A kind of pole low light signals detection device and method
The invention belongs to optical signal detection field, is related to a kind of pole low light signals detection device and method, more particularly to it is a kind of
High accuracy pole low light signals detection device and method based on digital signal processor (DSP).
Usually occur ambient noise or interference very big in the measurement of pole low light signals and measured signal is very faint, even
Situation about being fallen into oblivion by noise.In this case, low light signals are converted into by ultra-weak electronic signal by photodetector, then by low
Noise preamps are that measured signal cannot be extracted and recovered from noise to the conventional method that ultra-weak electronic signal is amplified
's.At present conventional method is that the detection and extraction to pole low light signals is realized by lock-in amplifier or Sampling Integral device.
Lock-in amplifier utilizes noise characteristic uncorrelated to the frequency of signal and phase place, by compressed detected bandwidth chahnel reality
The significantly suppression to noise is showed, so as to improve the signal to noise ratio of signal.Sampling Integral device is to repeat frequency with signal using one
The consistent reference signal of rate, to being sampled process containing noisy signal, extracts through sampling is repeated several times, and makes the system of noise
Meter averagely goes to zero, and realizes the extraction to signal.
Both approaches have the shortcomings that the following aspects when actually used：
1) when being detected to low light signals using lock-in amplifier, need to hold before the detectors and install a chopper additional.
The effect of chopper be by incident optical signal be modulated into sinusoidal ac signal and export one with modulated signal with frequency homophase ginseng
Signal is examined to lock-in amplifier.This proposes very high requirement to chopper, and optical signal can be modulated in time domain sine
Signal, and the reference signal and the modulated signal that export are with frequency homophase, also require reference signal possess very high frequency stability with
Exempt to drift out beyond arrowband.Generally, a chopper that can meet above-mentioned requirements is sufficiently expensive, increased development task cost.
2) due to the equipment that lock-in amplifier and chopper are two autonomous workings, reference signal is passing through cable transmission extremely
The phase shift of signal may be caused during lock-in amplifier reference edge because of the impact of cable distributed constant.In addition, reference signal exists
If being subject to electromagnetic interference in transmitting procedure, its frequency and phase place can disturbed signal modulations.This can undoubtedly cause final test
Inaccurate, particularly in long range propagation or poor electromagnetic environment, these affect clearly.
3) Sampling Integral device is a kind of instrument of cycle repeating signal faint in measurement noise, therefore in the measurement pole low light level
Need also exist for during signal to periodically being modulated by light-metering, and lock-in amplifier there is a problem of it is similar.
4) core of Sampling Integral device is sampling simulation switch and RC integrating circuit, and wherein sampling simulation is switched in gate pulse
Control under by carrying out interval sampling to faint analog signal, and RC integrating circuit are right in the time connected in analog switch
The analog signal values of sampling are integrated, then export Jing after final stage is amplified.Analog switch belongs to semiconductor devices, there is electric leakage
Stream, can not realize shut-off truly, can introduce extra noise.RC integrating circuit determine integration time constant τ,
What the capacitance of generally electric capacity C was to determine, just realize the regulation to τ by adjusting the resistance of resistance R, but due to R resistance simultaneously
Can not accurately be measured, therefore accurate adjustment can not be realized to integration time constant τ.
5) after lock-in amplifier and Sampling Integral device are required to amplify detector output signal Jing road of discharging before low noise
Extremely weak useful signal is extracted again.Usually require that detector output and preamplifier input close proximity to and to the greatest extent
Amount shortens preamplifier output and the transmission range between lock-in amplifier or Sampling Integral device input.On the one hand, can subtract
Few signal attenuation, on the other hand can reduce long range propagation and be disturbed by external electromagnetic environment.But can so limit one
The application of a little special occasions, particularly when detector riding position away from preamplifier farther out when or preamplifier away from tester
Device farther out when, signal attenuation and the interference of external electromagnetic environment can have a strong impact on test result.
6) generally when using lock-in amplifier or Sampling Integral device, tend not to determine signal preamplifier itself
Noise, it is uncorrelated to measured signal because this partial noise is not over modulation, belong to the background noise of circuit.
The content of the invention
Not enough and limitation in order to solve technical background existing for common method, the present invention proposes a kind of cost
It is low, simple to operate, the pole low light signals detection device and method that carry out accurately detecting to pole low light signals can be realized.
