JPS6220479A - Driving device for image sensor - Google Patents

Abstract

PURPOSE:To cancel crosstalk generated at the signal output terminal of an analog switch by providing a means which inverts and differentiates a clock signal, adjusts its waveform, and superposing the resulting signal upon the signal input terminal as compensating pulses. CONSTITUTION:When the control clock signal CK of the analog switch 4 goes up to a high level, the output of an image sensor is read up. At this time, when the clock signal CK rises or falls, the analog switch 14 generates crosstalk in the differentiated shape of the clock signal. The inverted signal, the inverse of CK of the clock signal CK, on the other hand, is differentiated and shaped by compensating pulse generating means 1 and 2 and superposed upon the signal input terminal of the analog switch as compensating pulses. Consequently, the crosstalk generated by the analog switch 4 is in the same shape with the compensating pulses and different in polarity, so they cancel each other and a signal output having no crosstalk is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention solves crosstalk generated in an image sensor driving device that selectively reads image sensor output using an analog switch according to a predetermined clock signal. This is an image sensor driving device in which a signal obtained by differentiating a signal is superimposed on a signal input terminal of the analog switch to cancel the signal.

[Industrial application field]

The present invention relates to an image sensor driving device using an analog switch that can cancel crosstalk.

[Conventional technology]

Image sensors using COD and photodiodes are
By arranging a large number of each element in a lattice pattern and reading out the output signals from each element in a high-speed, periodic time-sharing manner, it is possible to provide an excellent function as an image sensor, which is attracting attention. In this case, a driving device is required to selectively read output signals from each element. As such a driving device, an analog switch using a gate such as an FET, which is easy to control and low cost, is usually used. This turns on the analog switch by inputting a clock signal to the control input terminal of the analog switch.This allows the output signal from the image sensor that is input to the signal input terminal to be time-divided from the signal output terminal. is selectively read out.

However, the above-mentioned analog switch generates crosstalk noise of 0 to several hundred mV at the signal output terminal when the clock signal, which is its control input, rises or falls. This is because the capacitance inside the analog switch generates crosstalk noise as a signal obtained by differentiating the clock signal. Since this crosstalk noise differs in magnitude from element to element and is larger than the output of the image sensor (0 to several tens of mV), a technique for canceling it is required.

[Problem that the invention seeks to solve]

In order to cancel the crosstalk noise, conventionally, gates for both N and P channels are used as analog switches, and crosstalk signals having opposite phase characteristics are input to the two gates, thereby canceling out the mutually occurring crosstalk. was.

But even with analog switches like this.

It is difficult to completely cancel out crosstalk noise, and furthermore, the remaining crosstalk noise has large variations between elements, making adjustment difficult.

In order to eliminate the above-mentioned problems, the present invention has a means for inverting and differentiating the black signal, adjusting its waveform, and superimposing it on the signal input terminal of the analog switch as a compensation pulse, thereby outputting the signal. An object of the present invention is to provide an image sensor driving device that can cancel out crosstalk occurring at terminals.

[Means for solving problems]

In order to solve the above problems, the present invention inputs a predetermined clock signal (CK) to a control input terminal, inputs an image sensor output to a signal input terminal, and outputs a signal from the image sensor according to the clock signal (CK). An analog switch (4) that selectively reads data from an output terminal, and an analog switch (4) that uses the clock signal (CK) by differentiating an inverted signal (X) of the clock signal (CK). Compensation pulse generation means (1) generates a compensation pulse to cancel the generated crosstalk and superimposes it into the signal input terminal of the analog switch (4).
, 2).

[For production]

In the above means, as shown in FIG. 1, a clock signal (C
When K) reaches a high level.

The output of the image sensor input to the signal input terminal is read out from the signal output terminal. At this time, the analog switch (
In 4), the rise of the clock signal (CK),
Or, at the time of falling, crosstalk occurs in a differentiated form. on the other hand.

