JPH055227B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for driving a solid-state imaging device and a method for reading out signals that reduce low-frequency noise.

[Prior art]

FIG. 1 is a diagram showing the principle of a conventional CCD type solid-state imaging device. A photosensitive section 9 consisting of photodiodes 2 arranged in a matrix, and a vertical CD 11 for reading out optical signals accumulated in the photodiodes.
It consists of a 1N and horizontal CCD 3 and an output AMP 4 that amplifies and outputs the transferred signal.

FIG. 2 is a circuit example of the output AMP4. 30 is a small capacitance Q ₀ that converts the signal charge Q _S transferred by the horizontal CCD 3 into a voltage amount, and 31 is a capacitor
Signal voltage generated between C ₀ and proportional to signal charge Q _S
A source-follower MOS type FET outputs V ₀ =Q _S /C ₀ with low impedance, and 32 is a reset MOS type FET for removing the signal charge amount Q _S in the capacitor C ₀ to the outside.

In the device having the structure shown in FIGS. 1 and 2, signals are read out in the following manner. In other words, first 1
The signal charges accumulated in the photodiode 2 during the frame period are transferred to the vertical CCDs 11 to 11 during the vertical retrace period.
Move within 1N. The vertical CCD transfers one line per horizontal retrace period, and the signal charge is transferred to the horizontal direction.
Transfer to CCD3 sequentially. horizontal retrace period
The signal charge transferred to the CCD is sequentially transferred into the capacitor _C0 by applying a clock pulse to the horizontal CCD during one subsequent horizontal period. l
The signal charge Q ^(l) _S transferred to the capacitor C ₀ by the second clock pulse generates a voltage V ^(l) ₀ across the capacitor C ₀ , and a signal pulse with voltage amplitude V ^(l) ₀ is generated from the source follower output terminal 33. 3. Output 4l. After this, the signal charge Q ^(l) _S is removed to the outside through the reset MOS FET.
Also, at the next l+1-th clock pulse, the next signal charge Q ^(l+1) _S is transferred to the capacitor C ₀ again, and a signal pulse ^(l+1) of FIG. 3 with voltage amplitude V (l+1) ₀ is output. Thereafter, by repeating the same operation, signals are sequentially output as a signal pulse train (c) in FIG. 3 having a voltage amplitude V ^(l) ₀ proportional to the signal charge Q ^(l) _S.

FIG. 4 is an explanatory diagram of the frequency distribution of the output signal pulse train of FIG. 3c. In other words, a train of signal charges that modulates the amplitude of the output signal pulse train...Q ^(l) _S (t _l-1 ), Q ^(l) _S
(t _l ), Q ^(l+1) _S (t _l+1 ),...When the frequency distribution has the distribution shown in Figure 4 a, the frequency distribution of the output signal pulse train in Figure 3 c is as shown in Figure 4 b. It will look like this. In the figure, reference numeral 50 denotes a baseband component, which represents a frequency distribution obtained by multiplying the modulated signal in FIG. 4a by the frequency characteristic sinπfτ/πf (where τ=pulse width) resulting from pulse amplitude modulation. Further, 51 is a fundamental wave component, which consists of a carrier wave having the same frequency _fr as the reset pulse and its sidebands. Below, 5m is the m-th harmonic component of Fig. 3c, which consists of a carrier wave of frequency m×f _r and its sideband waves.

FIG. 5 shows an example of the circuit configuration of a circuit for extracting a video signal (modulated signal component) from the output signal pulse train of FIG. 3c. The output signal pulse train c of the solid-state imaging device 7 in FIG. 3 is first passed through the LPF 61.
As a result, only the baseband component (b50 in FIG. 4) of the output signal pulse train is extracted, and the signal processing circuit 62 inserts SYNC and other synchronizing signals of the television signal, and outputs it as a television signal. In the figure, 63 is a drive circuit for the solid-state imaging device. Note that the level of the baseband component 50 of the output signal pulse train extracted by the above method is determined by the width τ of the output signal pulse (capacitance C ₀
It increases in proportion to the amount of time the signal charge is held within the current. Therefore, in the signal readout method shown in FIG. 5, it is desirable to make the pulse width .tau. as wide as possible and adjust it so that it is approximately equal to the reset pulse synchronization T.

