JP2580809B2 - Image sensor circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a circuit relating to an image sensor used for an automatic focusing device of an optical instrument such as a camera, for example, and an image sensor comprising a charge storage type optical sensor. And an image sensor circuit including a circuit for handling the measurement data.

[Conventional technology]

In the image sensor used for the above-described automatic focusing device and the like,
You need to accurately measure the light intensity distribution in the image,
In addition, since the light intensity received by each of the optical sensors varies in a very wide range, it is advantageous to convert the light intensity into a charge storage time by making the optical sensor a charge storage type. For example, a photodiode is used in such a charge storage type optical sensor. That is, the junction capacitance of the photodiode is charged in a reverse bias state, discharged by a photocurrent corresponding to the light intensity received by the photodiode, and the time until the voltage across the junction capacitance changes by a certain value. Is the charge accumulation time.

After the light intensity is converted into the charge accumulation time by the charge accumulation type optical sensor in this way, the length of the charge accumulation time can be counted by an appropriate clock pulse, and each light in the image sensor can be counted by such means. The intensity of light received by the sensor can be represented by measurement data of a desired number of bits, for example, 8-bit data. However, the number of stages of the light intensity, which may represent an 8-bit data whereas a 256, light intensity each photosensor is subjected may vary 1:10 ⁶ things within wide limits. Of course, the measurement data may be set to 20 bits, but it is not advantageous to increase the number of bits too much and has little practical significance.

In view of the above, conventionally, a means for converting the charge accumulation time into data by measuring pulses whose period changes with time has been used.
In other words, the light intensity that changes within a wide range as described above can be changed to a short measurement data within 8 bits by ticking the charge accumulation time with a measurement pulse whose period is usually gradually increased with time as a function of a preset measurement pulse. Thus, it can be expressed with practically accurate precision.

The function for specifying the variable period of the measurement pulse can be set in terms of circuits, but in order to be able to set the form of this function arbitrarily according to the application, it is necessary to store it in the form of a table in ROM. Is most desirable. The charge accumulation time of all the optical sensors in the image sensor is converted into data using the same measurement pulse. The measurement data obtained in this manner is temporarily stored in, for example, a latch for each optical sensor, and is read as needed.

The image sensor circuit including the above-described charge accumulation type image sensor and a circuit for converting the charge accumulation time into measurement data by using a variable period measurement pulse, all or main parts of the image sensor circuit are integrated together with related circuits in a semiconductor chip. Built into the optics for automatic focus adjustment.

[Problems to be solved by the invention]

However, such a conventional image sensor circuit has a problem that, when testing an integrated circuit device incorporating the same, the test result tends to be unclear and it is difficult to judge the quality.

In this test, an image or a uniform light of a predetermined light-dark pattern is applied to the image sensor, and measurement data is read out for each of the light sensors to determine whether the value is a predetermined value. However, a slight error is likely to occur in an optical system or the like that gives a predetermined pattern to the image sensor, and the accuracy of the brightness or light intensity distribution is not always higher than the accuracy of, for example, 8 bits of the measurement data. It is inevitable that the quality of each item varies to some extent, which is one of the factors that makes it difficult to determine the quality.

Another problem is that when the measurement data fluctuates, it cannot be determined whether the cause is the image sensor side or the data conversion circuit that converts the charge accumulation time into the measurement data. Of course, the operation of the data conversion circuit must be accurate, and if the measurement data fluctuates even slightly due to that, it must always be determined that it is defective, but the cause cannot be separated from the image sensor side In this case, an operation error that is not so large on the data conversion circuit side is overlooked.

Based on such circumstances, the present invention enables the operation of a data conversion circuit that converts the charge storage time in an image sensor circuit into measurement data to be tested independently of the image sensor side to determine the quality of the image sensor circuit. The purpose of the present invention is to clarify the test results for the entire circuit and determine the quality.

[Means for solving the problem]

In order to achieve the above object, the present invention provides an image sensor including a plurality of charge accumulation type photosensors for converting light intensity into charge accumulation time, and a time-lapse method for converting the charge accumulation time of each of the optical sensors into data. A measuring pulse generating circuit for generating a measuring pulse whose period changes in accordance with an operation command based on an operation command, a counting circuit for counting the measuring pulse and generating measuring data, A latch circuit that reads measurement data in accordance with a detection signal indicating a charge accumulation time from the sensor and stores the data for each optical sensor; and a detection signal from the optical sensor having the shortest charge accumulation time in the image sensor and a test signal provided in a test mode. And a starting circuit for outputting a logical sum of the test command and the operation command as the operation command.

