JP2884191B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device using a current-output amplifying solid-state imaging device as a pixel.

[0002]

2. Description of the Related Art In recent years, the development of an amplification type imaging device as a new solid-state imaging device replacing the MOS type and the CCD type has been activated. The amplification type imaging device includes a charge modulation device (CMD) of a type in which the photoelectrically converted charge is extracted as a current output amplified by an internal amplification device.
Which is abbreviated as), and has been introduced in the 1989 National Convention of the Institute of Television Engineers of Japan 2-11.

Next, a configuration example of a solid-state imaging device using such a CMD as a pixel will be described with reference to FIG. CMD1-11, 1-12,... 1-mn constituting each light receiving pixel, and CMD1-1.n + 1, 1-1.n + 2,. + i are arranged in a matrix, and each drain has a power supply V _DD (> 0)
Is applied. The gate terminals of the CMD groups in each row arranged in the horizontal direction are connected to the row lines 2-1, 2-2,... 2-m, and the source terminals of the CMD groups in each column arranged in the vertical direction are Connect to column lines 3-1, 3-2,... 3-n, 3-n + 1,. The column lines 3-1, 3-2, ... 3-n, 3-n + 1, ... 3-n + i are column selection transistors 4-1, 4-2, ... 4, respectively. -n, 4-n + 1, ... 4-n + i
, And anti-selection transistors 5-1, 5-2, ... 5-n, 5-n + 1,
.. Are commonly connected to a video line 6 and a line 7 grounded to GND via 5-n + i. The video line 6 is connected to a current-voltage conversion type preamplifier 8 whose input is virtually grounded, and an output terminal 9 of the preamplifier 8 reads a video signal of negative polarity in a time series.

[0004] In the solid-state image pickup device thus configured, the signal of each pixel is supplied to the vertical scanning circuit 10 and the horizontal scanning circuit 11.
Are scanned and output. That is, the vertical scanning circuit 10
, Each row line is sequentially selected at one horizontal period interval. The horizontal scanning circuit 11 scans during a period in which one row is selected, and each column line is sequentially connected to the video line 6 via a column selection transistor, so that the output voltage of each selected pixel becomes a current. _-Appears at the output terminal 9 as the voltage output _VOUT via the voltage conversion type preamplifier 8.

[0005] An output waveform appearing at the output terminal 9 is shown in FIG. As shown in this figure, in the 1H period, there are a video output period T ₁ , a light-shielded output period T _2, and a non-signal period T ₃ ,
Video output period T ₁ is receiving pixel 1-11, 1-12, ... in 1-mn period signal is output, the light blocking output period T ₂ pixels that are shielded 1-1 · n + 1, · ··· 1-1 · n + i,... 1-m · n + 1,... 1-m · n + i. Also, in the no-signal period T _3, which pixels may not been selected, the signal current is not output, and has a GND level. In normal imaging operation, the light shielding output period T _2, and the no-signal period T ₃ is operating is performed such that the blanking period (HBLK).

[0006]

By the way, the C of the above-mentioned structure is used.
When imaging a dark subject in the MD solid-state imaging device, the following problem occurs. That is, in the case of imaging a dark subject, since the signal current output is small, the feedback resistance R of the current-voltage conversion type preamplifier 8 must be increased in order to increase the gain. However, as shown in FIG. 12, even if the feedback resistor R is increased to some extent, if the offset current between the GND level and the OB level is larger than the signal current, the signal component is sufficiently amplified due to the limitation of the dynamic range of the preamplifier. Previously, the offset current saturates the preamplifier range. For this reason, after the current-voltage conversion by the preamplifier, the voltage must be further amplified by performing OB clamping or the like, but such a configuration is disadvantageous in terms of S / N.

[0007] In the case of a current output type CMD solid-state imaging device, it is possible to relatively easily obtain an added output of a plurality of pixels. For this reason, a configuration is conceivable in which an addition output is generated only when the subject is dark and the video signal level is low.In this case, when a large number of pixel outputs are simply added, the preamplifier is turned off by the dark offset current component of each pixel. The range is saturated. For this reason, in order to obtain an effective added output, there is a problem that the offset current must be removed by some method.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem in a conventional solid-state imaging device using an amplifying type solid-state imaging device of a current output type as a pixel. An object of the present invention is to provide a solid-state imaging device in which the dynamic range of a conversion-type preamplifier can be used effectively.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a solid-state imaging device using, as a pixel, an amplifying solid-state imaging device for extracting a photoelectrically converted charge as a current output amplified by an internal amplification device. In the imaging apparatus, an imaging pixel and a light-shielded pixel arranged in the horizontal scanning direction, circuit means for sequentially reading the imaging pixel, and light shielding on the same horizontal scanning line during a period for sequentially reading the imaging pixel in the horizontal scanning direction. Circuit means for simultaneously reading the output of the pixel, and a current source for drawing the same current as the light-shielded pixel output current,
The current output terminal of the current source is connected to the readout output terminal of the imaging pixel.

