JPS61284176A - Picture signal amplifying circuit - Google Patents

Abstract

PURPOSE:To prevent a reference level from being changed with the quantity of incident light by separating an outputting a picture read signal by a differential amplifier after the output signal of a linear image sensor and a compensating signal have levels shifted. CONSTITUTION:A CCD line sensor 1 converts photoelectrically the quantity of light incident on each of cells arranged on, for example, a line and outputs an output signal including a driving signal and the picture read signal and the compensating signal consisting of a signal other than the picture read signal to output terminals 1-1 and 1-2 respectively. The signal outputted from the terminal 1-1 is supplied to a transistor (TR) 1 through a resistance R1 and has the DC level shifted and is applied to an inverted input 2-1 of a differential amplifier 2. The signal outputted from the terminal 1-2 is supplied to a TR 2 through a resistance R2 and has the level shifted similarly and is applied to a non-inverted input of the amplifier 2. The amplifier 2 separates and outputs the picture read signal, thereby preventing the reference level from being changed with the quantity of incident light.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image reading device that reads an image by photoelectric conversion and outputs an image reading signal, and particularly relates to an image reading device that reads an image by photoelectric conversion and outputs an image reading signal. The present invention relates to an image signal amplification circuit that separates and outputs an image signal.

[Prior art and problems]

A COD (charge coupled device) line sensor is, for example, a photoelectric conversion element that sequentially outputs a voltage corresponding to the amount of light incident on each cell arranged in a straight line as a serial signal in accordance with an input signal. This CCD
Line sensors output such serial signals, so the number of bits in the output signal line is much smaller than the number of cells.
Furthermore, since there is no need for a selection circuit to select each cell,
It is used as a sensor for image reading in various fields.

-a, the CCD line sensor has a control terminal to which driving pulse signals such as clock pulses, shift pulses, and reset pulses are applied, and an output signal terminal to which the induced component of the reset pulse and the image reading signal are superimposed and output. , and a compensation signal terminal that outputs a compensation signal for separating only the image reading signal from the output signal. A reset pulse is induced for each pixel output signal and applied to each element, and signals such as these induced components are simultaneously output from the output signal terminal mentioned above in addition to the image reading signal. This is a reference signal for separation.

FIG. 2 is a waveform diagram showing the signal output from the output signal terminal. The shaded area represents the area or envelope of the signal. A guidance signal (A) corresponding to the reset pulse signal is output. Then, during the one-line output period T, an image reading signal corresponding to the amount of incident light is superimposed on the signal (A) and output (B). Further, the output signals (A) and (B) include a bias voltage (6 to 9 V) to be applied to each cell. The portion indicated by A in FIG. 2 is an enlarged view of the output signal waveform during one line output period T.

An output signal waveform is formed by an image reading signal S below the bias voltage (6 to 9 V), ie, in the direction of the low voltage section, and a reset pulse induction signal R, indicated by the dotted line, above the bias voltage, ie, in the direction of the high voltage section.

The required signal among the output signals of the COD line sensor is the image reading signal S, and it is not necessary to separate only the image reading signal S from this output signal. Conventionally, only the image reading signal mentioned above has been separated. A circuit as shown in Fig. 3 was used for the output circuit.Each signal output from the output terminal 1-1° compensation signal terminal 1-2 of the CCD line sensor 1 is connected to the resistor ROII RO21RO3, R[141] It is added to two emitter follower circuits consisting of transistors Tro+ and Tro2. The outputs thereof, that is, the emitter outputs of transistors Tro + and TRo 2, were applied to the video amplifier 2 via capacitors CI and C2, respectively. This emitter follower amplifier circuit operates as an impedance conversion circuit. Then, the bias voltage is cut by the capacitors CI and C2, and the signal of the induced component such as the above-mentioned reset pulse superimposed by the video amplifier 2 is subtracted and outputted from the output terminal.