By the way, in solid-state imaging devices, the first stage transistor 31 of the output AMP 1 in FIG. 4 is generally a MOS type transistor.
Consists of FETs. The random noise of the type of AMP that applies the voltage across the capacitor C ₀ to the gate terminal of the first stage transistor as shown in Figure 2 is mainly composed of thermal noise and 1/f noise. FIG. 6 shows the above-mentioned noise components superimposed on the frequency distribution of the output signal pulse train shown in FIG. 4, where 60 indicates 1/f noise and 64 indicates thermal noise. As is clear from Figure 6, while the frequency distribution of thermal noise is flat, 1/f noise is larger as the frequency component becomes lower, and as the noise appears in a horizontal line on the screen, it significantly deteriorates the picture chamber. There is. This 1/f noise is particularly large in MOS FETs, and its influence is significant.

[Purpose of the invention]

An object of the present invention is to provide a method for driving a solid-state imaging device and a method for reading out a signal in the solid-state imaging device shown in FIG. be.

[Summary of the invention]

To achieve the above object, the present invention first provides a pulse width τ (capacitance C ₀
setting the time period for which the signal charge Q _S is held within the period T to be half of the reset pulse period T ≈T/2;
Second, the video signal is extracted by synchronous detection from the fundamental wave component of the output pulse train under the above settings. Third, the local signal used for the synchronous detection is generated by adjusting the phase of the fundamental wave of the reset pulse to generate the output signal pulse train. The feature is that a carrier wave having the same phase as the fundamental wave component is used.

In general, when the amplitude V ^(l) ₀ of the output signal pulse train in Fig. 3c changes depending on the amount of signal charge Q ^(l) _S = kcos (Pt _l ) (1) where t _l = n × T, Figure 3c
The output signal pulse train is V ₀ (t)=1/T [const+2/PsinPτ/2×kcosPt+2
_∞ 〓 ^m=1 {2/mω _R sinmω _R /2×cosmω _R t +2/mω _R −Psin(mω _R −P)τ/2×k/2cos(
mω _R −P)t+2/mω _R +Psin(mω _R +P)τ/2×
k/2cos(mω _R
+P)t}] (2) However, it can be expressed as ω _R =2πf _R =2π/T. In the above equation, the first term is the DC level,
The second term is the baseband component (Fig. 4, 50), and the third term is the baseband component (Fig. 4, 50).
The terms are the fundamental wave component and its harmonic components (Fig.
1, 52,...).

The conventional signal readout method shown in Figure 5 uses an LPF to extract the second term of equation (2).In this method, the above-mentioned term contains low frequency noise such as 1/f noise mixed in equation (2). is mixed into the read signal as is.

In the present invention, in order to prevent the mixing of low frequency noise such as 1/f noise, the high frequency region where the noise level is small, especially the fundamental wave component corresponding to the term m = 1 in the third term of equation (2), is extracted by BPF. , a video signal is extracted by synchronous detection multiplied by a local signal cosω _R t (3) created by adjusting the phase of the reset pulse fundamental wave.

In other words, the signal f(t)∝(sinτ/2(ω _R −P)/ω _R −P+sinτ/2
(ω _R +P) / ω _R +P) ×ksosPt + (term above frequency 3/4πω _R ) The baseband component of (4) (first term of equation (4)) is extracted by LPF and the frequency characteristic is corrected. By applying this, it is possible to obtain a video signal kcosPt (5) with less low frequency noise such as 1/f noise.

At this time, as is clear from the first term of equation (4), the magnitude of the detected signal changes depending on the width τ of the output signal pulse shown in FIG. 3c. In particular, the magnitude of the detection signal at P~0, which determines the SN with respect to low frequency noise, changes in proportion to |sinω _R /2τ/ω _R |. Therefore, when |sinω _R /2τ/ω _R | takes the maximum value, that is, by setting the hold time of the output signal to τ≒T/2 (6), a video signal with the best SN can be obtained. .

As described above, in the method for driving a solid-state imaging device and the method for reading signals according to the present invention,
A stable video signal with high SN and low frequency noise such as 1/f noise can be obtained.

Although the case where the signal is extracted from the fundamental component has been described above, it is generally possible to read the signal from the m-th harmonic component in a similar manner. However, at this time, by setting the width τ of the output signal pulse in Figure 3c to τ≒2n+1/2m×T (7) where n=0, 1,..., m-1, a high SN signal can be read out. be able to.

