JP2008209735A - Focus detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a color temperature sensor from being affected by correction operation for removing fixed pattern noise before accumulation of an AF sensor. <P>SOLUTION: In a focus detecting device arranging a first sensor 113 for outputting a signal for detecting a focus by phase difference detection and a second sensor 110 having a plurality of pixels mutually different in spectral sensitivity on the same substrate, the accumulation of the second sensor 110 is started after correction operation for removing the fixed pattern noise of the first sensor 113. The accumulation start timing of the second sensor 110 is obtained by delaying the correction operation start timing of the first sensor 113 with a counter. Alternatively, the accumulation start timing of the second sensor 110 is synchronized with the correction operation completion of the first sensor 113. The influence of power source voltage fluctuation due to the correction operation of the first sensor 113 can be reduced, and the second sensor 110 can perform stable accumulation operation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a focus detection apparatus for autofocus used for a single-lens reflex camera or the like.

  As a focus detection device for autofocus, there is a passive method in which luminance information of a target is received by an optical sensor and a focus position is detected by electrical processing. Among them, the phase difference detection method is a method of detecting a lateral shift of the luminance signal in the two sets of light receiving elements.

  In autofocus (hereinafter referred to as AF) of a phase difference detection method used in a single-lens reflex camera, there is a problem that a focus detection position varies depending on a color temperature of a subject light source. This is due to chromatic aberration of the lens. An example of a focus detection apparatus that solves this problem is disclosed in Patent Document 1.

  This apparatus has a focus detection AF sensor and a color temperature sensor, and has a correction means for correcting the output of the AF sensor based on the output of the color temperature sensor. The photosensor array of the AF sensor and the pair of photodiodes of the color temperature sensor are disposed adjacent to each other in the AF sensor module.

On the other hand, as disclosed in Patent Document 2, there is a focus detection device in which AF sensor accumulation control is performed by detecting the difference between the maximum value and the minimum value of the sensor output in order to increase the AF speed. This has an offset cancel mode in which the fixed pattern of each output amplifier that detects the maximum value and the minimum value is removed and a correction operation is performed before the AF signal accumulation operation in order to perform more accurate control.
JP-A 63-168613 JP 2000-180706 A

  However, the apparatus of Patent Document 1 does not show the influence of the AF correction operation on the color temperature sensor.

  In recent AF sensors, the number of pixels is increasing as the number of ranging points increases. As a result, when the AF sensor correction operation (offset cancellation operation) as shown in Patent Document 2 is performed, the power supply voltage fluctuation of the integrated circuit is increased, and the influence of the power supply voltage fluctuation on other circuit operations is ignored. I can't. The color temperature sensor mounted on the same substrate as the AF sensor is no exception, and the accumulation level of the color temperature sensor is shaken by the power supply voltage fluctuation due to the correction operation of the AF sensor. It has occurred.

  On the other hand, as a method for reducing fluctuations in power supply voltage, a method of well-isolating a noise source circuit is generally used. However, it is not easy to suppress the shaking of the color temperature sensor by well separation. This is because the pixel of the color temperature sensor and the pixel of the AF sensor are arranged close to each other so that the color temperature sensor region on the finder covers the distance measuring region of the AF sensor. That is, there may be a case where there is not enough space for well separation between the pixels of the color temperature sensor and the AF sensor. In addition, since the number of pins of the sensor package cannot be easily increased due to a request for camera miniaturization, it is difficult to provide a pin for another power source.

  Therefore, an object of the present invention is to obtain an accurate color temperature sensor output without being influenced by an offset cancel operation for an AF sensor when performing a highly accurate AF operation using the color temperature sensor output. It is. As a result, it is an object of the present invention to provide a focus detection device capable of realizing a highly accurate AF operation.

  In order to solve the above problems, a focus detection apparatus according to the present invention includes a first sensor that outputs a focus detection signal by phase difference detection and a second sensor having a plurality of pixels having different spectral sensitivities on the same substrate. In the focus detection apparatus disposed above, accumulation of the second sensor is started after completion of the correction operation for removing the fixed pattern noise of the first sensor.