The present invention concrete technical scheme be：
A kind of pole low light signals detection device, it is characterised in that：Including mechanical shutter, photomultiplier, low noise is preposition
Amplifier, high-pass filtering circuit, high resolution A/D change-over circuits, DSP process circuits, fast gate drive circuit and computer；
Photomultiplier and enter to be provided with mechanical shutter between the emitter-base bandgap grading low light level, before the output end of photomultiplier and low noise
The input connection of amplifier is put, the output end of low-noise preamplifier is connected with the input of high-pass filtering circuit, high pass
The output end of filter circuit is connected with the input of high resolution A/D change-over circuits, the output end of high resolution A/D change-over circuits
It is connected with the input of DSP process circuits, DSP process circuits are connected with each other with computer；The mechanical shutter and DSP process electricity
Fast gate drive circuit is provided between road.
Above-mentioned low-noise preamplifier turns voltage-type preamplifier for low current；The low-noise preamplifier
Bias current is less than 2pA, 106Noise≤2mV during I/V conversion gainsp-p；；The high-pass filtering circuit is filtered to meet and filtered
Low-frequency component less than 100Hz；The resolution scale of the high resolution A/D change-over circuits is 16bit.
It is connected with each other by shield type netting twine between above computer and DSP process circuits.
According to above-mentioned detection device, it is proposed that a detection method of the device, it is characterised in that comprise the following steps：
1) parameters such as modulation period on computers to pole low light signals, sampling time, sampling interval and sampling number
2) computer is by step 1) parameter of setting transmitted to DSP process circuits；
3) DSP process circuits control fast gate drive circuit and make mechanical shutter to pole low light signals according to the modulation period of setting
It is modulated；
4) photomultiplier is detected and is exported low current signal to the pole low light signals after modulation；
5) (bias current is less than 2pA to low noise pre-amplification circuit, 106Noise≤2mV when I/V is changedp-p；) receive
Photomultiplier output low current signal is converted into voltage signal and amplifies, and then exports the voltage signal of the amplification；
6) high-pass filtering circuit receives the voltage signal of amplification and carries out high-pass filtering to the signal, filters below 100Hz
Low-frequency component, then by after filtration voltage signal export；
7) voltage signal after high resolution A/D change-over circuits accept filter is converted into 16bit data signals and believes this
Number transmit to DSP process circuits；
8) DSP process circuits are acquired to data signal, go background noise, digital sampling, bandpass filtering and numeral product
Get the signal data of the most ultimate low light level, then computer is sent data to by shield type netting twine；
Wherein, it is described to remove background noise to remove low noise pre-amplification circuit noise.
Above-mentioned steps 8) in it is as follows the step of removing background noise：
8.1) mechanical shutter is closed, without optical signal input；
8.2) weak voltage signals of body are amplified and are exported to high-pass filtering circuit by low noise pre-amplification circuit；Put
Weak voltage signals Jing high-pass filtering circuits after big filter low-frequency component, and the voltage signal after filtration is transmitted to high-resolution
A/D change-over circuits；Voltage signal after filtration is converted into data signal and by the data signal by high resolution A/D change-over circuits
Transmit to DSP process circuits；
8.3) data record when DSP process circuits close mechanical shutter is the background noise of pre-amplification circuit；
8.4) data signal when having optical signal incident is deducted DSP process circuits the background noise of pre-amplification circuit.
It is an advantage of the current invention that：
1st, the present invention is modulated by mechanical shutter to the incident low light level, and all working is carried out by DSP process circuits
SECO, makes between modulation circuit and Acquisition Circuit sequential relationship clearly, and with correlation, modulation system is simple and low cost
It is honest and clean；
2nd, the present invention can determine the background noise of low-noise preamplifier under mechanical shutter CLOSE states, and can
The impact of background noise is deducted by DSP process circuits, makes result truer, credible；
3rd, the present invention adopts high-resolution A/D change-over circuits, makes sampled result be more nearly actual value；
4th, the present invention carries out the determination in sampling time and sampling interval using DSP process circuits to data, it is to avoid sample
The inaccuracy that the noise and RC integrating circuit that analog switch itself is introduced brings；
5th, the present invention carries out digital filtering using high-pass filtering circuit to data, reduces and filters what is introduced by circuit hardware
6th, the present invention carries out digital integration using DSP process circuits to the data after sampling, and processing speed is fast；
7th, the DSP process circuits and computer in the present invention is connected by shield type netting twine, and output data is numeric type, is resisted
Interference performance is strong, and by shield type netting twine the data transmission distance of most long 90m is capable of achieving；
8th, cost of implementation of the present invention is low, reproducible, easy to operate, is easy to the integrated of system.
Description of the drawings
Fig. 1 is the structure diagram of the present invention.
