JPS6019369A - Image sensor - Google Patents

Abstract

PURPOSE:To make an output signal level constant by controlling a gate part with an output of a count circuit generating one pulse respectively at every prescribed number of clock pulses, transferring in parallel an electric charge generated in a photodetecting section to a charge transfer part and outputting it from an output terminal as a serial light signal. CONSTITUTION:An internal clock generating circuit 7 generates a clock pulse train and just after a scanning signal is inputted to a count circuit 8 and further n-set of pulses are counted, one pulse is generated and outputted. An output of the count circuit 8 is fed to a terminal 4 of the gate part 2 and the electric charge stored in each photodiode of the photodetecting section 1 is transferred to each CCD of a charge transfer section 3. The electrc charge stored in a CCD array of the charge transfer section 3 is transferred to the right by the clock pulse train inputted from the terminal 5, outputted from a terminal 6 as a signal output, an analog switch 10 is closed only for one section of exposure sections S1- S4 and the signal is outputted from an output terminal 12.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a driving method for an image sensor, particularly a line sensor.

In a one-dimensional image sensor, signals photoelectrically converted by photodiodes arranged in a row are accumulated in parallel in a charge-coupled device (hereinafter referred to as CCI) or a field-effect device, and these accumulated charges are transferred in series. Outputs the button as an optical signal output. A conventional method for a CCD type image sensor will be explained below. Figure 1 shows C(j)
FIG. 2 is a diagram showing the configuration of a shaped image sensor. The light receiving section 1 is a photodiode array, and the gate section 2 is a transfer gate array.

The charge transfer section 3 is composed of a CCL play, and is driven as follows. First, a scanning signal pulse is applied to the terminal 4 of the gate section 2 to put all transfer gate arrays into the transfer state, and the charges accumulated in the photodiode array of the light receiving section 1 are transferred in parallel to the CCD array of the charge transfer section 3. ,
The charges accumulated in each CCD are sequentially transferred to the right by a four-pulse train from terminal 5, and are output from terminal 6 as a serial signal output. Therefore, the light intensity in one-dimensional space received by the photodiode array can be temporally corrected and obtained from the terminal 6 as a fin electric signal. As shown in FIG. 2, the relationship between the fogging time and the output signal level in the photodiode initially increases in proportion to the exposure time, but then saturates. In the above driving method, the period of the scanning signal pulse applied to the gate section 2 becomes the exposure time, so the scanning period must be kept constant so that the exposure is performed in the linear region shown in FIG. However, when using an image sensor, there are cases where it is desired to make the scanning period variable, and in such cases, a simple scanning method has the disadvantage that the output signal level (sensitivity) is not constant or is saturated.

An object of the present invention is to eliminate the above-mentioned drawbacks and to provide an image sensor having a driving method in which the sensitivity remains unchanged even when the scanning period is made variable. It does not directly use a scanning signal, but has two terminals for inputting a scanning signal and a clock pulse, and generates one pulse each when a scanning signal is input and for each fixed number of clock pulses input thereafter. The gate section is controlled by the output of the counting circuit, and the charges generated in the light receiving section are transferred in parallel to the charge transfer section, and the charges are sequentially transferred by the clock pulse and output as a serial optical signal from the output terminal. .

The present invention will be described in detail below with reference to the drawings.

FIG. 3 shows an embodiment of the present invention, in which the present invention is applied to a CCD type image sensor. FIG. 4 is a diagram showing signal waveforms for each part of FIG. 3. 7 is an internal clock generation circuit, 8 is a count circuit, 9 is a section selection circuit, and IO is an analog switch. The internal clock generating circuit 7 generates a clock pulse train, and the counting circuit 8 generates a clock pulse train immediately after the scanning signal is input and every time it counts n pulses.
Each generates and outputs one pulse. scanning signal.

The clock pulse and the output waveforms of the count circuit 8 are shown in FIGS. 4(a), 4(b), and 4(c), respectively.

The output of the count circuit 8 is applied to the terminal 4 of the gate section 2.

