CN103795939A - Sampling system using variable band pass filter and double- correlation sampling method - Google Patents
Sampling system using variable band pass filter and double- correlation sampling method Download PDFInfo
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- CN103795939A CN103795939A CN201410029585.XA CN201410029585A CN103795939A CN 103795939 A CN103795939 A CN 103795939A CN 201410029585 A CN201410029585 A CN 201410029585A CN 103795939 A CN103795939 A CN 103795939A
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Abstract
The invention relates to a sampling system using a variable band pass filter and a double- correlation sampling method. The method comprises the following steps: a high-frequency mode is used for clamping signals to 0V in reference voltage time, and a PLD is used for generating control and synchronous signals in a reading period; before the voltage of the control and synchronous signals come, the filter is converted into a low-frequency mode so as to enable an output step signal equal to delta V to generate an output pulse; at the time of t=tmax, the output signal of the filter is sampled and quantized, and then next pixel sequence begins again. Compared with the prior art, the double-correlation sampling method based on the variable band pass filter has the advantages of being high in stability, low in manufacture cost and capable of being connected with an A/D converter conveniently, is a beneficial attempt to restricting the output noise of a CCD, and plays a positive promoting role in improving the signal to noise ratio of output signals of the CCD.
Description
Technical field
The invention belongs to photoelectric sensing application, be specifically related to a kind of sampling system of alterable band-pass filter and two-phase of using and close the method for sampling.
Background technology
High-quality CCD image device is used in above the sense amplifier of integrated chip conventionally, but is easy to be subject to the restriction of burying noise that channel mosfet produces of sense amplifier.MOSFET produces white noise and low-frequency noise, the spectral density 1f of this low-frequency noise
xbe directly proportional, the structural approach that x depends on biasing, working temperature and uses, the scope of x is 1～2.CDS signal acquiring system is in the output signal of CCD, to extract Pixel Information, suppress additional noise.Known that Pixel Information (electric charge of the some of collecting) is reflected in by reference to the difference DELTA V of voltage and signal voltage in the output of CCD from pixel.The method of this measurement is exactly CDS, and it can remove the KTC noise producing due to reseting procedure.
Summary of the invention
The problem to be solved in the present invention is that existing two-phase is closed Sampling techniques poor stability, and cost of manufacture is high, can not accomplish high speed acquisition and effectively suppress the problem that noise develops simultaneously, and provides a kind of sampling system of alterable band-pass filter and two-phase of using to close the method for sampling.
In order to solve the problems of the technologies described above, technical scheme of the present invention is specific as follows:
Use the two-phase of alterable band-pass filter to close a method of sampling, comprise the following steps:
Step 1, within the reference voltage time, utilize high frequency HF pattern that signal is clamped to 0V, a PLD is for generation of the control between reading duration and synchronizing signal;
Step 2, controlling and the voltage of synchronizing signal is transformed into low frequency LF pattern filter before arriving, making the input step signal that equals Δ V produce an output pulse;
Step 3, at t=t
maxin the moment, the output signal of filter is sampled, quantizes, and next pixel sequence restarts subsequently.
In technique scheme, in step 3 in when sampling, the reading from the reset of CCD output stage electric capacity of pixel.
In technique scheme, the method for the measurement of the Δ V in step 2 is:
In the time that reference voltage signal is imported into filter, control band pass filter and be operated in high frequency mode, before reference voltage finishes, the output voltage of filter will be set to 0V, and the value of reference voltage is passed through capacitor C
1storage.
A sampling system that uses alterable band-pass filter, comprises successively: preamplifier, alterable band-pass filter, A/D converter, FET triode;
By control gate voltage V
gs, FET triode bias voltage, adjustable equivalent resistance R1, R2, can change the frequency response of described alterable band-pass filter.
The present invention has following beneficial effect:
The present invention is directed to the limitation that tradition suppresses noise technique, proposed sampling system based on alterable band-pass filter and two-phase and closed the method for sampling, this two-phase is closed the method for sampling and is had that stability is high, cost of manufacture is low, is convenient to and the advantage such as A/D converter is connected than existing Correlated Double Sampling.This is the Beneficial that the output noise to suppressing CCD is carried out, and will the signal to noise ratio that improve ccd output signal be played to positive facilitation.
Accompanying drawing explanation
Below in conjunction with the drawings and specific embodiments, the present invention is described in further details
Fig. 1 is that schematic diagram is analyzed in reseting procedure and sampling instant.
Fig. 2 is CCD floating grid export structure and the signal acquiring system schematic diagram based on band pass filter.
Fig. 3 is the readout sequence schematic diagram of pixel.
Embodiment
Invention thought of the present invention is:
High-quality CCD image device is used in above the sense amplifier of integrated chip conventionally, but is easy to be subject to the restriction of burying noise that channel mosfet produces of sense amplifier.
