JPH0122793B2 - - Google Patents

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 a row of photodiodes are stored in parallel in a charge-coupled device (hereinafter referred to as CCD) or a field-effect device, and these accumulated charges are transferred in series. It is extracted and output as an optical signal output. The conventional method for CCD type image sensors will be explained below. FIG. 1 is a diagram showing the configuration of a CCD type image sensor. The light receiving section 1 consists of a photodiode array, the gate section 2 consists of a transfer gate array, and the charge transfer section 3 consists of a CCD array.
The driving is performed as follows. First, a scanning signal pulse is applied to the terminal 4 of the gate section 2 to put all the transfer gate arrays into a transfer state, and the charges accumulated in the photodiode array of the light receiving section 1 are transferred to the charge transfer section 3.
After being transferred in parallel to the CCD array, the charges accumulated in each CCD are sequentially transferred to the right by a clock pulse train from terminal 5, and are outputted from terminal 6 as a serial signal output. Therefore, the light intensity in one-dimensional space received by the photodiode array can be obtained from the terminal 6 as a temporally serial electric signal. As shown in FIG. 2, the relationship between the exposure time and the output signal level in the photodiode array 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.

SUMMARY OF THE INVENTION 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.

The image sensor according to the present invention does not directly use a scanning signal as a gate control signal, but has two terminals for inputting a scanning signal and a clock pulse, and a fixed number of clock pulses are input when the scanning signal is input and after that. The gate section is controlled by the output of a counting circuit that generates one pulse for each predetermined section within the scanning signal period when counting the number of pulses, and the charges generated in the light receiving section are transferred in parallel to the charge transfer section. A charge transfer section that sequentially transfers charges using clock pulses and outputs them in series from the output end, for one section that is not adjacent to the scanning signal among the sections divided by the output pulses of the counter within the scanning signal period. Only the output of is passed through and is used as the output signal.

The present invention will be described in detail below with reference to the drawings. FIG. 3 shows an embodiment of the present invention, which is applied to a CCD type image sensor. Figure 4 is the third
FIG. 3 is a diagram showing signal waveforms at various parts in the figure. 7 is an internal clock generation circuit, 8 is a count circuit, 9 is a section selection circuit, and 10 is an analog switch. The internal clock generating circuit 7 generates a clock pulse train, and the counting circuit 8 generates and outputs one pulse immediately after the scanning signal is input and every time it counts n pulses.
The scanning signal, clock pulse, and output waveforms of the counting circuit 8 are shown in FIGS. 4a, b, and c, respectively. The output of the count circuit 8 is connected to the terminal 4 of the gate section 2.
The charges added to the photodiodes of the light receiving section 1 are transferred to the CCDs of the charge transfer section 3. After that, the photodiode starts accumulating optical signal charges again, so the output pulse interval T (t ₁ - t ₀ , t ₂ - t ₁ , t ₃ - t ₂ ) of the count circuit 8 in FIG. 4c is the regular exposure time. become. T is nT ₀ (T ₀ is the clock pulse period)
This is determined by the internal clock generating circuit 7 and the counting circuit 8, and is not synchronized with the scanning signal pulse. Therefore, as shown in FIG. 4, the exposure time is the same time T in the sections S ₁ (t ₀ - t ₁ ), S ₂ (t ₁ - _{t 2} ), and S ₃ (t ₂ - _{t 3} ), but The final S ₄ (t ₃ -t ₄ ) interval is T', which is an odd time shorter than T. The charges accumulated in the CCD array of the charge transfer section 3 are transferred to the clock pulse train input from the terminal 5 (Fig. 4b).
is transferred to the right side and the signal is output from terminal 6 (4th
Figure d) is output. The signal from terminal 6 is
Analog switch 1 only for one exposure period _S1 to _S4
0 is closed 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 in each section of FIG. 4d are all the waveforms of the optical signals exposed in the previous section. The section S ₁ is exposed in the section S ₄ of the previous frame, and the section S ₄ is excluded because the exposure time is T'(<T). Although the exposure itself was performed in the interval _S3 of the regular time T, the signal in the interval _S4 is not a complete signal output because the charge transfer is not complete. This residual charge also affects the output of the next frame section _S1 . Therefore, normal output appears only in sections S ₂ and S ₃ . Among these, the signal of section _S2 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 FIG.
Shown in b. The reason why approximately T is used here is that, as shown in FIGS. 4a and 4b, the scanning signal pulse and the clock pulse are not synchronized, so the value will be between T and T+ _T0 . The reason why there are two sections giving the same normal output level, such as sections S ₂ and S ₃ , is that the section length is made considerably smaller than the scanning period.
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 drawings]

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. 4 is a diagram showing the sensitivity characteristics of a photodiode. 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. DESCRIPTION OF SYMBOLS 1... Light receiving section, 2... Gate section, 3... Charge transfer section, 4... Control signal input terminal, 5... Clock pulse input terminal, 6... Charge transfer section output terminal, 7
... Clock pulse generation circuit, 8 ... Count circuit, 9 ... Section selection circuit, 10 ... Analog switch, 11 ... Scanning signal input terminal, 12 ... Image sensor output terminal.

Claims (1)

[Claims] 1 In a one-dimensional image sensor consisting of a light receiving section, a gate section, and a charge transfer section, there are two terminals to which a scanning signal and a clock pulse are input, and a fixed number of the clock pulses input when the scanning signal is input and thereafter. and a counting circuit that generates one pulse for each predetermined section within the scanning signal period when counting is performed, and the gate section is controlled by the output of the counter circuit, and the pulse generated at the light receiving section is controlled by the output of the counter circuit. The charges are transferred in parallel to the charge transfer section, and the charges are sequentially transferred by the clock pulses and output in series from the output terminal, and the period is divided by the output pulses of the counter within the scanning signal period, An image sensor that passes only the output of the charge transfer section for one section not adjacent to the scanning signal and uses it as an output signal.