With this configuration, the dark offset current component is removed from the output current of each imaging pixel, and only the signal current component is extracted. The current component is amplified by the current-voltage conversion amplifier. Therefore, when the signal current output is small in imaging a dark subject or the like, even if the gain of the amplifier is increased, the range of the amplifier is not saturated by the offset current at dark, and the dynamic range of the amplifier can be used effectively. .

[0011]

Next, an embodiment will be described. FIG. 1 is a circuit configuration diagram showing a basic embodiment of a solid-state imaging device according to the present invention. The same or equivalent members as those of the conventional solid-state imaging device shown in FIG. I have. In this embodiment, the present invention is applied to a line sensor constituted by pixels of only one row, and among n + 1 pixels 1-1,... 1-n + 1,
The pixels 1-1,..., 1-n are normal imaging pixels that generate an output according to the amount of incident light, and the pixels 1-n + 1 are light-shielded pixels. The sources of the imaging pixels are selection switches 4-1,..., 4-n for selecting connection to the video line 6 and anti-selection switches 5-1,..., Connected to the line 7 grounded to GND. 5-n, and the selection switches 4-1,.
Are sequentially driven, thereby sequentially selecting the imaging pixels 1-1,... 1-n, and the current output of each imaging pixel appears on the video line 6.

On the other hand, the selection switch 4-n + 1 connected to the source of the light-shielded pixel 1-n + 1 is connected to the dark output signal line 16, and the dark output signal line 16 outputs an output corresponding to the reference signal current. It is connected to a current source 19 that generates a current. The current source 19 generates a current I _O equal to the current value I _ref of the dark output signal line 16 to the current source output line 17 (as described later, the output of the current source output line 17 The current _IO may be m times the current value _Iref of the dark output signal line 16).
The current source output line 17 is connected to the video line 6, the signal line 18 beyond the connection point is connected to the virtually grounded current-voltage conversion preamplifier 8, and the voltage output V from the output terminal 9.
_OUT is generated.

FIG. 2 shows selection pulses φ ₁ ,.
· · Phi _n and the light shielding pixel timing of the selection pulse phi _D, and video line 6, the current source output line 17, the output current I of the signal line 18
_sig , _{IO, and Isig- IO} . Selection pulse φ ₁ , ...
In φ _n , a pulse is sequentially transmitted, and an output of a pixel corresponding to the pulse appears in an output current _Isig of the video line 6. The light-shielded pixel selection pulse φ _D is the selection pulse φ ₁
There time to become "H" selection pulse phi _n from becomes "H", "H" is in the state, the period, the dark output signal line 16 the output of light-shielded pixel 1-n + 1 A current I _ref appears,
A similar output current I is applied to the current source output line 17 via the current source 19.
_O occurs. Then, a difference output current I _sig −I _O between the output current I _sig of the video line 6 and the output current I _O of the current source output line 17 is generated in the signal line 18. This difference output current is obtained by subtracting the offset current from the (offset current + signal current) output from each imaging pixel, and the voltage output appearing through the current-voltage conversion preamplifier 8 is based on the signal GND. The waveform has an inverted voltage. In this method, since the GND is at the black level, if the video signal is small, the gain can be increased and the amplitude can be increased, and the dynamic range of the current-voltage conversion preamplifier can be used effectively.

Next, FIG. 3 shows a circuit configuration of a second embodiment of the present invention. This embodiment is a specific embodiment in which the present invention is applied to an area sensor, and includes an arrangement of pixels, a vertical scanning circuit,
The connection configuration of the column selection transistor and the anti-selection transistor is the same as that of the conventional CMD solid-state imaging device shown in FIG. 10, and corresponding members are denoted by the same reference numerals. In the present invention, the selection transistor of any one of the light-shielded pixel columns, in this embodiment, the selection transistor
The output terminal of 4-n + i is connected to a dark output signal line 16, and a current value of the dark output signal line 16 is supplied to a current source output line 17 via a current source 19 having the current value I _ref as a reference value. The same current I as I _ref
O is configured to flow. The current source output line 17 is connected to the video line 6, and the signal line
Reference numeral 18 is connected to the input terminal of the current-voltage conversion preamplifier 8 having a virtual ground, and a voltage output appears at the output terminal 9 via the preamplifier 8. The other light-shielded pixel columns are configured such that the anti-selection transistors 5-n + 1,..., 5-n + i-1 are always in the ON state, and the current output is discharged to GND. I have. In this embodiment, the rightmost pixel column is selected as the reference light-shielded pixel column connected to the dark output signal line 16, but any of the light-shielded pixel columns can be selected as the reference light-shielded pixel column. Although it is possible, it is desirable to select a pixel row in which characteristics are less likely to vary due to layout or process factors.

