished. Unless otherwise specified, the resolving time is defined as to.01
3.1.29 Terminating resistor
terminating resistor
The resistor connected across the output of an amplifier or signal generator. The purpose is to eliminate signal reflections at these ends. 3.1.30 Characteristic impedance characteristic impedance The internal resistance (impedance) of a network (such as a coaxial cable or an attenuator). When terminated with a resistor of the same impedance, signal reflection can be avoided and the output signal is halved.
3.1.31 Walk
Changes in pulse height in the amplifier cause changes in zero-crossing time. 3.2 Symbols and codes
3.2.1A: Amplifier gain.
3.2.2AT: Noise conversion gain.
3.2.3ADC: Analog-to-digital converter.
3.2.4BLR: Baseline restorer.
3.2.5BW: Bandwidth, MHz.
3.2.6Ce: Test capacitor connecting pulse generator to preamplifier, pF. 3.2.7
Ceimt: Test capacitor in preamplifier, pF. 3.2.8Ca: Detector capacitance, pF.
3.2.9Cr: Feedback capacitance in charge-sensitive preamplifier, pF. 0C: Capacitance across preamplifier input to ground, pF. 3.2.10
△: change in increment.
AUbr: bridge output voltage (at zero, AUbr=0), mV. AU. : maximum deviation of the actual output characteristic curve from the ideal linear response, mV; N: center position of the spectrum peak on the multi-channel analyzer, channel. AN: FWHM value of the pulse generator peak, channel. E: energy of the particle or photon, keV or MeV. e: average energy required to form an ion pair, eV. en: (rms) root mean square noise voltage, mV. emi equivalent input noise, mV.
ene: root mean square noise voltage at the output of the main amplifier, mV. FWHM: half-maximum width, keV (or channel).
FW0.1M: tenth-maximum width, keV.
FW0.01M hundredth-maximum width, keV.
LI: integral nonlinearity.
Lp: differential nonlinearity.
CRT: cathode ray tube.
P/Z: pole/zero.
qn: RMS noise charge, VC.
qni: equivalent RMS noise charge referred to the preamplifier input, /C. 3.2.29
q: electron charge, q=1.602×10-19C. 3.2.31wwW.bzxz.Net
Ra: detector bias resistor, 2.
r. internal resistance, 2.
3.2.33R. : terminating resistor, 0.
GB/T4079-94
3.2.34Rr: feedback resistor in charge-sensitive preamplifier, a, 3.2.35S. : charge sensitivity, V/C. 3.2.36tPulse rise time, ns.
3.2.37tp: Peak time of unipolar pulse, μs. 3.2.38tp1: Peak time of bipolar pulse measured from 1% of the first half cycle peak height to the center of its peak, μs. 3.2.39tp2: Peak time of bipolar pulse measured from 1% of the first half cycle peak height to the center of the second peak, us. 3.2.40txo: Transition time of bipolar pulse, ns (or μs, or ms). 1/2: Shaping time mark. Also called the pulse width of unipolar pulse. 3.2.41
3.2.42ta: Pulse width at peak height n (here n is specified as 0.1, 0.001, etc.), ns (μs, ms). 3.2.43T: Time constant, μs.
3.2.44U,: Pulse generator output voltage amplitude, V. 3.2.45U.: Amplifier output pulse amplitude, V. 3.2.46
U: Amplifier input pulse amplitude, V.
U.: Amplifier maximum linear output pulse amplitude, V. 3.2.48Z.: Characteristic impedance.
4 Test Instruments
4.1 Test Block Diagram
The test block diagram of the general parameters of the amplifier is shown in Figure 1. AC voltmeter
Capacitor box
Pulse generator
Direct output
Preamplifier
Effect indicator
Main amplifier
Figure 1 Test block diagram
External trigger
The dotted lines in Figure 1 indicate changes in cable connections. This device can be used to measure all parameters except for the measurement of shake and nonlinearity of the preamplifier. When measuring the main amplifier, the preamplifier and capacitor box can be omitted. In this device, the plugs and sockets of the cable terminals, as well as the T-plugs, elbows, etc., must have good mechanical properties to ensure low contact resistance. The terminating resistors of the pulse generator and amplifier are usually 50α. 4.2 Pulse Generator
The open-circuit output voltage U of the pulse generator is greater than or equal to 10.0V, and the amplitude of the output pulse can be adjusted by a multi-turn potentiometer with a full scale of 1000 divisions.