The inverted signal (]) of the clock signal (CK) is differentiated and shaped by the compensation pulse generating means (L2) and superimposed on the signal input terminal of the analog switch notch (4) as a compensation pulse. Thereby, the crosstalk generated in the analog switch (4) and the compensation pulse have the same shape and opposite polarity, so they cancel each other out, and a signal output without crosstalk can be obtained.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail.

(Configuration of First Embodiment (FIG. 1)) FIG. 1 is a configuration diagram of a first embodiment of the present invention. 1st
In the figure, the first terminal of the photodiode 5 is connected to the ground via the bias power supply 6, and the second terminal is connected to the signal input terminal of the analog switch 4.

A signal output terminal of the analog switch 4 is connected to a load resistor 7 whose one terminal is connected to ground 11, and is also connected to an output terminal 10 via an amplifier 8. on the other hand.

Input terminal 9 is connected to a control input terminal of analog switch 4 via inverter 3 and to a first fixed terminal of variable resistor 2 . A second fixed terminal of variable resistor 2 is connected to ground 11.

Similarly, the variable output terminal is connected to the first terminal of the variable capacitor 1. The second terminal of the variable capacitor 1 is connected to the signal input terminal of the analog switch 4 in a superimposed manner.

(Operation of the first embodiment (FIGS. 1 and 2)) The operation of the embodiment having the above configuration will be explained using the operation shown in FIG. 2 and using the imaging chart 1. First, the inverted clock signal CK is input to the input terminal 9, and its waveform at point A is as shown in FIG. 2(a). Next, this signal is inverted by the inverter 3 and inputted to the control input terminal of the analog switch 4 as the clock signal GK. The waveform at point B is as shown in Fig. 2 fb). On the other hand, when light hits the photodiode 5, a waveform shown in FIG. 2 (C1) is obtained at point D as an output waveform. This signal is.

Since the analog switch 4 is turned on when the input signal CK is at a high level, an output appears at the signal output terminal, and the amplifier 8
After being amplified, the signal is output from the output terminal 10.

Here, within the analog switch 4, losstalk occurs as shown in FIG. 2 fdl when the clock signal CK is differentiated. This occurs due to the capacitance within the analog switch 4. Therefore.

If there is no variable capacitor 1 and variable resistor 2, the output waveforms are the photodiode output in Figure 2 (C) and the output waveform in Figure 2 f.
The crosstalk of d) overlaps, resulting in a waveform as shown in FIG. 2(e), which is directly amplified by the amplifier circuit 8 and output from the output terminal lo.

The output of the photodiode 5 will not be reflected correctly.

Therefore, in order to cancel the above crosstalk.

A differential waveform 1 of the clock signal CK, that is, a compensation pulse having characteristics opposite to crosstalk is generated. For this purpose, the inverted clock signal CK shown in FIG. 2(a) is differentiated by the combination of the variable resistor 2 and the variable capacitor 1. By adjusting their resistance and capacitance values, a compensation pulse having the same shape and opposite polarity as the crosstalk is generated. The waveform at the 0 point is as shown in FIG. 2(f).

By superimposing this compensation pulse on the signal input terminal of the analog switch 4, it cancels out the crosstalk of di generated in the analog switch 4.

As shown in Figure 2 1g)), the output at point E is the second
The output of the photodiode 5 in Figure (C) can be read out faithfully.

As mentioned above, variable capacitance 1. Variable resistance 2. By simply adding the inverter 3 and the inverter 3, the output of the photodiode 5 without crosstalk can be read out in accordance with the clock signal CK by simple adjustment.

(Configuration of Second Embodiment (FIG. 3)) Next, FIG. 3 shows the configuration of a second embodiment of the present invention. FIG. 3 shows the embodiment of FIG. 1 applied to a matrix reading type photodiode array, and shows a set BD of nxm[l diode arrays.

