JPS6091758A - Image sensor - Google Patents

Abstract

PURPOSE:To attain high speed reading by converting an external bit selection input signal into a multi-threshold logical signal of complementary output, and detecting optical information according to the said signal to form a sensor section and a scanning section on one chip. CONSTITUTION:The external input selection signal is inputted to an input terminal 1, compared with a reference voltage Vth by transistor (TR) pairs 4-6, and switched to positions (a), (b) depending on the result of comparison and complementary voltages with difference DC levels are generated from resistor pairs 7-9. The multi-threshold logical signal is inputted to an input terminal 14, led to desired photo TRs 32a-35a and 32b-35b by a current from a current source 16 controlled by a block selection input signal and the said logical signal is read. Since the TR pairs 4-6 and current switching TRs 17-19 are operated in the unsaturated state, high speed operation is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application With the advancement of information processing equipment such as computers, the importance of sensors as input devices is increasing. The present invention makes it possible to read information at high speed and with high accuracy by making full use of IC circuit technology.As conventional image sensors, first of all, Noricon Bisicon, MOS Target Vidicon, etc. can be mentioned, and these are successively developed. Since the access function for reading is performed by deflecting an electron beam, it has the advantage of being easy to read with high resolution, but since it is not entirely solid-state, it has drawbacks such as miniaturization and low power consumption.

On the other hand, examples of all-solid-state image sensors include COD image sensors and MOS image sensors.

Generally image-1! A sensor consists of multiple photodetecting elements and a scanning circuit, a COD image sensor uses a photodiode as a detection element and an ICD as a scanning circuit, and a MOS image sensor uses a photodiode as a detection element and a MOS shift register as a scanning circuit. I am using it. Both of these are M
Although the input sensor section and scanning circuit section are based on O8 integrated circuit technology and have high resolution, they also have the following drawbacks.

In the case of a COD image sensor, scanning can be done at high speed, but
Originally, charge carriers, which are in a thermally non-equilibrium state, are used for signal transfer, so they cannot be used at high temperatures. on the other hand,
In the case of a MOS image sensor, the resolution is still high, but the scanning speed is determined by the maximum clock frequency of the MOS shift register, and the limit is 0.3 μs/bit, and an additional circuit is required to reduce noise.

In recent years, contact image sensors have been actively developed in order to miniaturize and increase resolution of reading devices. - This requires a long image sensor corresponding to the width of the document, and thin film elements using CdS thin films and amorphous S1 are being developed, but they have low reliability, reading speed, 1 yield, and connection with the drive circuit. Many issues remain. On the other hand, COD
There have been attempts to lengthen MOS image sensors by arranging them in a staggered pattern, but in this case, problems arise with complete sealing of the package and cost as the size increases. Since this device uses Si surface channels, it is susceptible to external influences and requires a sufficiently airtight package with a transparent material to ensure reliability.

OBJECTS OF THE INVENTION An object of the present invention is to provide an image sensor in which a sensor section and a scanning section can be formed on the same chinobu, and which optically reads information at high speed, high sensitivity, and high resolution. The goal is to improve the reliability of the device itself and provide an image sensor that can guarantee reliability even in a simple package.

Structure of the Invention In order to achieve the above object, an image sensor of the present invention includes:
A multi-slep filter that converts the bit selection input signal from the external 7915 into a complementary output multi-thread 7 hold logic signal.
a current source controlled by a block selection input signal, a current switching circuit connected to a cascade path for causing the current from the current source to flow into a branch selected according to a multi-threshold signal, and a current switching circuit. It is composed of a phototransistor or a photodiode that senses the current of the circuit and turns on and off accordingly, and a phototransistor or photodiode that detects optical information based on the current of the PNP transistor.

In order to reduce the leakage of the input digital signal for selection to the output signal, the bit selection input signal is encoded with a Gray code, and the collector is set to the positive side to reduce the influence of the base-collector capacitance of the switch transistor (PNP) transistor. For the power supply, connect the emitter to the collector of the phototransistor,
Alternatively, it is characterized by being connected to the cathode of a photodiode.

Description of examples Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows the selection signal input terminal 1 of the input selection signal from the outside.
This is a circuit that converts this into multi-threshold logic with two complementary outputs. The current from constant current circuit 3 is
A pair of transistors 4, 5, . . .
According to the result of comparison with the logic reference voltage vth, the binary input selection signal 1 is switched to the transistor 4a or 4b side, the 5a or 5b side, and the 6a or 6b side by the respective currents. 7, 8.9, complementary voltages with different DC levels are generated.

For example, if the input terminal 1a of the bit selection input signal terminal 1 is
・When a level signal is input, complementary output 2 a becomes “I”.
H-', i becomes 'L'. This logical swing is determined by the value of the resistor pair 7 and the current value of the constant current circuit 3. 1, 10 to 12 are transistors for generating a DC level, and 13 is a resistor string for voltage division.

Although FIG. 1 shows the case of 3 bits, ), this can be extended to cases with a larger number of bits by repeating the same procedure.

FIG. 2 shows a circuit for receiving the aforementioned multi-threnohold logic signal at the input terminal 14, guiding the current from the current source 16 controlled by the block selection input signal to a desired phototransistor, and accessing this. It consists of cascade-connected current switching circuits. tiger 7ji 2
The pairs 17, 18, 19, . . . , 23 constitute a current switching circuit for switching the current flowing through the emitter pair of each transistor pair in accordance with a logic signal. Resistor 24a
.