[Action]

The measurement pulse generation circuit and the counting circuit in the above configuration constitute the above-mentioned data conversion circuit, and in the present invention,
Since the starting circuit which outputs the logical sum of the detection signal from the optical sensor with the shortest charge accumulation time in the image sensor and the test command given in the test mode as the operation command is provided,
In the test mode, a test command is given before the detection signal from the optical sensor with the shortest charge accumulation time is generated. (It is not always necessary to block the image sensor so that the detection signal from the optical sensor is not generated. No)
The operation of the measurement pulse generation circuit can be started without being affected by the fluctuation of the generation point of the detection signal from the optical sensor. Therefore, by reading the measurement data from the counting circuit that generates the measurement data by counting the measurement pulses generated by the measurement and examining the change with time, it is misleading by the clear pattern given to the image sensor and the error of the image sensor itself. The quality of the data conversion circuit can be determined without any problem.

In the image sensor circuit according to the present invention, a normal operation mode as the image sensor circuit can be selected in addition to the operation mode for the independent test for the data conversion circuit.

In the normal mode, in a state where a predetermined light and dark pattern is given to the image sensor, an operation command is given to the starting circuit according to a detection signal of the optical sensor having the shortest charge accumulation time in the image sensor as described in the above configuration. In this way, the measurement pulse generation circuit starts operation, generates a measurement pulse having the basic period most suitable for the light intensity distribution of the light and dark pattern received at that time, and uses this measurement pulse for each optical sensor to calculate the charge accumulation time. The measurement data converted from and stored in the latch circuit is read. Therefore, when the operation of the data conversion circuit is determined to be good in the above-described independent test mode, the quality of the operation of the image sensor can be more accurately determined from the measurement data read in the normal mode.

〔Example〕

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block circuit diagram of an embodiment of an image sensor circuit according to the present invention. FIG. 2 shows a specific circuit of an optical sensor and FIG. 3 shows waveforms related to the entire operation thereof.

The image sensor circuit 100 shown in FIG. 1 is for automatic focusing of the above-mentioned optical instrument, and usually uses a pair of image sensors 10, but only one is shown in the figure for simplicity. . Normally, several tens of optical sensors 11 are included in the image sensor 10. First, the content and operation of the optical sensor will be described with reference to FIG.

The two charge storage type optical sensors 11 shown in FIG. 2A are mainly composed of a photodiode 11a and a junction capacitor 11b thereof, and are connected in series with a starting transistor 11c to receive a power supply voltage V in a reverse bias direction. The same figure (b) for transistor 11c
When the reset pulse RP is applied and turned on, the junction capacitance 11
b is charged to the power supply voltage V, and the potential v at the interconnection point between the photodiode 11a and the transistor 11c is reset to 0 as shown in FIG. Thereafter, the junction capacitance 11b is discharged by the photocurrent generated according to the intensity of the light received by the photodiode 11a. Therefore, as shown in FIG. Get up on the slope.

The inverter 11d or the comparator shown in FIG. 7A receiving this potential v is used as a threshold element.
The detection signal DS of the optical sensor 11 shown in FIG.
Is set to "H" in this example simultaneously with the reset pulse RP, and falls to "L" when the potential v reaches its operation threshold value vt. The time T in the figure until the detection signal DS falls is the charge accumulation time of the optical sensor 11, and the light intensity is converted into the charge accumulation time.

In order to measure the length of the charge accumulation time T, a measurement pulse generation circuit 20 shown in the upper half of FIG. 1 is provided. The measurement pulse generation circuit 20 in this embodiment is composed of a basic clock generation circuit 21, a counter 22, a ROM 23, and a comparison circuit 24. The comparison circuit 24 among these generates a measurement pulse MP. The counting circuit 30 receiving the measurement pulse MP constitutes a data conversion circuit together with the measurement pulse generation circuit 30. The counting value obtained by counting the measurement pulse MP is placed on the bus 31 as measurement data D, and the address input A of the ROM 23 is input. And the latch circuit 40.

The operation of the image sensor circuit according to the present invention in the test mode is performed by the data conversion circuit including the measurement pulse generation circuit 30 and the counting circuit 40, which will be described below with reference to the waveform diagram of FIG.