Charges stored in each photodiode of the light receiving section 1 are transferred to each CCD of the charge transfer section 3. After that, the photodiode starts accumulating optical signal charges again, so the output pulse interval T(1+-1,, 1t-11) of the count circuit 8 in FIG. 4(C)
, 1, -1,) becomes the regular fog light time.

T becomes nTo (T is the clock pulse period), and the internal clock generation circuit 7. The count circuit 8VC is determined by the scanning signal pulse and is not synchronized with the scanning signal pulse. Therefore, as shown in FIG.
)oSt(, t+-) + Ss (tt~ts)
The interval is the same time T, but the last 84 (t3~to
) section becomes T', which is an odd time shorter than T.0 The charges accumulated in the CCD array of the charge transfer section 3 are input from the terminal 5 and transferred to the right side by the clock pulse train (Fig. 4 (b)). The signal is output from the terminal 6 as a signal output (@4 (d)). The signal from terminal 6 is the exposure period S, S
The analog switch 10 is closed for only one section of 4, and the output is output from the output terminal 12. This section selection is performed by the section selection circuit 9 receiving the scanning signal pulse and the output pulse of the counting circuit 8 and outputting a switch control signal. Next, section selection will be explained. The waveforms of each section in FIG. 4(d) are all obtained by combining the waveforms of the optical signals exposed in the previous section. Section S! is exposed in section S4 of the previous frame, and section S4 is excluded because the grouping time is T'(<T). The signal in section S4 is
Although the exposure itself was carried out in the period S3 of the regular time T, a complete signal output was not achieved because the charge transfer was not complete. In addition, the remaining charges also affect the output of the next frame section SI. Therefore, the interval S 1 ,
The normal output will be sent only to S3. Among them, the signal for section 8 is passed through the section selection circuit 9 by turning on the analog switch 10. The scanning signal of the image sensor of the present invention and the signal waveform of the output terminal 12 are shown in FIGS. 5(a) and 5(b), respectively. Here, approximately T means T-T+T because the scanning signal pulse and clock pulse are not synchronized as shown in FIGS. 4(a) and 4(b).

This is because it takes a value between. Note that the waveform in (C) is a waveform from which noise has been removed. This is the same as the sections S, , S3. This is because if the section length is made too large, the output signal level of the photodiode will enter the saturation region, which will also cause not all charges to be transferred, making it impossible to obtain a stable output signal level.

As explained above, the image sensor according to the present invention can maintain constant sensitivity even if the scanning period changes.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a part of a CCD type image sensor, FIG. 2 is a diagram showing the sensitivity characteristics of a photodiode, FIG. 3 is a diagram showing an embodiment of the present invention, and FIG. FIG. 5 is a diagram showing waveforms of various parts of the circuit, and FIG. 5 is a diagram showing a scanning signal and an output signal in an embodiment of the present invention. 1... Light receiving part, 2... Gate part, 3...
... Charge transfer section, 4 ... Control signal input terminal, 5 ... Clock pulse input terminal, 6 ...
... Charge transfer unit output terminal, 7 ... Clock pulse generation circuit, 8 ... Count circuit, 9 ...
...Section selection circuit, 1o...Analog switch% 11...Scanning signal input terminal, 12...
...Image sensor output terminal. Agent Patent Attorney Uchihara 8 days

Claims (2)

[Claims] (1) A one-dimensional image sensor consisting of a light receiving section, a gate section, and a charge transfer section, which has two terminals for inputting scanning signals and clock pulses, and has a fixed number of terminals that are input when and after the scanning signal is input. The gate section is controlled by the output of a counting circuit that generates one pulse for each clock pulse, and the charges generated in the light receiving section are transferred in parallel to the charge transfer section, and the charges are sequentially transferred and output according to the clock pulse. An image sensor that outputs serial optical signals from one end. (2) From the serial optical signal from the output terminal of the charge transfer section, only one section that is not adjacent to the scanning signal is passed among the sections partitioned by the gate section control pulse within the scanning signal period. The image sensor according to claim 1, wherein the image sensor outputs the output of the image sensor.