JPH04159880A - Noise suppression circuit for image pickup signal - Google Patents

Abstract

PURPOSE:To remove noise superimposed upon image pickup signals by providing a delay difference circuit which finds the difference between an input image pickup signal and a delayed image pickup signal obtained by delaying the input image pickup signal and a mixer circuit which outputs the difference signal of the delay difference circuit and the high-level signal component of a separately inputted prescribed reference pulse. CONSTITUTION:A delay difference circuit 2 which finds the difference between an input image pickup signal Vin and a delayed image pickup signal Vd obtained by delaying the signal Vin through a delay line 1 and a mixer circuit 3 which outputs the difference signal Vs of the delay difference circuit 2 and the high- level signal component VH of a separately inputted prescribed reference pulse pr are provided. Accordingly, such switching operations as sampling, etc., are not performed. Therefore, a sufficient noise suppression effect can be expected, since the correlative noise to the image pickup signal Vin which is widened in band due to an increase in the number of picture elements of a CCD image pickup element can be easily and surely eliminated and, at the same time, the return of noncorrelative high-frequency noise is also reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a noise suppression circuit for an imaging signal that removes noise superimposed on an imaging signal from, for example, a CCD type imaging device.

[Summary of the invention]

The present invention provides a noise suppression circuit for an image signal, including a delay difference circuit that takes a difference between an input image signal and a delayed image signal obtained by delaying the input image signal with a delay line, and a difference from the delay difference circuit. The configuration includes a mixing circuit that outputs a high-level signal component out of a predetermined reference pulse that is input separately from the signal, or the input imaging signal and the input imaging signal are delayed by a first delay line. a delay difference circuit that takes a difference from the obtained delayed imaging signal; and a first mixing circuit that outputs a high-level signal component among a predetermined reference pulse that is input separately from the difference signal from the delay difference circuit. , a second mixing circuit outputting a low-level signal component of a delayed output signal obtained by delaying the output signal from the first mixing circuit and the output signal by a second delay line. By configuring this, it is possible to easily and reliably remove noise from an image pickup signal which has become wider in band due to the increase in the number of pixels of a CCD type image pickup device.

[Conventional technology]

Generally, when reading an image signal from a CCD type image sensor, reset noise generated in a preamplifier poses a problem. As a method for removing this reset noise, the correlated double sampling (CDS) method has been widely used, and other methods such as the delay difference method have also been proposed.

In the CDS method, as shown in FIG. 5, the imaging signal V in (not shown in FIG. 6A) inputted to the input terminal φ, 7 is supplied to the first sampling and hold circuit (378 circuit) (11). , in this first 378 circuit (11), the above-mentioned imaging signal ■8. ．． Of these, a portion of each field is shown in Figure 6B.
After sampling and holding with the SHP pulse Pp and obtaining the output signal ■s shown in the sixth diagram, the output signal V
SHI' is supplied to the second 378 circuit (12) in the next stage, and an SHD pulse p having a phase shift of π from the above SHP pulse pp is supplied.
Sampling and holding are performed at d (see FIG. 6C) to obtain output signals ① and l(d) shown in FIG. 6E.

On the other hand, the imaging signals ■ and A supplied from the input terminals φ and 7 via the contact a are supplied to the third 378 circuit (13), and the SHD pulse pci outputs each signal of the imaging signal ■in. The output signal VSH shown in FIG. 6F is obtained by sampling and holding the output signal.

Then, the output signal ■, Hd from the second 378 circuit (12) and the output signal V from the third 378 circuit (13)
By taking the difference from SH, correlated reset noise (indicated by ○, ×, and △ in the figure) is canceled, resulting in a signal component (■) without reset noise. U.

The output terminal φ. It can be obtained from □.