GB/T4079—94
Unless otherwise specified, U is used. A dial equal to 10V and 1000 divisions. Different U or adjustment methods can only affect certain details in the measurement and will not affect the entire measurement method. The pulse generator has at least two outputs, one is a direct output and the other is an attenuated output. Each output has its own rear terminating resistor and has the same internal resistance r. (r. is 0.5Q or less), and there should also be an output for triggering the oscilloscope scan. The operating frequency of the pulse generator can be the power supply frequency or other frequencies. When working at other frequencies, the AC noise interference in the system can be checked.
4.2.1 To check the pulse generator of the preamplifier, a pulse generator with a flat-top pulse of t less than or equal to 1ns is generally used. A mercury relay tail pulse generator with t less than or equal to 5ns can also be used for all tests, but it cannot be used to check the exponential decay performance of the preamplifier. The t of the pulse generator should be consistent with the t of the detector. When checking the preamplifier used with semiconductor detectors and gas-filled detectors, the t of the pulse generator should not be greater than 1/3 of the shortest t of the detector or preamplifier system due to the change in the collection time of the detector. When checking the preamplifier used with a scintillation detector, the t of the pulse generator should be less than the t of the preamplifier. If the t of the scintillation detector is larger than the t of the preamplifier, the pulse generator should be adjusted to match the t of the scintillator. The pulse generator's fall time should be faster than the preamplifier's fall time. If the pulse generator's amplitude has been calibrated relative to the oscilloscope's sensitivity, then neither the pulse generator's amplitude nor the oscilloscope's sensitivity need to be accurate.
4.2.2 Checking the pulse generator of the main amplifier Use a rectangular pulse generator or a tail pulse generator. When checking overload or P/Z operation, a tail pulse must be used. The tail pulse can be obtained from a flat-top pulse by adding a capacitor between the pulse generator and the attenuator. 4.3 Attenuator
The attenuator can be part of the pulse generator or external. It is recommended that the attenuator's various settings match the main amplifier's gain coarse adjustment. The accuracy and stability of the attenuator depends on the stability and accuracy of the connected resistor. The error caused by the switch at each setting does not exceed 1% of the output signal at that setting. The attenuator's various settings should be calibrated by applying a DC voltage to the input, measuring its voltage value with a digital voltmeter, and then measuring its output voltage value with a digital voltmeter. 4.4 Capacitor Box
Figure 1 shows the circuit diagram of the capacitor box. The test capacitor C. is a known capacitor with an error of less than or equal to 1%. The box also contains a set of shunt capacitors switched by switches, which can fully cover the input capacitance range required by the preamplifier. C. should be shielded or isolated from the shunt capacitor switch so that changing the switch position does not affect the test capacitor C. value. The shunt capacitor should be made of low-loss insulating material, such as quartz, polystyrene or carbonate, low-loss ceramic, etc. The insulator of the switch and connector should also be a low-loss material. 4.5 Main amplifier
The main amplifier gain is usually between 2 and 3000 times, and the maximum linear output amplitude U. is 10V. If U. is not 10V, the test procedure should be slightly modified.
The main amplifier contains a shaping network to improve the signal-to-noise ratio and reduce the pulse width. In high-resolution spectrometers, pulse shaping is the most important one. The use of a unipolar pulse shaping time mark t/2 can facilitate the comparison of the energy resolution of amplifiers with different shaping networks.
When measuring the noise of the preamplifier, the main amplifier used should contain a quasi-Gaussian filter network. The t1/2 used should be indicated, and the influence of BLR on the noise measurement should be eliminated.
4.6AC voltmeter
This voltmeter should have an effective value response or a full-wave true-rms response, in which case the crest factor is not less than 4. In an amplifier with CR-(RC)\ shaping, the series noise is determined by formula (1) and the parallel noise is determined by formula (2). BW×t1/2≥3.8/8
...(1)
GB/T4079-94
BW×tv/2≥1.6/8
Where: BW-3db bandwidth of AC voltmeter, MHz; t/2-shaping time mark, μs;
8-allowable error, %. The measurement accuracy of the AC voltmeter should be better than 1%. 4.7 Oscilloscope
The oscilloscope should have DC coupled input, external trigger scanning and sufficient internal delay, and its rise time should be less than 1/3 of the shortest t to be measured. To measure the jitter, the oscilloscope should have a delayed scan, and its scanning speed should match the jitter to be measured. 4.8 Nonlinear bridge
A nonlinear bridge basically consists of two series resistors (usually 1kα each), one of which is connected to the amplifier to be tested and the other is connected to the pulse generator, see the box part of the bridge in Figure 1. If the two signals have opposite polarities and equal amplitudes, then the peak is zero (see Figure 2). When testing the main amplifier, if the amplifier is ideally linear, the zero state does not change when the pulse generator output is changed. If the amplifier has nonlinearity, the zero state will change. Gain is too high
+Gain is just right
Gain is too low
Figure 2 Bridge Balance Waveform
In order to subtract the signals at the addition point, the signal of one channel must be inverted. If the amplifier or preamplifier does not have an inversion function, an inverter must be added to one channel.
