JPH02183662A - Picture reader - Google Patents

Abstract

PURPOSE:To cancel noise by outputting a drive signal given to a MOSFET switch from a shift register while arranging a trailing timing of the signal and a leading timing of the succeeding signal. CONSTITUTION:When a signal from a shift register 8 is applied to a MOSFET switch 3 to output a picture signal from photosensors 1a-1n switchingly, the trailing timing of the n-th output of the shift register 8 and the leading timing of the (n+1)th output are made coincident. That is, the timings of signal waveforms outputted from terminals Q1-Qn of the shift register 8 are arranged so as to cancel the trailing of n waveform Q1 and the leading of the waveform Q2, and similarly, to cancel the trailing of the preceding waveform and the leading of the succeeding waveform. Thus, noise generated from the MOSFET switch 3 to an output line 4 is cancelled together.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reading device such as an image sensor including a solid type and a line type.

[Conventional technology]

In conventional image sensors, MOSFETs are used as switches to select the output from each photosensor.
However, noise was generated when the MOSFET was turned on, and the noise had an adverse effect on the image.

Traditional methods to cancel this noise include;

There were two things:

i) Use both P-channel and N-channel switches for MOSFET switches so that the two noises from each of these switches, or the three noises from the input circuit in addition to these, cancel each other out. do.

ii) Use a special noise prevention circuit for each MO3FET switch.

[Problem to be solved by the invention]

However, among the above methods, method i) (
b) Both P-channel and N-channel MO8FETs are required, and P-channel and N-channel MOS FETs are required.
It is not possible to freely set the transistor size (both W and L) of each transistor. (b) It is extremely difficult to set the operating timings of the switches of both MOSFETs so that both noises cancel each other out.

(c) If settings are made to cancel out the noise of the three above, when reading out the output from the other photosensors, only the first one will differ in conditions such as circuitry and timing.
Negatively affects other properties.

Furthermore, in the method ii) above, (a) the circuit becomes extremely complex and the number of circuit elements increases. There was a problem.

The purpose of the present invention is to solve these conventional problems.

To provide an image reading device capable of canceling out noise with a simple circuit without adding any special elements.

[Means to solve the problem]

To achieve the above object, an image reading device of the present invention includes a photosensor for reading an image, an MO8FET switch that sequentially switches output from the photosensor, and a shift register that drives the MO8FET switch. In the reading device, a drive signal applied from the shift register to the MO3FET switch is outputted so that the falling timing of the nth (n≧2) MO8FET switch and the rising timing of the (n+1)th MO3FET switch are aligned. It is characterized by the fact that it is made as follows. Also, a capacitor connected to an output line that takes out the output from the photosensor, an input circuit that gives a start signal to the shift register, and an MO5FET that is started by the start signal and is switched first.
Another feature is that a cancellation signal application circuit is provided which outputs a cancellation signal to the output line through the capacitor in synchronization with the rising timing of the switch.

[For production]

In the present invention, (i) when applying the signal from the shift register to the MO3FET switch to switch and output the image signal from the photosensor, the falling timing of the nth output of the shift register and the (n+1)th By matching the rise timings of the outputs, noise generated when the switch is turned on is canceled out. (ii) Furthermore, in one reading sequence, when reading the output from the first selected photosensor, a signal is output from the cancellation signal application circuit through the capacitor connected to the output line, and the rise timing of the first output is By matching the falling timing of the cancellation signal with the falling timing of the cancellation signal, the noise generated when the first switch is turned on is also canceled. Thereby, the S/N ratio with respect to the output of the photosensor can be significantly improved. Also, N-channel MO5FET
By using only switches, the device configuration including the shift register can be simplified. Also, N
When configuring a channel and a P channel as a set, the sizes of both switches can be set independently of each other, so the degree of freedom in design is great.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram of an image reading apparatus showing a first embodiment of the present invention, and FIG. 2 is an operation timing chart in FIG. 1.

In Fig. 1, 1a, 1b, 1c, ... 1n are photosensors, 3 is an N-channel MO5FET switch (S
c-engineering, 5ch2, 5ch3. ...5ch),
4 is the output line connected to the drain side of MO3FET switch 3, 8 is Q + Q 2 + Q 3...
This is a shift register that sequentially outputs clock signals to the Qn terminal.

In this embodiment, as shown in FIG. 2 (A), (B), and (C), the terminals Q,,Q,,Q,...
By aligning the timing of the signal waveforms output from Qn, the falling part of the waveform Q and the rising part of the waveform Q2 cancel each other out.

Falling waveform Q2 and waveform Q.