It is composed of PD. Gui Auto Array BD for every n pieces
K, PDK1~BDKh, PDKn (K=1.2°...
. Each diode array B DK, PDK1 to B DKn,
The outputs of the PDKn are selectively read out from the output terminals 15 via the reading circuits 14 by respective analog switches IK. The analog switch (2) is turned on by a clock signal iK obtained by inverting the inverted clock signal from the shift register 13 by each inverter TK. The crosstalk at this time is compensated by each variable resistor RK and variable capacitor CK.

(Operation of Second Embodiment (FIGS. 3 and 4)) The operation of the above-described configuration will be described next.

First, the clock signal S1 from the shift register 12 is set to high level, the analog switch S1 is closed, and the inverted clock signal i+ from the shift register 13 is set to low level.

Turn on ■1. As a result, the photodiode P
The output of D1+ is read by the reading circuit 14. next,
T] is set to high level, l] to i are sequentially set to low level, and analog switches I2 to I are sequentially turned on to read the output of each photodiode PD12 to PDPn. At this time, crosstalk in each analog switch 11-In is canceled by a compensation pulse generated by each variable resistor R1-Rn and each variable capacitor C1-Cn. These have been optimally adjusted in advance. Subsequently, the analog switch S1 is turned off, and 32
~S In, each photodiode P
D21- PD2n, ...

The outputs of PD□1 to PD, rln are read sequentially. In addition.

The crosstalk of the analog switches S1-S is not so great that no compensation is required for it.

Figure 4 (al) and (b) show the output waveforms before and after compensation when m = 30° and n = 32 in Figure 3. Figure 4 shows the output with each photodiode shielded from light. Therefore, the output of fa) in the figure directly corresponds to the crosstalk of the analog switches 11 to TIN. By performing compensation, the crosstalk was reduced as shown in the figure (bl).The noise at this time was about 1QmV, which was about 1150 compared to the photodiode's optical output of about 500mV.

It has become possible to lower the level to a level that poses no problem in practice.

〔Effect of the invention〕

According to the present invention, by simply adding an inverter, a variable capacitor, and a variable resistor to each analog switch.

By simple adjustment, it is possible to provide an image sensor driving device that can cancel crosstalk.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention. FIG. 2 is an operation timing chart of the first embodiment of the present invention. FIG. 3 is a configuration diagram of a second embodiment of the present invention. FIG. 4 is an explanatory diagram of the operation results of the second embodiment of the present invention. 1.01~Cn...variable capacitance. 2. R1~R,...variable resistance. 3. T1 to Tn...inverter. 4.■1~In...Analog switch. Figure 1 (C) in the 5th book (D) of the structure of Akira Kikin's rod 1 (D) Ri-h yard diagram 2

Claims (2)

[Claims] (1) Analog that inputs a predetermined clock signal (CK) to the control input terminal, inputs the image sensor output to the signal input terminal, and selectively reads the image sensor output from the signal output terminal according to the clock signal (CK). The switch (4) generates a compensation pulse that cancels the crosstalk generated in the analog switch (4) by the clock signal (CK) by differentiating an inverted signal (@CK@) of the clock signal (CK). A driving device for an image sensor, comprising compensation pulse generating means (1, 2) for superimposing input into a signal input terminal of the analog switch (4). (2) The compensation pulse generating means (1, 2, 3) has a variable resistor (2) and a variable capacitor (1) as a constituent circuit, and the inverted signal (@CK@) of the clock signal (CK) is generated by the variable resistor (2) and the variable capacitor (1). (2), the second fixed terminal is also grounded, and the first terminal of the variable capacitor (1) is connected to the variable output terminal, and the variable capacitor (1) The second terminal of the analog switch (4) is connected to the signal input terminal of the analog switch (4), and the second terminal of the variable capacitor (1) and the variable resistor (2) is connected to the signal input terminal of the analog switch (4).
) to generate a compensation pulse as an output of the second terminal of the variable capacitor (1) that cancels the crosstalk generated in the analog switch (4) by the clock signal (CK). An image sensor driving device according to claim 1.