Next, the operation of the solid-state imaging device thus configured will be described. FIG. 4 shows the timing of the selection pulses φ ₁ ,... Φn _{+ 1} of the horizontal scanning circuit 11 and the selection pulse φ _D of the light-shielded pixel row, the video line 6, the current source output line 17, and the signal line 18.
The output currents I _sig , I _O, I _sig −I _O , and the output voltage V _OUT of the output terminal 9 are shown. As can be seen from Figure 4, selection pulses phi ₁ of the fall of the selection pulse phi _n from the rise (φ _{n + 1} rise) time to, dark output current I from the output current I _sig of CMD pixels for each imaging _ref
Since (= I _O ) is subtracted, the output voltage V _{OUT at the} output terminal 9 has an offset removed from the output voltage shown in FIG. Therefore, even when a dark subject is imaged and the video signal component is small, the gain can be increased by increasing the feedback resistance R of the preamplifier 8 and a large signal voltage can be obtained in the first stage.

Next, the dark output current I _ref from the light-shielded pixel
Current source that draws the same current I _O with reference to
The nineteenth configuration will be described. FIGS. 5 and 6 are diagrams showing circuit configuration examples to which a current mirror circuit is applied as an example. In FIG. 5, MOS transistors M ₁ and M _{2 form} a current mirror circuit, and generate a current I _O equal to the reference current I _ref if the transistor size of the MOS transistors M ₁ and M ₂ is the same. MOS transistor M ₃ and the resistor R ₁ is the potential V ₁ of the drain of the MOS transistor M ₂ (the gate of the MOS transistor M _1, M ₂₎ is connected to the GND level. FIG. 6 shows MOS transistors M ₁ , M ₂ , M ₄ , and M ₅ as 2
This is a configuration example using a current mirror circuit configured by stacking. The MOS transistors M ₃ and M ₆ have the potential V ₁ of the drain (gate of the MOS transistors M ₁ and M ₂ ) of the MOS transistor M ₂ , as in the configuration example shown in FIG.
Is provided to set the GND level. By using the current mirror circuit in this manner, a reference current source for removing an offset current can be simply configured.

The embodiment shown in FIG. 3 is configured to correspond to the case where pixel outputs are read out one pixel at a time. However, in the case of simultaneous reading of multiple pixels of two or more pixels, the dark offset current for reference is also used. By adding the same number of output currents of light-shielded pixels as the number of readout pixels, an offset current component can be removed from the mixed output current of the imaging pixels. Also, when the number of readout pixels is changed according to the brightness of the subject, the offset current can be removed by controlling to read out the corresponding number of light-shielded pixels.

FIG. 7 shows a circuit configuration of a third embodiment having such a function. In the embodiment shown in FIG. 3, the light-shielded pixel output is read out from a fixed column. In this embodiment, the decoder 12 turns on and off the column selection transistor of the light-shielded pixel. The decoder 12 is controlled by an external control unit 20. Also control unit
20 is configured to control the number of pixels read out by the horizontal scanning circuit 11 by also controlling the external clock driver 21.

In the solid-state imaging device configured as described above, the number of light-shielded pixels corresponding to the number of pixels read out by the horizontal scanning circuit 11 is selected by the decoder 12, whereby
Offset current components for an arbitrary number of readout pixels can be removed. Thus, a bright object is read out with a single pixel, while a dark object is read out with a plurality of pixels.
Even if the number of readout pixels is controlled, the dynamic range of the current-voltage conversion preamplifier can be effectively used.

In each of the embodiments described above, the number of readout imaging pixels and the number of light-shielded output pixels are made to coincide with each other. Of these, in particular, the imaging pixels are read out one by one. However, there is a problem that an error easily occurs between the black level of the readout pixel and the output level of the light-shielded pixel due to the influence of variations in the process or layout. In order to reduce the influence of such variation, it is more effective to take out the average value of the outputs of several rows of light-shielded pixels.