FIGS. 4(al) and 4(C) show the areas or envelopes (shaded areas) of the respective output signals and compensation signals output from the CCD sensor 1. FIG.

FIGS. 4(b) and 4(d) show the envelopes of the signals applied to the outputs of the emitter follower, that is, the inputs 2-1, 2-2 of the differential amplifier 2 which operates as a video amplifier. Figures 4 (b) and (d) show that although the DC component (approximately 6 V) is almost cut off by the capacitor, when two images are input, the Ov level of the output signal changes in response to the signal change in the negative direction. changes (in Figure 4))
. In other words, since the waveform of the output signal changes only in the negative direction, the average DC level changes in one cycle depending on the image level, and the DC component cannot be completely removed due to the effect of charging and discharging the capacitor. The output signal O■
The level changes. When such a signal is applied to a differential amplifier, it is possible to output an image reading signal by means of a compensation signal, but a problem arises in that the Ov level changes depending on the level of one image reading signal. Conventionally, when the output of the differential amplifier 2 mentioned above is binarized into black and white data, the fifth
A specific level (darkness value) as shown in Figure (a), for example -
〇, when it is 1V or more, it is determined as a black level, and when it is less than -0, 1V, it is determined as a white level. However, since the standard of the one-image reading signal is deviated from the O level as described above, the white level of the halftone image is quite close to this darkness value. For example, when reading a newspaper or the like, there is a problem in that since one sheet of paper is not completely white, the input is determined to be entirely black. In addition, the image reading signal mentioned above includes shading distortion in which the level at the reading start and end ends decreases, so even if the entire area is white as shown in Figure 5(b), the reading signal There was a problem in that the starting end and ending end portions exceeded the darkness value level, and were determined to be black levels even though they were white levels.

[Purpose of the invention]

The present invention solves the above problem, and its purpose is to output approximately OV when it is black (when no light is incident), and to output approximately OV when it is white (when light is incident). The reference level is fixed so that it changes in the positive or negative direction from Ov, and circuits such as DC regeneration and DC clamp are not required, and the timing circuit for capturing the image reading signal is simplified. An object of the present invention is to provide an image signal amplification circuit that enables cost reduction.

[Key points of the invention]

The present invention is characterized by a linear image sensor that performs photoelectric conversion and outputs an output signal including a driving signal and an image reading signal, and a compensation signal consisting of a signal other than the image reading signal; a first level shift circuit to which the compensation signal is applied, a second level shift circuit to which the compensation signal is applied, and a differential amplifier that differentially amplifies the output of the first to second level shift circuit; The image signal amplification circuit is characterized in that after level-shifting the output signal of the linear image sensor and the compensation signal, the differential amplifier separates and outputs an image reading signal.

The effect is as described below.

An output signal including a drive signal and an image reading signal output from a linear sensor that performs photoelectric conversion.

and a compensation signal for separating the image reading signal from the output signal. Add to the second level shift circuit.

And the first. The second level shift circuit independently removes the DC level and outputs a signal with a fixed O■ level. Then, these two signals are added to the differential amplifier 2 to obtain a difference value and output a 9-image reading number multiple.

[Embodiments of the invention]

The present invention will be described in detail below using one embodiment of the present invention.

FIG. 1 is a circuit diagram of an embodiment of the present invention.

In addition, CCD line sensor 1. The differential amplifier 2 is similar to that in the conventional circuit shown in FIG.

Note that the control circuit is not directly related to the present invention.

It is omitted in FIG. 3. The emitter of the transistor Trs is connected to the power source -6°. Since the base and collector of the transistor Tra are connected to the power supply VCC via the variable resistor R5, the current flowing between the collector and emitter of the transistor Tra is approximately determined by the variable resistor R5 and the power supply VCCICC-6.

On the other hand, the base of the transistor Trs and the transistor Tr
It is connected to the base of transistor T.
The emitter of r3 is connected to the power supply -■, like the emitter of the transistor Tra.