In operating the image sensor circuit 100,
A reset pulse shown in FIG. 3A for resetting the operation of each optical sensor 11 of the image sensor 10 as described above.
RP is given first, and this is simultaneously
The basic clock generation circuit 21 and the counting circuit 30 of FIG. At this stage, the basic clock generation circuit 21 does not generate the basic clock BP yet, but starts counting the clock pulses CP immediately after the reset.

In order to put the operation of the circuit of the present invention into the test mode, a test command TS shown in FIG. 3 (b) is applied when a predetermined time has elapsed after the above-mentioned reset pulse RP. Give to circuit 60. The starting circuit 60 gives this to the basic clock generating circuit 21 as an operation command OS, and starts the operation of generating the basic clock BP shown in FIG. 3 (c).

The basic clock generation circuit 21 sees the time Te from receiving the reset pulse RP to receiving the operation command OS by counting the clock pulse CP as described above, and calculates this time Te based on the operation command OS. Two integer powers, for example 64
Immediately generates the basic clock BP having the cycle divided by.
The counter 22 has been cleared by an operation command OS received via an attached OR gate 22a, starts counting operation of this basic clock BP, and gives a count value to a comparison circuit 24. The comparison circuit 24 compares the count value of the counter 22 with the designated value received from the ROM 23, and each time the values match, the measurement pulse MP
Is generated and given to the counting circuit 30, and the OR gate 22
The count value of the counter 22 is cleared via a. The counting circuit 30 receiving the measurement pulse MP puts the count value on the bus 31 as the measurement data D. ROM23 is the measurement data D in this example.
Of the address input AD except for the lower 3 bits
A function for changing the period of the measurement pulse MP over time is stored in the form of a numerical table corresponding to the designated address.

Most simply, the values in this numerical table are 0 to 0 in the measurement data D.
7 is 8, 8 to 15 is 16 and so on, and the measurement data D is increased by 8 every time the measurement data D advances by 8. The numerical values in this table are the specified values as described above. ROM2
The data output DT of 3 is applied to the comparison circuit 24. The comparison circuit 24 compares the designated value from the ROM 23 with the data shown in FIG.
The counter 22 repeats the counting of the basic clock BP, and a measurement pulse MP whose period is gradually increased in this example is generated as shown in FIG.
In addition, the rate of increase of the measurement data D, which is the result of counting the measurement pulse MP by the counting circuit 30, gradually decreases as shown in FIG.

In the test mode, the measurement data D is read as described above, and it is checked whether or not the measurement data D changes with time correctly according to the numerical table set in the ROM 23.
In this embodiment, measurement data D
Only the least significant bit D0 that changes as shown in FIG. 3 (f) is read out via the buffer circuit 32.

It should be noted that the numerical table set in the ROM 23 is a function form most suitable for the application of the actual image sensor circuit, and is changed more finely and more complexly than the above.

Next, the operation in the normal mode will be described. Since this operation involves the latch circuit 40, this will be described first. The latch circuit 40 comprises the same number of latches 41 as the number of the optical sensors 11 in the image sensor 10. These latches 41 are connected to the bus 31, respectively, and the detection signals of FIG. In response to the DS, in this example, an operation of reading the measurement data D placed on the bus 31 is performed in synchronization with the fall from “H” to “L”.

The image sensor 10 is provided with a logic circuit section 12 attached thereto, and receives a detection signal DS from all of the optical sensors 11, and when any of the detection signals DS changes from “H” to “L”, the output thereof is output. To “H”. As can be easily understood, such an operation can be made by a NAND gate to which all the detection signals DS are input, and the output thereof is the shortest signal SE indicating the shortest charge accumulation time.

The starting circuit 50 supplies the shortest signal SE to the basic clock circuit 21 as an operation command OS, and causes the measurement pulse generating circuit 20 to start operation. As described above, the basic clock circuit 21 watches the time Te from receiving the reset pulse RP until receiving the operation command OS, and issues the basic clock BP at a period according to this time Te, that is, the shortest charge accumulation time. The operation of the measurement pulse generation circuit 20 and the counting circuit 30 after the start of the operation is the same as described above, and the measurement data D on the bus 31 is read into the latch 41 of the latch circuit 40 for each optical sensor according to the detection signal DS. Is memorized.