MOSFET produces white noise and low-frequency noise, the spectral density 1f of this low-frequency noise
xbe directly proportional, the structural approach that x depends on biasing, working temperature and uses, the scope of x is 1～2.CDS signal acquiring system is in the output signal of CCD, to extract Pixel Information, suppress additional noise.Known that Pixel Information (electric charge of the some of collecting) is reflected in by reference to the difference DELTA V of voltage and signal voltage in the output of CCD from pixel.The method of this measurement is exactly CDS, and it can remove the KTC noise producing due to reseting procedure.About the best solution of sensitivity depends on the matching degree between noise spectral density and the acquisition system transfer function of ccd output signal, the sampling system proposing here and two-phase are closed the method for sampling and are applicable to low noise occasion.
Use the composition of sampling system of alterable band-pass filter: sampling system by preamplifier, there are the variable band pass filter of centre frequency, A/D converter, FET triode etc. and form, by control gate voltage V
gs, triode bias voltage, adjustable equivalent resistance R1, R2, just can change the frequency response of filter.At two kinds extreme in the situation that, the saturated or insulation of FET or the degree of depth, the centre frequency of band pass filter is set to respectively maximum high frequency HF or minimum low frequency LF.
Use the two-phase of alterable band-pass filter to close the method for sampling, its basic step is by realizing below:
Within the reference voltage time, first utilize high frequency HF pattern that signal is clamped to 0V, a PLD is for generation of the control between reading duration and synchronizing signal, before signal voltage arrives, filter is transformed into low frequency LF pattern, make the input step signal that equals Δ V produce an output pulse, its peak value appears at t
maxin the moment, amplitude equals K
Δ V, the gain of the relative band pass filter of K is a constant.At t=t
maxin the moment, the output signal of filter is sampled, quantizes, and next pixel sequence restarts subsequently.
It is the utilization of the band pass filter based on variable that two-phase of the present invention is closed the method for sampling, the centre frequency of band pass filter can be transformed into low frequency LF (Low Frequency) pattern from high frequency HF (High Frequency) pattern, the change of frequency realizes by changing resistance value, and time constant has just obtained change.High frequency HF and low frequency LF pattern can allow to extract the useful signal value Δ V with lower noise bandwidth of equal value.
Below in conjunction with accompanying drawing, the present invention is described in detail.
The correlated-double-sampling moment is analyzed as shown in Figure 1.At t
5moment samples for the first time, and what obtain is not have signal to only have the voltage of reset noise, at t
6moment samples for the second time, and what obtain is the stack of signal voltage and reset noise voltage.Then voltage double sampling being obtained subtracts each other processing in circuit, just reset noise can be offset.Cancellation level will depend on the degree of correlation of the reset noise that double sampling obtains.Depend on the time interval between double sampling.In the situation that twice sample time, correlation was very strong in front and back, double sampling value is subtracted each other, just substantially suppress the reset noise in output signal, the difference of double sampling is the true composition of the useful video voltage that signal charge is corresponding.Because two-phase pass sampling method circuit is fairly simple, realize than being easier to, therefore in scientific experimentation noise reduction, often use, but found through experiments, two-phase is closed sampling method three so main deficiencies when with analog circuitry processes CCD reset noise, and the operational amplifier that the first is used in the time of sampling and filtering all can be introduced noise, and the output signal of CCD is faint voltage signal, generally at hundreds of millivolt, so the interference that the noise that these devices are introduced produces ccd signal be can not ignore.It two is sampling time of analog signal to be difficult to control, and the resistance of using and the numerical value of electric capacity are difficult to accurately, thereby RC time constant is difficult to accurately, affect sample effect.It three is can not accomplish high speed acquisition and effectively suppress noise and develop simultaneously.
High-quality CCD image device is used in above the sense amplifier of integrated chip conventionally, but is easy to be subject to the restriction of burying noise that channel mosfet produces of sense amplifier.
MOSFET produces white noise and low-frequency noise, the spectral density 1f of this low-frequency noise
xbe directly proportional, the structural approach that x depends on biasing, working temperature and uses, the scope of x is 1～2.CDS signal acquiring system is in the output signal of CCD, to extract Pixel Information, suppress additional noise.Known that Pixel Information (electric charge of the some of collecting) is reflected in by reference to the difference DELTA V of voltage and signal voltage in the output of CCD from pixel.The method of this measurement is exactly CDS, and it can remove the KTC noise producing due to reseting procedure.About the best solution of sensitivity depends on the matching degree between noise spectral density and the acquisition system transfer function of ccd output signal, two correlation techniques that the present invention proposes are applicable to low noise occasion.
Use the sampling system of alterable band-pass filter as shown in Figure 2, use alterable band-pass filter two-phase to close clock waveform that sampling method is relevant as shown in Figure 3.
Sampling system by preamplifier, there are the variable band pass filter of centre frequency, A/D converter, FET triode etc. and form, by control gate voltage V
gs, triode bias voltage, adjustable equivalent resistance R1, R2, just can change the frequency response of filter.At two kinds extreme in the situation that, the saturated or insulation of FET or the degree of depth, the centre frequency of band pass filter is set to respectively maximum high frequency HF or minimum low frequency LF.