A current having the same value as the base current appearing in the transistor Trs flows to the base of the transistor Tr3,
The collector-emitter current of r3 is constant. This operation causes the transistor Tr3 to operate at a constant current.

On the other hand, the output signal output from the output terminal 1-1 of the CCD line sensor 1 is applied to the base of the transistor Tr+ via the current limiting resistor R+. The collector of transistor Tr+ is connected to power supply vcc. The emitter is connected to the collector of the transistor Tr3 via a resistor R3.

As mentioned above, the transistor Tr3 is the transistor Tra.
Since the transistor Tr3 is configured so that the same current flows therethrough, the transistor Tr3 operates as a constant current load when the transistor Tr+ operates as an emitter follower. Due to the constant current operation of the transistor Trz, the current flowing through the transistor Tr+ and the resistor R3 becomes constant, and a constant DC voltage is always applied to both ends of the resistor R3. Since the transistor Tr+ operates as an emitter follower as described above, the voltage at the emitter of the transistor Tr+ is lower than the input voltage by the junction voltage between the base and emitter of the transistor Tr+.

These operations cause the collector of the transistor Tr3 to rise even further than the emitter voltage of the transistor Tr+.
The voltage is lowered by the voltage generated in . That is, CO
From the output signal output from the output terminal of the D line sensor, a voltage lowered by the base-emitter junction voltage of the transistor Tr+ and the voltage generated in the resistor R3 is transferred from the collector of the transistor Tr3 to the inverting input 2- of the differential amplifier 2. Join 1. In this way, a voltage obtained by shifting the DC level of the output signal of the CCD line sensor 1 is applied to the inverting input 2-1 of the differential amplifier 2.

FIG. 6(a) is a waveform diagram showing the output signal of the CCD line sensor 1. FIG. This signal is the transistor Tr mentioned above.
+, Tr 3. Tr5. Resistor R3 and variable resistor R
When added to the circuit consisting of 5, that is, the level shift circuit,
The output is a level-shifted signal with respect to the input (Figure 7 (
a)). The variable resistor R5 is varied so that the DC level of the output signal output from the CCD line sensor 1 is initially set to 0 level in the circuit described above.

On the other hand, the compensation signal output from the compensation signal terminal 1-2 of the CCD line sensor 1 is also level-shifted by the same circuit configuration as the circuit described above. That is, compensation signal terminal 1
-2 compensation signal connects the collector to the power supply Vc via the resistor R2.
It is added to the base of transistor Tr2 connected to c. The emitter of the transistor Tr2 is connected to the power supply -1, through a resistor R4 and a transistor Tri.

The emitter of the transistor Tra is the power supply -vl.

The collector is connected to the power supply vc through a variable resistor R6.
Since the transistor Tra is connected to the transistor Tra, a constant current flows through the transistor Tra. Since the base of the transistor Trs and the base of the transistor Tra are connected, the value of the current flowing to the base of the transistor Tr6 and the transistor T
It is equal to the current value flowing to the base of ra. As a result, the current flowing between the collector and emitter of the transistor Tri becomes constant and equal to the current value of the transistor Tr6, so the transistor T r a becomes a constant current load when the transistor Tr2 operates as an emitter follower. Due to the constant current operation of the transistor T r 2, the transistor Tr2. A constant current flows through the circuit connecting the power supply vcc and the power supply -711 through the resistor Rt and the transistor Tri.

A constant voltage is applied to resistor R4. Further, at the emitter of the transistor Tr2 operating as an emitter follower, a signal is generated in which the DC level of the compensation signal is lowered by the junction voltage between the base and emitter of the transistor Tr2.

Therefore, a compensation signal in which the junction voltage between the base and emitter of the transistor Tr2 and the voltage generated at the resistor R4 are lowered is output to the collector of the transistor Tr4, and is applied to the non-inverting input of the differential amplifier. Figure 6 (b
) is an envelope waveform diagram of the compensation signal output from the CCD line sensor 1. This signal is the transistor Tr2. By being applied to a level shift circuit consisting of Tra, a resistor Ra, and a variable resistor R6, its output becomes a signal (FIG. 7(b)) whose level is shifted relative to the input. still.