Next, in the delay difference method, as shown in FIG.
The imaging signal V in shown in FIG. 8A inputted to 7 and
The difference between the image signal V in supplied from the input terminals φ and 7 through the contact a and the delayed image signal 4 (not shown in FIG. Then, the difference signal (2) shown in FIG. (In the figure, ○, ×.

After extracting the signal component (indicated by △) and obtaining the output signal ■9 shown in the eighth diagram, the output signal ■9 is supplied to the low-pass filter (23) and the output terminal φ. Baseband signal with less reset noise than UT ■. The goal is to obtain □.

[Problems to be Solved by the Invention] However, in the CDS method shown in FIG. 5, correlated reset noise can be removed, but uncorrelated high-frequency noise can be removed by sampling. In addition, it will be added as a range noise.
Since the impedance is high during the sampling and hold period, there is a possibility that external noise may be newly added, and there is a disadvantage that the noise removal effect is low.

In contrast, the delay difference method shown in Figure 7 does not perform sampling and holding, so there is less aliasing of uncorrelated high-frequency noise, and since a low-impedance circuit can be configured, there is less influence from external noise. Has characteristics.

However, in any of the above methods, as the number of pixels of the CCD image sensor increases and the band of the image signals ① and 7 becomes wider, the switching circuit for CDS and the switching circuit for the gate in the delay difference method will also have a higher band. This is disadvantageous in that it becomes difficult to realize correlated noise suppression.

The present invention has been made in view of the above points, and its purpose is to easily and reliably remove noise from an imaging signal that has become broadband due to the increase in the number of pixels of CCD type imaging devices. An object of the present invention is to provide a noise suppression circuit for an image pickup signal that can suppress noise.

[Means to solve the problem]

The imaging signal noise suppression circuit (A) of the present invention uses a delayed imaging signal V obtained by delaying the input imaging signal V in and the input imaging signal V 4y1 by a delay line (1).
, a delay difference circuit (2) that takes the difference between , and the delay difference circuit (
A mixing circuit (3) that outputs a high-level signal component Vi of a predetermined reference pulse pr input separately from the difference signal (2) from (3).

Further, the imaging signal noise suppression circuit (A) of the present invention provides delayed imaging obtained by delaying the input imaging signal V i h and the input first image signal V in by the first delay line (1). a delay difference circuit (2) that takes the difference from the signal ■6;
A first mixing circuit (3) that outputs a high-level signal component ■□ of a predetermined reference pulse pr that is input separately from the difference signal ■ from the delay difference circuit (2);
The output signal from the mixing circuit (3) ■□ and the output signal ■□
The low-level signal component of the delayed output signal ■lld obtained by delaying the signal ■lld by the second delay line (4)
, a second mixing circuit (5) that outputs .

[Operation] According to the configuration of the present invention described above, since switching operations such as sampling are not performed, correlated noise (reset noise, etc.) with respect to the imaging signal ■in, which has become wider in band due to the increase in the number of pixels of the CCD type image sensor. can be easily and reliably removed, and there is little aliasing of uncorrelated high-frequency noise, and a sufficient noise suppression effect can be expected.

In particular, according to the second configuration of the present invention, a two-legged effect can be expected, and the imaging signal V, , 1 due to noise suppression can be expected.
loss can be almost eliminated, and highly accurate signal processing can be performed.

[Example] Hereinafter, the present invention will be described in detail with reference to FIGS. 1 to 4.

FIG. 1 shows the image signal noise suppression circuit (
It is a block diagram showing A).

As shown in the figure, this circuit (A) receives image pickup signals (1) from a CCD type image pickup device. ．． is input to the delay difference circuit (2) having the first delay line (1), the difference signal vs from the delay difference circuit (2) is input to one input terminal φ1, and the difference signal vs from the delay difference circuit (2) is input to the other input terminal φ2. A first NAM receives a predetermined reference pulse pr to be described later and outputs a high-level signal component of the difference signal V and the reference pulse pr as an output signal ■ from an output terminal φ3.
Circuit (non-additve-mixing circuit)
(3), the output signal ■ from the first NAM circuit (3) is directly input to one input terminal φ4, and the output signal ■9 is input directly to the other input terminal φ5 from the second delay line (
4) and outputs the low level signal component of the above signal from the output terminal φ6 as an output signal vL;
) output signal from ■, the baseband signal ■. It has a low-pass filter (6) that shapes it as □.