It is the utilization of the band pass filter based on variable that two-phase is closed the method for sampling, the centre frequency of band pass filter can be transformed into low frequency LF (Low Frequency) pattern from high frequency HF (High Frequency) pattern, the change of frequency realizes by changing resistance value, and time constant has just obtained change.High frequency HF and low frequency LF pattern can allow to extract the useful signal value Δ V with lower noise bandwidth of equal value, basic skills is: within the reference voltage time, first utilize high frequency HF pattern that signal is clamped to 0V, a PLD is for generation of the control between reading duration and synchronizing signal, before signal voltage arrives, filter is transformed into low frequency LF pattern, make the input step signal that equals Δ V produce an output pulse, its peak value appears at t
maxin the moment (referring to Fig. 3), amplitude equals K
Δ V, the gain of the relative band pass filter of K is a constant.At t=t
maxin the moment, the output signal of filter is sampled, quantizes, and next pixel sequence restarts subsequently, has provided the type signal response schematic diagram of a pixel in Fig. 3.
As previously mentioned, cause three kinds of different magnitudes of voltage thereby the ccd output signal in pixel is read period has experienced three phases, the duration of these magnitudes of voltage provides in the drawings.Reading of pixel is from the reset of CCD output stage electric capacity, removes the electric charge of previous pixel with this.Then reset transistor becomes OFF, will cause like this output voltage to decline, and this is because parasitic capacitance coupling between clock input and CCD output stage causes.
Output signal must be carried out record by acquisition system corresponding to reference voltage, and this is because the decline Δ V of voltage subsequently follows O while shifting
l2change.In the decline of electric charge and pixel, the quantity of electric charge is proportional.The Δ V method of measuring is in the time that reference voltage signal is imported into filter, to control band pass filter to be operated in high frequency HF pattern, because the centre frequency of this pattern is higher, before reference voltage finishes, the output voltage of filter will be set to 0V, and the value of reference voltage is passed through capacitor C
1storage.The time constant that it is emphasized that band pass filter in high frequency HF pattern at this is little compared with reference voltage duration, allows reference voltage to regard constant value signal as here.Therefore, the output of filter becomes 0V very soon, and just keeps this value as long as output does not change.In the ending phase of reference voltage, by normal R of increase time
1c
1and R
2c
2, filter becomes low frequency mode, and this is the gate voltage by reducing FET triode, increases that channel resistance completes, and filter is to realize by way as follows now: the step input that equals Δ V produces a pulse, and the peak value of pulse appears at T
3+ t
maxplace.Now, the output signal of filter is sampled and quantizes, and the value obtaining is directly proportional to Δ V.
Obviously, above-described embodiment is only for example is clearly described, and the not restriction to execution mode.For those of ordinary skill in the field, can also make other changes in different forms on the basis of the above description.Here without also giving exhaustive to all execution modes.And the apparent variation of being extended out thus or variation are still among the protection range in the invention.
Claims (4)
1. use the two-phase of alterable band-pass filter to close a method of sampling, it is characterized in that, comprise the following steps:
Step 1, within the reference voltage time, utilize high frequency HF pattern that signal is clamped to 0V, a PLD is for generation of the control between reading duration and synchronizing signal;
Step 2, controlling and the voltage of synchronizing signal is transformed into low frequency LF pattern filter before arriving, making the input step signal that equals Δ V produce an output pulse;
Step 3, at t=t
maxin the moment, the output signal of filter is sampled, quantizes, and next pixel sequence restarts subsequently.
2. two-phase according to claim 1 is closed the method for sampling, it is characterized in that, in step 3 in the time of sampling, the reading from the reset of CCD output stage electric capacity of pixel.
3. two-phase according to claim 1 is closed the method for sampling, it is characterized in that, the method for the measurement of the Δ V in step 2 is:
In the time that reference voltage signal is imported into filter, control band pass filter and be operated in high frequency mode, before reference voltage finishes, the output voltage of filter will be set to 0V, and the value of reference voltage is passed through capacitor C
1storage.
4. a sampling system that uses alterable band-pass filter, is characterized in that, comprises successively: preamplifier, alterable band-pass filter, A/D converter, FET triode;
By control gate voltage V
gs, FET triode bias voltage, adjustable equivalent resistance R1, R2, can change the frequency response of described alterable band-pass filter.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107079123A (en) * | 2014-10-06 | 2017-08-18 | 索尼半导体解决方案公司 | Signal processing apparatus, signal processing method, photographing element and electronic equipment |
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| CN101262209A (en) * | 2007-03-09 | 2008-09-10 | 阿尔卑斯电气株式会社 | Alterable band-pass filter |
| CN202340206U (en) * | 2011-10-25 | 2012-07-18 | 汉王科技股份有限公司 | Electromagnetic induction device with variable band-pass filter |
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2014
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101262209A (en) * | 2007-03-09 | 2008-09-10 | 阿尔卑斯电气株式会社 | Alterable band-pass filter |
| CN202340206U (en) * | 2011-10-25 | 2012-07-18 | 汉王科技股份有限公司 | Electromagnetic induction device with variable band-pass filter |
Non-Patent Citations (1)
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| CN107079123A (en) * | 2014-10-06 | 2017-08-18 | 索尼半导体解决方案公司 | Signal processing apparatus, signal processing method, photographing element and electronic equipment |
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Application publication date: 20140514 |