In this circuit as well, the variable resistor R6 is varied so that the DC level of the level-shifted compensation signal, that is, the signal applied to the non-inverting input of the differential amplifier 2, becomes O.

The differential amplifier 2 outputs the difference between the signal applied to its non-inverting input and the signal applied to its inverting input.

The image reading signal is separated from the output signal output from the CCD line sensor 1 and output. FIG. 8 shows an envelope waveform diagram of the image reading signal. In the embodiment of the present invention, the output signal of the CCD line sensor 1 is input to the inverting input of the differential amplifier 2.

Since the compensation signal is applied to the non-inverting input, one image reading signal is inverted and output from the differential amplifier 2.

No unnecessary DC level is generated in the image reading signal shown in Figure 8 due to the level shift, and when black (no light is incident) is read, it becomes almost Ov, and white (light is incident). The read level has a voltage value in the positive direction as the voltage increases.

In the embodiment of the present invention, the output signal of the CCD line sensor 1 is level-converted and applied to the inverting input of the differential amplifier 2, and the compensation signal is level-converted and applied to the non-inverting input, but the output signal is not limited to this. It is also possible to convert the compensation signal and input it to the non-inverting input, and then convert the level of the compensation signal and apply it to the inverting input. Incidentally, at this time, the output of the differential amplifier becomes an inverted version of the output waveform shown in FIG.

〔Effect of the invention〕

As described above, the present invention outputs approximately Ov when no light is incident on the CCD line sensor, and changes in the positive or negative direction from 0■ when light is incident, so that the reference level is adjusted depending on the amount of incident light. According to the present invention, it is possible to provide an image signal amplification circuit that does not require a circuit such as a DC clamp and has a simplified timing circuit. Therefore, according to the present invention, it is possible to provide an image signal amplification circuit with a simple configuration and low cost.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention. FIG. 2 is an output waveform diagram of the CCD line sensor. FIG. 3 is a circuit diagram of a conventional image signal amplification circuit. Figure 4 (al is an envelope waveform diagram of the output signal of the CCD line sensor. Figure 4 (bl is an input waveform diagram of the differential amplifier of the conventional circuit). Figure 4 (C) is the envelope waveform of the compensation signal of the CCD line sensor. Figure. Figure 4 (d) is an envelope waveform diagram of the compensation signal applied to the differential amplifier of the conventional circuit. Figures 5 (a) and (b) are the white level and black level when using the conventional image signal amplification circuit. Waveform diagram showing the relationship between level and dark value voltage. Figure 6 (al, (bl) is an envelope waveform diagram of the output signal and compensation signal applied to a conventional differential amplifier. Figure 7 (a) and (b) are Envelope waveform diagram of the output signal and compensation signal applied to the differential amplifier of the embodiment of the present invention. Fig. 8 is an envelope waveform diagram of the output of the embodiment of the present invention. l... CCD line sensor. Tr+ ~ Tra ... Transistor. R3, R4... Resistor. R5, Ra... Variable resistor. 2... Differential amplifier. Patent applicant Casio Computer Co., Ltd. Same as above
Casio Electronics Co., Ltd. Figure 2 Funeral Figure 3 (a) (b) Figure 6 Figure 7

Claims (1)

[Claims] a linear image sensor that performs photoelectric conversion and outputs an output signal including a driving signal and an image reading signal and a compensation signal consisting of a signal other than the image reading signal; and a first level shift circuit to which the output signal is added. , a second level shift circuit to which the compensation signal is added, and a differential amplifier that differentially amplifies the outputs of the first and second level shift circuits, the output signal of the linear image sensor and the compensation signal An image signal amplification circuit characterized in that after level-shifting the image reading signal, the differential amplifier separates and outputs the image reading signal.