Similarly, the falling edge of the previous waveform and the rising edge of the subsequent waveform cancel each other out.

In this way, the MOSFEs turned on after 5ch2
Noises generated from the T-switch to the output line cancel each other out.

In FIG. 1, shift register 8 is started by first inputting a start signal to shift register 8. As shown in FIG. As a result, Qz+Q of shift register 8
3t...Pulses are sent out from the Qn terminal at regular intervals (see (A), (B), and (C) in Figure 2).
, applied to the gate of each MOSFET switch. As a result, the photosensors la, lb, lc, . . . 1n
The signal voltage received and photoelectrically converted is output to the output line 4 under control of the gate voltage. The pulse voltage appearing on the output line 4 is applied to the photosensors 1a, 1b, 1
The value is proportional to the amount of light received at c, . . . 1n.

In addition, in this example, since only the N-channel MOSFET switch is used, including the shift register 8,
This can be achieved with a very simple configuration.

In the case of a monolithic configuration, the chip size becomes extremely small.

FIG. 3 is a configuration diagram of an image reading apparatus showing a second embodiment of the present invention, and FIG. 4 is an operation timing chart in FIG. 3.

In FIG. 3, the difference from FIG. 1 is that the photosensor 1
a, 1b, 1c, . . . and a current amplifier (BuF 1 ) between each MOSFET switch 3.

BuF2. Buf3. ...) 11 is provided, and the 1M08FET switch 3 is replaced with an N-channel MO3FET3.
It is constructed from a combination circuit of a and a P channel MOSFET 3b. In this case, Q of shift register 8,
Q2.・・・・・・Signal from Qn terminal to N channel MO
Applied to the transistor gate of the SFET switch, Q□
t Q 2 # Q 2 j...A signal from the Qn terminal is applied to the transistor gate of the P-channel MO5FET switch.

In this example, Fig. 4 (A) (B) (C) (D) (E)
As shown in (F), by aligning the timing of the output waveforms from the shift register 8, the noises generated in the output line 4 from the MOSFET switches turned on after the MOSFET switch (S ch, ) are canceled out. In addition, in FIG. 4, the timing when Q n (n≧1) becomes H level (or L level) and Q n (
There is no need to align the timing at which n≧1) becomes L level (H level) in order to cancel noise; in other words, since this is the end of the operation, the image is not affected. In addition, in this embodiment, the sizes of the N-channel MOSFET switch and the P-channel MO5FET switch can be set independently of the size of the switch, so there is a large degree of freedom in design, and it is therefore possible to create a high-performance image reading device. . In addition, in the embodiments shown in FIGS. 1 and 3, 1M0
The coupling capacitance between the gate of the 8FET switch and the output line 4 is set to the same polarity (N channel and N channel, P channel and P
The MOSFETs of each channel must be the same.

In this way, in the embodiments shown in FIGS. 1 and 3, when the n-th (n≧2) MOSFET switch is turned on, noise is generated in the output line 4. The S/N of the image reading device is
The outputs from the second and later selected photosensors 18 to 1n are significantly improved. In particular, it is very effective for outputs at dark levels and at low levels of light. With such a configuration, a multi-gradation image reading device can be easily realized.

Note that there is no problem even if both the P channel and the N channel are used in the MOSFET switch, or even if only the P channel or only the N channel is used. When both P-channel and N-channel are used, the transistor sizes can be freely set separately.

FIG. 5 is a configuration diagram of an image reading apparatus showing a third embodiment of the present invention, and FIG. 6 is an operation timing chart in FIG. 1.

In FIG. 5, 1a, 1b, and 1c are photosensors, and 3 is an N-channel MOSFET switch (Schl).

Sah2. S ah, ), 2 is a capacitor S cho using the same shape as the MO3FET switch, and is a capacitor for applying a cancellation signal, 4 is an output line connected to the drain side of the MO3FET switch 3, and 5 is an output load capacitor.

6 is the output reset switch (N-channel MO3FET)
, 7 is a cancellation signal application circuit, 8 is a shift register that sequentially outputs clock signals to terminals Q□, Q2°Q, and 9 is an input circuit that inputs a start signal.

In this embodiment, as shown in FIGS. 6A, 6B, and 6C, terminals Q, , Q2 . Q.