In order to prevent an oscilloscope with appropriate sensitivity from being overloaded and to reduce the overload effect of the oscilloscope, two low-capacitance high-frequency semiconductor diodes (such as Schottky barrier diodes) are connected to the addition point of the bridge (i.e. the output of the bridge) to form an overload limiter. 4.9 Pulse generator calibration of oscilloscope
When measuring gain, charge sensitivity, and noise, the output and input voltages that appear in the form of ratios in the formula do not need to be measured very accurately, but the pulse generator should be calibrated for the oscilloscope as follows: Connect the direct output of the pulse generator to the oscilloscope input; a.
Adjust the output of the pulse generator to 5.00V according to the value indicated on the dial; b.
At the scanning speed commonly used for amplifier measurement, adjust the sensitivity of the oscilloscope so that the pulse occupies five large grids on the CRT c.
(DIV).
When using a tail pulse generator, this calibration should be performed at the peak of the pulse. Each large grid of a normal oscilloscope contains five small grids (div). The reading value error at the top of the pulse is less than 0.5div. Recalibration should be performed before each measurement.
4.10 Multichannel analyzer
The multichannel analyzer basically consists of an ADC, a memory unit, and a display unit. If the spectrum shape in the ADC is distorted, it means that the multi-channel analyzer is not suitable for testing high-resolution amplifiers and preamplifiers. 6
5 Measurement method of the main parameters of the main amplifier GB/T4079--94
The main parameters of the main amplifier include pulse shaping parameters, gain, pole-zero compensation range, noise, integral nonlinearity, gain stability, overload recovery time, zero-crossing time jitter, count rate effect, etc. Usually, the preamplifier is not used when measuring the main amplifier. The signal source uses a tail pulse generator or a rectangular pulse generator. If a preamplifier is used, it is best to use a rectangular pulse generator. 5.1 Pulse shaping parameters
Figure 3 is a waveform diagram of unipolar and bipolar quasi-Gaussian pulses. The main amplifier shaping parameters are t1/2vtpl, tp2, txo, to.01, as shown in Figure 3.
5.1.1 Representation of unipolar pulse shaping time The shaping time of quasi-Gaussian unipolar pulses is represented by tv2. The unit of t1/2 is ns, us, or ms. If other pulse shaping parameters are used or the quasi-triangular unipolar pulse is expressed as 1:, it must be explained in the measurement results. CR-(RC)
Figure 3 Unipolar and bipolar pulses
5.1.2 Representation of bipolar pulse shaping time (CR)-(RC)
Add a differentiator with the same time constant as the first differentiator, so that the unipolar pulse can be transformed into a bipolar pulse, and its first half cycle is slightly wider than t/2 of the original unipolar pulse. This pulse width should be explained. 5.2 Measurement of the main parameters of pulse shaping
The measurement steps are as follows:
Disconnect BLR and measure the unipolar pulse first; adjust the P/Z potentiometer to completely eliminate the undershoot of the output pulse; adjust the pulse amplitude so that it is 5DIV on the CRT: increase the vertical sensitivity of the CRT by 10 times so that 2.5div represents 1% of the pulse amplitude. In this way, to.01 can be measured; d.
When the oscilloscope returns to its original sensitivity, t/2 and t can be measured. In order to improve the measurement accuracy, the scanning width should also be adjusted to make the measured parameters occupy at least 5DIV in the horizontal direction; the tp1, tp2, to.01 and txo of bipolar pulses can be measured in the same way. f.