Next, the operation of the noise suppression circuit (A) according to this example will be explained with reference to FIGS. 2 to 4. Here, Figure 2 is
FIGS. 3 and 4 are waveform diagrams showing signal processing of this circuit (A), and FIGS.
FIG. 5 is a circuit diagram showing an example of 5).

First, the image pickup signal V in shown in FIG. 2A inputted to the input terminal φ, 7 is supplied to the delay difference circuit (2), and the image pickup signal ① is inputted to the delay difference circuit (2). and input terminal φ
, 7 via the contact a.
phase adjustment using the first delay line (1) (Fig. 2A
1y of one pixel output period t in the imaging signal V i n of
By taking the difference from the delayed imaging signal (2) shown in FIG. 2B obtained by delaying the image by 2 minutes (delayed by 2 minutes), a difference signal (2) shown in FIG. 2C is obtained. After that, the difference signal ■ from the delay difference circuit (2),
is supplied to the negative input terminal φ of the first NAM circuit (3), and a predetermined reference pulse pr is supplied to the other input terminal φ.
Supply to 2. As shown in the second diagram, this reference pulse pr has the same positive/negative directionality as the above-mentioned difference signal (2) in terms of its output timing, that is, the pulse period T is one pixel output period t of the above-mentioned image pickup signal V in. Similarly, the pulse width n is equal to 1/2 pulse period, and the amplitude A is greater than or equal to the recent potential vr at least in the positive and negative directions. Therefore, the output terminal φ3 of the first NAM circuit (3)
Output signal output from■.

As shown in FIG. 2E, the signal component of the portion of the difference signal ■ on which the reset noise (indicated by O1×, △ in the figure) is superimposed is the positive pulse waveform of the reference pulse pr. The signal waveform is replaced by .

Here, the circuit configuration shown in FIG. 3 can be used as the first NAM circuit (3). That is, when the potential of the differential signal ① input to the negative input terminal φ1 is higher than the potential of the reference pulse pr input to the other input terminal φ2, the negative NPN transistor Q,
acts as a so-called emitter follower, and the other NPN transistor Q2 is turned off, so that the potential (differential signal V,) input from the output terminal φ to the base of one NPN transistor Q appears as is. Next, when the potential of the differential signal ■ becomes lower than the potential of the reference pulse pr, one NPN) transistor Q is turned off, and the other NPN) transistor Q2 acts as an emitter follower, so the other NPN) The potential input to the base of transistor Qt (reference pulse p
r) appears as is at the output terminal φ3. in this way,
In the first ONAM circuit (3), a high level signal component of the difference signal ■ and the reference pr is selected and outputted from the output terminal φ3 as an output signal ■□.

Of this output signal (1), for example, after cutting off the reference pulse waveform, it may be passed through a low-pass filter to obtain a baseband signal free of reset noise.

However, in this example, the output signal ■□ from the first NAM circuit (3) is directly supplied to the negative input terminal φ4 of the second NAM circuit (5), and the output signal 2
The above output signal ■8 supplied to the delay line (4) of
is phase adjusted by the second delay line (4) (1 of 1 pixel output period t in the imaging signal V in of FIG. 2A)
The delayed output signal VHd, shown in FIG. And this second NAM circuit (5)
Of the above output signal ■9 and delayed output signal ■□,
A low-level signal component is selected, and an output signal (2) in which the reset pulse component Sr and the imaging signal component S are adjacent to each other is obtained from the output terminal φ6, as shown in FIG. 2C.