24b...27a, 27b is a transistor pair 2°~
This is a load resistance that detects which of the 23 transistors are in a energized state. PNP) transistor 28a.

28b...31a, 31t) are transistor pair 2
Depending on the presence or absence of collector current of 0°21...23,
These are switching transistors that turn on or off, and their emitter electrodes are connected to phototransistors 32a and 32, respectively.
b ==-= connected to 35a, 35b. The emitters of the phototransistors are connected in common and this terminal 36
The voltage across the load resistor 37 provides a video output. Next, the specific operation will be explained. The block input terminal is “IH”
I+, when each of the bit selection input signals A, B, and C is "L", the current from the current source flows only through the resistor 24a,
It does not flow into other resistances. As a result, only the base potential of the PNP transistor 28& is lowered, and this transistor is turned "ON'", and a charging current flows only through the phototransistor 32a, so that the transistor 32a becomes a read state (access state). No current flows through the other phototransistors,
It becomes a floating state and becomes an integration period (non-access period).

If the logic amplitude of the input terminal 14 is 0.6 V, it is sufficient to drive the current switching circuit. High-speed reading is possible by operating the transistor in a non-saturated state.

Furthermore, in the present invention, switching PNP)/distor(
In order to reduce malfunctions due to the parasitic capacitance of the lateral PNP transistor (base of the PNP transistor and collector of the phototransistor), the emitter and collector connections are reversed, as shown in FIG. The structure of a lateral PNP transistor is shown in FIG. 38 is a base electrode, 3
9 is an emitter electrode, and 4Q is a collector electrode. Switching is performed at the base-collector junction, and current to the phototransistor is supplied from the emitter electrode. By connecting in this way, changes in base potential will not be directly induced to the collector of the phototransistor, and at the same time, since the area of the emitter diffusion is originally smaller than the area of the collector diffusion, the change in the base potential will not be directly induced to the collector of the phototransistor. Malfunctions due to induction from the base to the collector of the phototransistor are eliminated.

FIG. 4 is a block diagram including a driving circuit for an image sensor according to the present invention. A flip-flop, an oscillator, and a counter are used to count up or down to the number of bits of the image sensor, and after converting the desired low color/color focus (corresponding to the number of bits of the bit selection input signal) to a gray code, the number of bits of the image sensor is A bit selection input signal is applied to terminal 1. This is applied as a shift clock to the shift register at a desired clock interval (corresponding to the number of bits in one block), and the output signal of the shift register is applied to the block selection input signal terminal 15 of the image sensor. This drive circuit allows sequential reading of video information.

Although the above description has been made regarding the case where a phototransistor is used as a photodetecting element, a photodiode can also be used in exactly the same manner.

Effects of the Invention As is clear from the above description, according to the present invention, a high-speed, high-sensitivity, and high-resolution image sensor can be realized. Further, all functions can be formed on a silicon chip using ordinary bipolar integrated circuit technology, and reliability is also good. Therefore, the present invention is extremely useful as an input device for information processing equipment, and has great industrial effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a multi-lens hold signal generation circuit in the image sensor of the present invention, FIG. 2 is a block diagram of a current switching circuit in the image sensor, and FIG. 3 is a plan view of a horizontal PNP transistor in the image sensor.
FIG. 4 is a block diagram of the entire image sensor including the drive circuit. 1... Selection signal input terminal, 2... Multi-slend hold signal input/output terminal, 3... Constant current circuit, 4゜5.6
...Transistor pair for current switch, 7°8.9・
... Resistor pair, 10.11.12 ... Transistor pair for DC level generation, 13 ... Resistor string for voltage division, 14 ... Input terminal, 15 ... Block selection input terminal, 16... Control current source, 17.1B
. 19120.21, 22.23... Current switching transistor pair +24 &, 24b ~ 27a', 27b
...Load resistance, 28a, 28b ~3+ a, 3
1 b...Switch transistor, 32a, 32
b~35a, 35b...Phototransistor, 3
6...Video output terminal, 37...Output load resistance,
38...Base electrode, 39...Emitter electrode,
4o...Collector electrode.

Claims (2)

[Claims] (1) A multi-threshold signal generation circuit that converts an external bit selection input signal into a complementary output multi-threshold logic signal and a current source controlled by a block selection manual signal are cascade-connected, and the A current switching circuit that receives a complementary output signal encoded with a Gray code from a multi-threno hold signal generation circuit and sends a current to a desired branch, and a resistor connected to each branch of this current switching circuit. , a PNP transistor that senses the voltage at the resistor end and performs a switch operation, and each PNP
) An image sensor comprising a phototransistor or a photodiode accessed by a current from a transistor, and obtaining a video output from the emitter terminals of the commonly connected phototransistors. (2) PNP that senses the voltage at the resistor end) The transistor is composed of a horizontal PNP transistor, with the collector electrode as the positive power supply terminal, the base electrode as one end of the resistor, and the emitter electrode as the collector of the phototransistor or photodiode. The image sensor according to claim 1, wherein the image sensor is connected to an anode.