[Embodiments of the invention]

FIGS. 7 and 8 show an embodiment of a signal readout method and a driving method for realizing the method of the present invention. In FIG. 7, the solid-state imaging device 7 is driven at a clock frequency of 7.16MHz. In addition, as shown in FIG. 8, the width of the reset pulse φ _R is set to less than 70 msec, which is half of the reset pulse period T = 140 nsec, and the rising position of the signal transfer pulse φ _H2 is set approximately at the center of the rising position of the reset pulse. The width τ of the output signal pulse (the time for holding the signal charge in the capacitor _C0 ) is set to be approximately half the reset pulse period T. The output signal pulse train is P.E.
After extracting the fundamental wave component through the BPF 71 of 3.58MHz to 10.74MHz and detecting it by the synchronous detection circuit 72, the signal processing circuit 62 corrects the frequency characteristics and inserts a synchronization signal of the TV signal to generate the TV signal. Output. On the other hand, the local signal used in the synchronous detection circuit 72 uses a reset pulse φ _R and a signal transfer pulse φ _H2 synchronized with this, and a pulse (d in FIG. 7) having the same phase as the output signal pulse train is generated by the multistable multivibrator 73. After the fundamental wave is extracted by the BPF 74, the phase is finely adjusted in the detection circuit 72, and then used.

The video signal is extracted from the fundamental wave component band where there is little low frequency noise such as 1/f noise mixed in the output signal, and the width τ of the output signal pulse is reset so that the level of the fundamental wave component is maximized. Since it is set to about half of T, τ≈T/2, it is possible to obtain a video signal with little low frequency noise and a high SN ratio. Furthermore, since the detection of the video signal from the fundamental wave component is performed using a local signal generated from a reset pulse completely synchronized with the output signal pulse train, synchronous detection is performed, so that stable video signal detection can be performed.

The above has been explained using the example of the output AMP circuit shown in Fig. 2, but the output AMP circuit, such as the output AMP circuit shown in Fig. 9, generally has a type of output AMP circuit that amplifies the power or voltage of the signal voltage appearing between the AMP input terminal capacitance _C0 .
A CCD type solid-state image sensor or a device like the one shown in Figure 10.
It can also be used to read signals from solid-state imaging devices that combine MOS and CCD types, CCD line sensors, CCD delay lines, etc.

〔Effect of the invention〕

According to the present invention, in a solid-state imaging device having a type of output AMP that amplifies the power or voltage of a signal voltage appearing between the input end capacitance _C0 of a CCD type equal output AMP, a signal with less low frequency noise such as 1/f noise can be used. can be obtained.

[Brief explanation of the drawing]

Figure 1 shows the principle of a conventional CCD solid-state imaging device.
Figure 2 shows an example of the output AMP circuit, Figure 3 shows the output signal waveform, Figures 4 and 6 show the frequency distribution of the output signal in Figure 3, and Figure 5 shows the configuration of a conventional signal readout and signal processing circuit. FIG. 7 shows an example of a signal readout circuit and a signal processing circuit according to the present invention, FIG. 8 shows a method for driving a solid-state imaging device and a signal processing circuit according to the present invention, and FIG.
The figure shows an example of an output AMP circuit other than that shown in FIG. 2, and FIG. 10 is a principle diagram of a solid-state imaging device other than a CCD type to which the present invention can be applied.

Claims (1)

[Claims] 1. A signal charge Q _S sent in a pulsed manner in response to a signal transfer pulse with a predetermined period T is accumulated in the AMP input end capacitance C ₀ and appears between the capacitance C ₀ an output AMP circuit that power amplifies or voltage amplifies a signal voltage and outputs it; a detection circuit that extracts and detects a signal component from m-th harmonic components including a fundamental wave component of an output signal pulse train from the output AMP circuit; In a signal readout method for a solid-state device having a drive circuit for driving an output AMP circuit and the detection circuit, the drive circuit sets the width τ of the output signal pulse output from the output AMP circuit to τ≒2n+1/ 2m×T (where m = 1, 2, ..., n = m-1, T = reset pulse period), and the output signal is the same as the output signal generated from the above reset pulse and the above signal transfer pulse. A signal readout method for a solid-state device, characterized in that the detection circuit is driven according to pulses having the same phase and pulse width τ.