Here, the circuit configuration shown in FIG. 4 can be used as the second NAM circuit (5). That is, when the potential of the output signal 8 input to the negative input terminal φ is lower than the potential of the delayed output signal VHt1 input to the other input terminal φ, one PNP) transistor Q3 acts as an emitter follower, and the other PNP) transistor Q4 is turned off, so that the potential input to the base of one PNP) transistor Q3 from the output terminal φ is
The output signal VH) appears as is. Next, the output signal v
When the potential of H becomes higher than the delayed output signal V144, one PNP transistor Q is turned off, and the other PNP transistor Q4 acts as an emitter follower, so that the base of the other PNP transistor Q4 is The potential input to the output terminal φ6 (delayed output signal ■□) appears as is at the output terminal φ6.

In this manner, in the second NAM circuit (5), the low level signal component is selected from the output signal vH and the delayed output signal V□, and is outputted as the output signal V from the output terminal φ.

Then, by supplying this output signal ■ to the low-pass filter (6), the output terminal φ is output. ut to Figure 2 1]
Baseband signal without reset noise shown in ■. ut
get.

As described above, according to this example, since switching operations such as zumbling are not performed, the input image pickup signal V
Even if the bandwidth of in is broadened due to the increase in the number of pixels of the CCD image sensor, it is possible to easily and reliably remove correlated noise (reset noise, etc.) from the image signal Vin, and also to remove the correlation noise. There is also little aliasing of high-frequency noise, and a sufficient noise suppression effect can be obtained.

In particular, the output signal 8 obtained from the first NAM circuit (3) is directly transmitted to the second NAM circuit via the second delay line (4).
Since the output signal (■) in which the reset pulse component Sr and the imaging signal component S are adjacent to each other is obtained from the output terminal φ6 by supplying it to the ONAM circuit (5), the imaging signal V due to the removal of reset noise is In loss can be almost eliminated, and highly accurate signal processing can be performed in the subsequent signal processing system.

〔Effect of the invention〕

According to the image signal noise suppression circuit according to the present invention, it is possible to easily and reliably remove noise from the image signal, which has become broadband due to the increase in the number of pixels in CCD type image sensors, etc. In the signal processing system, it becomes possible to perform highly accurate signal processing.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a noise suppression circuit for an imaging signal according to this embodiment, and FIG. 2 is a waveform diagram showing its signal processing.
3 is a circuit diagram showing an example of the first NAM circuit according to the present embodiment, FIG. 4 is a circuit diagram showing an example of the second NAM circuit according to the present embodiment, and FIG. 5 is a circuit diagram showing an example of the second NAM circuit according to the present embodiment. Fig. 6 is a waveform diagram showing its signal processing, and Fig. 7 is a block diagram showing its signal processing.
The figure is a block diagram showing another conventional example (delay difference method).
The figure is a waveform diagram showing the signal processing. (A) is a noise suppression circuit, (1) is a first delay line, (2) is a delay difference circuit, (3) is a first NAM circuit,
(4) is the second delay line, (5) is the second ONAM
The circuit (6) is a low-pass filter.

Claims (1)

[Claims] 1. A delay difference circuit that takes a difference between an input imaging signal and a delayed imaging signal obtained by delaying the input imaging signal by a delay line, and a difference signal from the delay difference circuit is input separately. An imaging signal noise suppression circuit comprising a mixing circuit that outputs a high-level signal component of a predetermined reference pulse. 2. A delay difference circuit that takes a difference between an input imaging signal and a delayed imaging signal obtained by delaying the input imaging signal by a first delay line, and a predetermined difference signal that is input separately from the difference signal from the delay difference circuit. a first mixing circuit that outputs a high-level signal component among the reference pulses; and a delayed output obtained by delaying the output signal from the first mixing circuit and the output signal by a second delay line. A noise suppression circuit for an image pickup signal, comprising a second mixing circuit that outputs a low-level signal component of the signal.