FIG. 8 shows a circuit configuration of a fourth embodiment having such a function. In this embodiment, the outputs of the light-shielded pixel columns in the second embodiment shown in FIG. 3 are added by i columns, and the light-shielded pixel selection transistors 4-n + 1,.
Through the -n + i, the added dark output currents _{Iref of} the light-shielded pixel columns n + 1 to n + i flow through the dark output signal line 16. To determine the average value of this addition the dark output current I _ref is provided between the current source output current I _O and the addition the dark output current I _ref, it may be established following equation. I _O = I _ref × 1 / i As a circuit configuration of the current source 19 that satisfies such a relationship, the MOS transistor M in the current source shown in FIG.
The aspect ratio W / L of the gates of ₁ and M ₂ may be set as follows. W / L of M ₁ : W / L of M ₂ = 1: i In the fourth embodiment configured as described above, the average output of the light-shielded pixel column can be used as the dark output level. Influence is reduced.

Next, an embodiment in the case where the number of simultaneously read pixels is larger than the number of light-shielded pixel columns will be described. In some special applications of the area sensor, the addition output of all the pixels in one row may be required. In this case, it is very inefficient to lay out the light-shielded pixels on the same number of chips as the imaging pixels. In such a case, in the embodiment shown in FIG.
The ratio between the current source output current I _O and the dark output current I _ref may be set to 1 or more, and the value of the current source output current I _O may be equivalently set to be equal to the offset current value of the number of readout pixels. For example, when n = 256 and i = 16, and all the pixels for imaging in one row are read out simultaneously, that is, when 256 pixels are read out at the same time, the circuit configuration of the reference current source 19 may be set as follows. _{I O = 256/16 × I} ref = 16 × I ref circuit such a current source, W / L of the MOS transistor M ₁ of the W / L of the MOS transistor M ₂ in the current source with the configuration shown in FIG. 5 Can be realized by setting the following ratio. M ₁ of W / L: M ₂ of W / L = 16: 1 Thus, by varying the current ratio of the reference current I _ref and the current source output current I _O of the current source 19, any number of read pixels The offset current can be removed.

FIG. 9 shows a circuit configuration for arbitrarily changing the current ratio between the reference current _Iref of the current source 19 and the output current _IO by external control. This circuit configuration is a kind of current draw type D / A converter. MOS transistors M ₁ and ~M ₇ size the same, MOS transistor M ₈ ~M ₁₄ is configured to have a ratio as follows. W / L of M _8: the _{M 9 W / L: ····:} M 14 of W / L = 1/4: 1/4: 1/2: 1: 2: 4: 1 and each resistor R ₁ the ratio of to R ₉ are set as follows. R ₁ : R ₂ : R ₃ : R ₄ : R ₅ : R ₆ : R ₇ : R ₈ : R
₉ = 2: 2: 2: 2: 1: 1/2: 2: 1: 1 If the ratio of each MOS transistor and each resistor is set as described above, the current flowing through the MOS transistors M _{1 to} M ₆ Is 1/4: 1/4: 1/2: 1: 2: 4
Becomes As Here, the reference current I _ref, if an electric current flows in the light-shielded pixels of four columns, each current value flowing through the MOS transistor M ₁ ~M ₆ whereas the offset current when dark, 1: 1:
2: 4: 8: 16. Current component flowing through the MOS transistor M ₁ is always made to appear in the current source output current I _O, and the current flowing through the MOS transistor M ₂ ~M _6, the switch S by an external control unit 23
W ₁₁ , SW ₂₁ , SW ₃₁ , SW ₄₁ , SW ₅₁ are turned on respectively
SW ₁₀ , SW ₂₀ , SW ₃₀ , SW ₄₀ , and SW ₅₀ are turned off.
The current source output current I _O appears when F is applied. The SW _11, SW _21, a · · · SW ₅₁ OF
If F, it does not appear in the output current _IO . Therefore, the ON / OFF control of these switches makes it possible to control and supply a current of 1 to 32 times the dark offset current as the current source output current _IO .

Therefore, by using the current source having the above configuration, even if the number of readout pixels changes between 1 and 32, the output signal current including the dark offset current is controlled by the external control unit 23. , It is possible to remove the dark offset current. Although the current source shown in FIG. 9 is constituted by a 5-bit D / A converter, it is needless to say that by increasing the number of bits of the D / A converter, a wider range of pixels can be simultaneously read. Can respond.

Although the current source in each of the above embodiments is configured using a MOS transistor, there is no problem if it is configured using another device such as a bipolar transistor.