5.3 Gain measurement
It is stipulated that the gain of the main amplifier is measured when the differential and integral time constants are equal. The gain of each time constant should meet the requirements, and the gain of the unipolar and bipolar output time should be equal, otherwise it must be explained. 5.3.1 The coarse gain measurement method is as follows:
a. Set the coarse gain of the main amplifier to the maximum; 7
GB/T4079—94
Use a pulse with a known amplitude to input the main amplifier, and ensure that the output of the main amplifier is not saturated; Use an oscilloscope to measure the output pulse amplitude; Calculate the gain of the main amplifier;
Repeat the above steps for each coarse gain level. After measuring each coarse gain level, all errors will be normalized relative to the maximum coarse gain level, and other coarse gain levels can also be selected for normalization. In addition, the range of coarse gain and the error of each gain level should also be stated. 5.3.2 The fine gain measurement method is as follows:
Set the coarse gain to any level;
Set the fine gain to the minimum and use an oscilloscope to measure the output amplitude of the main amplifier; b.
Change);
Set the fine gain to the maximum and use an oscilloscope to measure the output amplitude of the main amplifier. (At this time, the amplifier cannot be saturated, and other conditions are not d.
If the coverage range of the fine gain is 3:1, the output amplitude when the fine gain is maximum is three times that when the fine gain is minimum. When giving the measurement results, the accuracy of the fine gain should be stated. 5.4 Measurement of pole-zero compensation range
The maximum pole-zero cancellation range of the adjustable pole-zero cancellation network is infinite, so what needs to be measured is its lower limit. The method is as follows: a.
Adjust the P/Z compensation of the main amplifier to the maximum compensation position; set the main amplifier forming time to a certain position; use a pulse generator with an adjustable attenuation time constant to input into the main amplifier, use an oscilloscope to observe its output pulse, and change the pulse Generator decay time, find the maximum decay time of the P/Z network optimal compensation under this time constant; change the main amplifier shaping time, repeat 5.4d, f.
Compare the maximum pulse decay time of the optimal compensation found under different shaping times, and take the maximum one as the P/Z compensation lower limit of the main amplifier.
5.5 Noise measurement
5.5.1 Noise measurement under different gains
When measuring noise, AC and high-frequency interference, ground loop noise, ripple and noise caused by each power supply, and BLR in the main amplifier should not effectively affect the measurement results. And pay attention to the adjustment of P/Z. 5.5.1 .1 The measuring device is shown in Figure 1. Without using a preamplifier and a bridge, connect the output of the main amplifier to the input of the oscilloscope. 5.5.1.2 Set the gain of the main amplifier to the maximum, and ground its input through an impedance equal to the output impedance of the preamplifier (when the output impedance of the preamplifier used is unknown, the main amplifier should be grounded at the input with a 50α resistor), and measure the gain A of the main amplifier. 5.5.1.3 Use a root mean square voltmeter to measure the output noise eno of the main amplifier. 5.5.1.4 The equivalent noise converted to the input is: Pi
Where: A——main amplifier gain;
eai——equivalent noise converted to the input of the main amplifier Efficacy noise, mV; eno main amplifier output noise, mV. 5.5.1.5 Repeat the above measurement at different gain levels to measure the eai value at each gain level. The RMS voltmeter must have sufficient bandwidth, and the t/2 and gain range for measuring noise should also be stated. 5.5.2 Noise conversion gain
(3)
The curve of e relative to A obtained in 5.5.1 is shown in Figure 4. The inflection point Ar of the curve is defined as the noise conversion gain and should be stated in the measurement results.
5.6 Integral nonlinearity measurement
GB/T4079--94
Figure 4em.The calculation of integral nonlinearity relative to A is given by formula (4). AU.
×100%
Where: AU. Maximum deviation, mV;
U. Maximum linear output pulse amplitude of the amplifier, V. The characteristic curve of integral nonlinearity is shown in Figure 5.
Measure the integral nonlinearity of the main amplifier using the bridge method. (4)
5.6.1 Set the pulse generator direct output amplitude to U. (usually 10V), with the polarity opposite to the output pulse polarity of the main amplifier. If the main amplifier does not have an inverting amplifier, insert an inverting amplifier in one of its paths, AU
Figure 5 Dynamic characteristics of integral nonlinearity
5.6.2 Set the gain of the main amplifier to 50 times (close to the position that may be used to measure 1MeV rays with a germanium detector). 5.6.3 Adjust P/Z to achieve the best compensation of the output pulse. 5.6.4 Set the output DC level to zero.
5.6.5 Adjust the pulse generator's attenuation multiple and gain fine-tuning to make the bridge output zero. 5.6.6 Keeping all other conditions unchanged, continuously reduce the pulse generator's direct output amplitude from U to zero. Observe the change in bridge output voltage AUbr on the oscilloscope and find AUbr.max (AUbr.max=1/2AU.). 9
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