1- mechanical shutters, 2- high voltage power supplies, 3- photomultipliers, 4- low-noise preamplifiers, 5- high-pass filtering circuits,
6- high resolution As/D change-over circuits, 7-DSP process circuits, the fast gate drive circuits of 8-, 9- computers.
The present invention proposes a kind of detection side of the detection device and the device that can pole low light signals be carried out with accurate detection
The structure of the device is described below in conjunction with Fig. 1：
The detection device include mechanical shutter 1, photomultiplier 3, low-noise preamplifier 4, high-pass filtering circuit 5,
High resolution A/D change-over circuits 6, electric 7 tunnel of DSP process, fast gate drive circuit 8 and computer 9；
Photomultiplier 3 and enter to be provided with mechanical shutter 1 between the emitter-base bandgap grading low light level, the output end and low noise of photomultiplier 3
The input connection of sound preamplifier 4, the output end of low-noise preamplifier 4 connects with the input of high-pass filtering circuit 5
Connect, the output end of high-pass filtering circuit 5 is connected with the input of high resolution A/D change-over circuits 6, high resolution A/D conversion electricity
The output end on road 6 is connected with the input of DSP process circuits 7, and DSP process circuits 7 are connected with each other with computer 9；Mechanical shutter 1
Fast gate drive circuit 8 is provided with and DSP process circuits 7 between.
Wherein, as it is known by the man skilled in the art that when using photomultiplier, it is necessary to photomultiplier 3
One high voltage power supply 2 of connection could meet its normal work.
Low-noise preamplifier 4 turns voltage-type preamplifier for low current；The biased electrical of low-noise preamplifier
Stream is less than 2pA, 106Noise≤2mV during I/V conversion gainsp-p；High-pass filtering circuit 5 is filtered to meet and filtered less than 100Hz
Low-frequency component；The resolution scale of high resolution A/D change-over circuits 6 is 16bit.
In addition, when the device works, in order to avoid external interference, by shielding between computer 9 and DSP process circuits 7
Type netting twine connects, and shield type netting twine is capable of achieving the data transmission distance of most long 90m, realizes noiseless, long range number
According to transmission.
By the above-mentioned description to apparatus structure, the specific work process of the device is to comprise the following steps：
Step 1) modulation period on computers to pole low light signals, sampling time, sampling interval and sampling number etc.
Parameter is set；
Step 2) computer is by step 1) parameter of setting transmitted to DSP process circuits；
Step 3) DSP process circuits control fast gate drive circuit according to the modulation period of setting makes mechanical shutter to the pole low light level
Signal is modulated；
Step 4) photomultiplier detected and exported low current signal to the pole low light signals after modulation；
Step 5) (bias current is less than 2pA to low noise pre-amplification circuit, 106Noise≤2mV when I/V is changedp-p) connect
Receive photomultiplier output low current signal to be converted into voltage signal and amplify, then export the voltage signal of the amplification；
Step 6) high-pass filtering circuit receive amplify voltage signal and high-pass filtering is carried out to the signal, filter low frequency into
Point, then the voltage signal after filtration is exported；(note：The high-pass filtering circuit that under normal circumstances we adopt is by below 100Hz
Low-frequency component filter out, so guarantee that sampled result is more accurate)
Step 7) high resolution A/D change-over circuits accept filter after voltage signal conversion digital signal and the signal is passed
Transport to DSP process circuits；
Step 8) DSP process circuits are acquired to data signal, go background noise, digital sampling, bandpass filtering sum
Word integration obtains the signal data of the most ultimate low light level, then sends data to computer by shield type netting twine；
Wherein, it is described to remove background noise to remove low noise pre-amplification circuit noise.
Step 8) in it is as follows the step of specifically remove background noise：
Step 8.1) mechanical shutter is closed, without optical signal input；
Step 8.2) low noise pre-amplification circuit by the weak voltage signals of body amplify and export to high-pass filtering electricity
Road；Weak voltage signals Jing high-pass filtering circuits after amplification filter low-frequency component, and the voltage signal transmission after filtration is paramount
Resolution ratio A/D change-over circuit；Voltage signal after filtration is converted into data signal and counts this by high resolution A/D change-over circuits
Word signal transmission is to DSP process circuits；
(note：The high-pass filtering circuit that under normal circumstances we adopt filters out the low-frequency component of below 100Hz, so
Guarantee that sampled result is more accurate)
Step 8.3) data record of DSP process circuits when mechanical shutter is closed make an uproar for the background of pre-amplification circuit
Step 8.4) DSP process circuits by the data signal for entering the emitter-base bandgap grading low light level for receiving deduct DSP process circuits receive
The data signal of low noise pre-amplification circuit this bulk noise for arriving.