In each of the above embodiments, the CMD is used as an amplifying solid-state image sensor constituting a pixel. Also, when the readout method of each image sensor is a current output type, the present invention can be applied, and the same operation and effect that the dynamic range of the current-voltage conversion type preamplifier can be effectively used can be obtained. .

[0027]

As described above with reference to the embodiments,
According to the present invention, before performing the current-voltage conversion process on the output current of the imaging pixel with the current-voltage conversion amplifier, unnecessary dark offset current is removed as an output from the output current. When the signal current output is small in imaging a dark subject or the like, even if the gain of the amplifier is increased, the offset current does not saturate the range of the amplifier, so that the dynamic range of the amplifier can be used effectively.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation of the first embodiment.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a signal waveform diagram for explaining the operation of the second embodiment.

FIG. 5 is a circuit diagram showing a configuration example of a current source.

FIG. 6 is a circuit diagram showing another configuration example of the current source.

FIG. 7 is a circuit diagram showing a third embodiment of the present invention.

FIG. 8 is a circuit configuration diagram showing a fourth embodiment of the present invention.

FIG. 9 is a circuit diagram showing a configuration example of a current source according to a fifth embodiment of the present invention.

FIG. 10 is a circuit configuration diagram illustrating a configuration example of a conventional solid-state imaging device.

FIG. 11 is a diagram illustrating a signal waveform during normal operation in a conventional solid-state imaging device.

FIG. 12 is a diagram illustrating a signal waveform at the time of imaging a dark subject in a conventional solid-state imaging device.

[Explanation of symbols]

 1-1, ... 1-n Imaging pixel 1-n + 1 Shading pixel 4-1, ... 4-n + 1 Select switch 5-1, ... 5-n + 1 Non-select switch 6 Video line 7 Ground line 8 Current-voltage conversion amplifier 11 Horizontal scanning circuit 16 Dark output signal line 17 Current source output line 18 Signal line 19 Current source

Claims (5)

(57) [Claims] 1. A solid-state imaging device using, as a pixel, an amplifying solid-state imaging device that takes out a photoelectrically converted charge as a current output amplified by an internal amplification device. Circuit means for sequentially reading out pixels and imaging pixels, circuit means for simultaneously reading out the outputs of light-shielded pixels on the same horizontal scanning line during a period in which image-taking pixels in the horizontal scanning direction are sequentially read out, A current source that draws in the current, a current output terminal of the current source is connected to a readout output terminal of the imaging pixel, a dark offset current component of each imaging pixel is removed, and only a signal current component is extracted. A solid-state imaging device characterized by being configured to amplify with a voltage conversion amplifier. 2. The solid-state imaging device according to claim 1, wherein said current source is constituted by a current mirror circuit. 3. A solid-state imaging device using pixels as amplification type solid-state imaging elements that take out photoelectrically converted charges as current output amplified by an internal amplification element. Circuit means for sequentially reading out the mixed output of the plurality of pixels for imaging,
Circuit means for simultaneously reading the mixed output of the same number of light-shielded pixels on the same horizontal scanning line during the period of sequentially reading the mixed output of a plurality of imaging pixels in the horizontal scanning direction, and a current source for drawing the same current as the mixed output current of the light-shielded pixels And a configuration in which the current output terminal of the current source is connected to the readout output terminal of the imaging pixel, the offset current at dark is removed from the mixed output current of the imaging pixel, and the current is amplified by the current-voltage conversion amplifier. A solid-state imaging device characterized by the following. 4. A solid-state imaging device using, as a pixel, an amplifying type solid-state imaging device that takes out a photoelectrically converted charge as a current output amplified by an internal amplification device, and a pixel for imaging arranged in a horizontal scanning direction and light-shielded light. Circuit means for sequentially reading a mixed output of any number of imaging pixels, and a plurality or a single light-shielded pixel on the same horizontal scanning line during a period of sequentially reading a mixed output of any number of imaging pixels in the horizontal scanning direction And a current source for drawing a current of an integral multiple or a fraction of the output current of the light-shielded pixel. The current output terminal of the current source is connected to the read output terminal of the imaging pixel. The dark-time offset current is removed from the mixed output current of an arbitrary number of imaging pixels to obtain a current −
A solid-state imaging device characterized by being configured to amplify with a voltage conversion amplifier. 5. The method according to claim 1, wherein the current source is a current draw type D / A.
The solid-state imaging device according to claim 4, wherein the solid-state imaging device is configured by a converter.