The logic circuit unit 12 incorporates, for example, a NOR gate that receives the detection signals DS from all the optical sensors 11 in the image sensor 10 in addition to the above, and all the detection signals DS have changed from “H” to “L”. The longest signal SL, which sometimes indicates the longest charge accumulation time, will now be issued. This longest signal
SL is applied to the basic clock circuit 21 to stop the operation of generating the basic clock BP and hence the measurement operation of the image sensor circuit 100, and is output to the outside as the end signal ED.

In order to read the measurement data stored in the latch circuit 40 based on the end signal ED, for example, a read command RS is repeatedly given to the address designating circuit 42 in the form of a pulse. Each time the addressing circuit 42 receives the read command RS, the address for the latch 41 in the latch circuit 40 is incremented, and the stored measurement data in each latch 41 is sequentially put on the bus 43 and output to the outside. To simplify external connections, a bus
Connect the 43 to the shift register and then output the measurement data serially.

The normal mode described above is, of course, an operation mode when the image sensor circuit 100 is used normally.After confirming the operation of the data conversion circuit in the test mode, the normal mode is switched to the normal mode, and the image sensor 10 is switched to the test mode. By reading the measurement data with the pattern given,
The quality of the image sensor can be accurately determined.

It should be noted that the circuit of the embodiment described above and the operation thereof are merely examples, and the present invention can be implemented in an appropriately modified form within the gist of the present invention.

〔The invention's effect〕

According to the present invention as described above, the starting of outputting the logical sum of the detection signal from the optical sensor having the shortest charge accumulation time in the image sensor and the test command given in the test mode to the measurement pulse generation circuit as an operation command A circuit is provided, and in the test mode, the measurement pulse generation circuit starts operating without being affected by the fluctuation of the generation point of the detection signal from the optical sensor in the image sensor, and the measurement pulse generated thereby is counted. Measurement data can be read from the counting circuit that generates the measurement data, and the changes over time can be examined.This eliminates the risk of errors in the test pattern given to the image sensor and errors in the image sensor itself as in the past. The accuracy of the operation of the data conversion circuit including the measurement pulse generation circuit and the counting circuit is accurately measured independently of other circuit parts. It is possible.

Further, according to the present invention, the operation is switched to the normal mode after the pass / fail of the data conversion circuit is determined, so that the measurement pulse having the basic starting time most suitable for the light intensity distribution of the test pattern received by the image sensor can be obtained. The quality of the operation of the image sensor can be accurately determined from the measured data obtained.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of an embodiment of an image sensor circuit according to the present invention, FIG. 2 is a specific circuit diagram of an optical sensor in the image sensor and a waveform diagram showing its operation, FIG. The figure is a waveform diagram illustrating the operation of the image sensor circuit of FIG. In the figure, 10: Image sensor, 11: Optical sensor, 11a: Photodiode, 11b: Photodiode junction capacitance, 11c: Transistor, 11d: Inverter, 12: Logic circuit section, 20: Measurement pulse generation circuit, 21: Basic Clock generation circuit, 22: counter, 23: R
OM, 24: comparison circuit, 30: counting circuit, 31: measurement data bus, 32: buffer circuit, 40: latch circuit, 41: latch, 42:
Addressing circuit, 43: Output bus for measurement data, 50: Start circuit, 100: Image sensor circuit, BP: Basic clock, CP:
Clock pulse, D: measurement data, D0: least significant bit of measurement data, DS: detection signal, ED: end signal, MP: measurement pulse, OS: operation command, RP: reset pulse, RS: read command, S
E: shortest signal, SL: longest signal, T: charge accumulation time, Te: shortest charge accumulation time, TS: test command, V: power supply voltage, v: potential in the optical sensor, vt: inverter operation threshold, It is.

Claims (1)

(57) [Claims] An image sensor including a plurality of charge accumulation type photosensors for converting light intensity into a charge accumulation time, and a measurement pulse whose period changes with time to convert the charge accumulation time of each of the photosensors into data. A measurement pulse generation circuit that starts the operation of generating the measurement pulse based on the operation command, a counting circuit that counts the measurement pulse to generate measurement data, and a charge accumulation time from each of the optical sensors. A latch circuit that reads the measurement data in accordance with the detected detection signal and stores the data for each optical sensor, and a logic between a detection signal from the optical sensor having the shortest charge accumulation time in the image sensor and a test command given in a test mode. A starting circuit that outputs the sum as the operation command.