By aligning the timings of the signal waveforms output from . . . , the falling portion of the waveform Q1 and the rising portion of the waveform Q2 cancel each other out. The falling edge of waveform Q2 and the rising edge of waveform Q3 cancel each other out, and similarly, the falling edge of the previous waveform and the rising edge of the subsequent waveform cancel each other out. As shown in FIG. 6 (D), at the same timing as the rise of the Q□ waveform, a negative pulse is applied from the cancellation signal application circuit 7 to the MO3FE.
By applying it to the gate of the T switch Sah, the falling edge of this pulse and the rising edge of the Q1 waveform cancel each other out. In this way, MO turned on after 5ch2
Noise generated on the output line from the 3FET switch cancels each other out. In this way, in this embodiment, capacitor 2 is connected to the output line, and these capacitors 2
A cancellation signal is applied from the shift register 8 and the cancellation signal application circuit 7 through the circuit.

In FIG. 5, first, by inputting a start signal from the start signal input circuit 9 to the cancellation signal application circuit 7 and the shift register 8, both circuits 7 and 8 are activated. At the same time, the clock signal CLK is also applied to the cancellation signal application circuit 7.
is input to the shift register 8 (see CLK in FIG. 6). As a result, the QO terminal of the cancellation signal applying circuit 7 and the Q 11 QZ I Q3 # of the shift register 8
...Pulses are sent out from the terminals at regular intervals (see (D), (A), (B), and (C) in Figure 6).
, applied to the gate of each MOS FET switch. As a result, the photosensors la, lb, lc,
The signal voltage received and photoelectrically converted is output to the output line 4 under the control of the gate voltage (see the output waveform in FIG. 6). The pulse voltage appearing on the output line 4 has a value proportional to the amount of light received by the photosensors la, lb, lc, . . . .

In addition, in this example, since only the N-channel MOSFET switch is used, including the shift register 8,
This can be achieved with a very simple configuration.

In the case of a monolithic configuration, the chip size becomes extremely small.

In the embodiment shown in FIG. 5, the capacitor 2 has the same shape Sch as the MO5FET switch. Further, in this reading device, the output is read when the clock CLK is at the L level, so that the noise caused by the switching shown in FIG. 6(D) does not have an adverse effect. Further, in this circuit, noise when the start signal input circuit 9 operates is ignored.

FIG. 7 is a configuration diagram of an image reading device showing a fourth embodiment of the present invention.

In FIG. 7, the difference from the configuration in FIG. 5 is that the photosensors 1a, 1b, 1c... and the MO8FET switch 3
Between the current amplifiers (BuF 1 , BuF 2 ).

BuF3...) 11 is provided, and the capacitor 10 for applying the cancellation signal is appropriately set. That is, the current value flowing through the switch 3 is increased by the current amplifier 11, and the N-channel MO
The capacitor 2, which had the shape of an 8FET, is now an independent capacitor 1o connected to the output line 4. As a result, the nth and (n + 1
)th noise can be canceled out.

In this manner, in the embodiments shown in FIGS. 5 and 7, the S/N ratio for the output of the photosensor selected first in the reading sequence of the image reading device is significantly improved.

Furthermore, since the configuration is very simple, a multi-gradation image reading device can be easily realized. Furthermore, P channel and N
In the case of a combination of channels, the transistor size can be freely set for each of the P channel and N channel.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to cancel the noise generated when the output selection switch from the photosensor is turned on with a simple circuit without adding any special elements to the conventional circuit. .

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an image reading device showing a first embodiment of the present invention, FIG. 2 is an operation timing chart in FIG. 1, and FIG. 3 is an image reading device showing a second embodiment of the present invention. 4 is an operation timing chart in FIG. 3, FIG. 5 is a configuration diagram of an image reading device showing a third embodiment of the present invention, and FIG. 6 is an operation timing chart in FIG. FIG. 7 is a configuration diagram of an image reading device showing a fourth embodiment of the present invention. la~In: Photosensor, 2: Capacitance, 3: MO8FE
T switch, 4: Output line, 5: Output load capacity, 6:
Output reset switch, 7: Cancellation signal application circuit, 8
:Shift register, 9-star signal input circuit, 1o:
Capacitor for applying a cancellation signal, 11: Current amplifier.

Claims (2)

[Claims] (1) In an image reading device comprising a photosensor for reading an image, a MOSFET switch that sequentially switches the output from the photosensor, and a shift register that drives the MOSFET switch, the shift register is connected to the MOSFET switch. An image reading device characterized in that a drive signal to be applied is outputted so that the falling timing of an n-th (n≧2) MOSFET switch and the rising timing of an (n+1)-th MOSFET switch are aligned. (2) The image reading device according to claim 1, further comprising: a capacitor connected to an output line for taking out the output from the photosensor; and an input circuit for giving a start signal to the shift register; An image reading device comprising: a cancellation signal applying circuit that outputs a cancellation signal to the output line through the capacitor in synchronization with the rising timing of a MOSFET switch that switches to the output line.