  In the present invention, accumulation of the color temperature sensor as the second sensor is started after completion of the correction operation for removing the fixed pattern noise of the AF sensor as the first sensor. As a result, the influence of the power supply voltage fluctuation due to the correction operation of the AF sensor can be reduced, so that the color temperature sensor can perform a stable accumulation operation. As a result, it is possible to discriminate subject light sources having different color temperatures, and it is possible to detect the focus with high accuracy by correcting the focus adjustment information based on the discrimination information.

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

  In any of the embodiments, the color temperature sensor in the focus detection apparatus is used for correcting chromatic aberration of the AF sensor, as in the prior art. The AF sensor and the color temperature sensor are arranged on the same substrate.

[Embodiment 1]
FIG. 1 is a circuit block diagram showing Embodiment 1 of the present invention.

  101 is a serial communication clock input terminal, 102 is a serial communication enable signal input terminal, and 103 is a serial communication data input terminal. 104 is a serial communication I / O circuit, 105 is a counter circuit that delays and outputs an input signal for a certain period, 106 is an oscillation circuit that generates a master clock of a logic circuit, and 107 is a timing generation circuit (hereinafter referred to as TG) for a color temperature sensor 108 are AF sensor TGs. These constitute a logic block 109.

  Reference numeral 110 denotes a color temperature sensor as a second sensor having a plurality of pixels having different spectral sensitivities described in FIG. 4, reference numeral 111 denotes a sample hold circuit, and reference numeral 112 denotes a gain circuit. Reference numeral 113 denotes an AF sensor as a first sensor described in FIG. 3 that outputs a focus detection signal by phase difference detection. 114 is an automatic gain control (AGC) circuit, and 115 is a gain circuit. 116 is an output multiplexer, 117 is an analog signal output terminal, 120 is a color temperature sensor forced accumulation end signal, 121 is an AF sensor correction operation start signal, 122 is an AF sensor forced accumulation end signal, and 123 is a main clock.

  124 is a color temperature sensor accumulation start signal, and 125 is a color temperature sensor accumulation completion signal. 126 is a drive signal for the color temperature sensor 110, the sample hold circuit 111, and the gain circuit 112, 127 is an AF sensor accumulation completion signal, and 128 is a drive signal for the AF sensor 113, the AGC circuit 114, and the gain circuit 115.

  130 is a color temperature sensor integration signal, 131 is a sample hold signal, 132 is a color temperature sensor output signal, 133 is an AF sensor maximum signal and minimum signal, 134 is an AF sensor maximum signal, minimum signal and bit signal, 135 is an AF sensor output Signal 136 is an analog output signal.

  Drive signals 126 and 128 represent a plurality of control signals. The drive signal 126 transmits the accumulation start timing and accumulation end timing of the color temperature sensor 110, the sample hold timing of the sample hold circuit 111, and the read timing of the gain circuit 112. The drive signal 128 transmits the correction operation of the AF sensor 113, the maximum / minimum output during accumulation, the completion of accumulation, the signal readout timing, the AGC timing of the AGC circuit 114, and the readout timing of the gain circuit 115.

  FIG. 3 is a circuit diagram of the AF sensor according to the first embodiment of the present invention.

  The circuit of the AF sensor which is the first sensor will be described with reference to FIG.

  Although only two pixels are shown in the figure, in practice, in order to detect a phase difference, one AF line is formed by several tens of pixel arrays and corresponds to one distance measuring point. In recent years, with the increase in the number of distance measuring points, the total number of pixel arrays has reached several thousand.

  301 is a photodiode reset voltage (VRES), 302 is a photodiode reset switch (SW_RESET), and 303 is a photodiode. Reference numeral 304 denotes a current source (IBIAS0), 305 denotes a storage control switch (SW_CHG), and 306 denotes a capacitor (C_CHG) that holds a storage signal.

  Reference numeral 307 denotes a noise recording switch 1 (SW_N1), and reference numeral 308 denotes a noise recording switch 2 (SW_N2). 309 is a signal output switch 1 (SW_S1), 310 is a signal output switch 2 (SW_S2), 311 is a capacitor (C_CLAMP) for holding fixed pattern noise of each pixel, 312 is a clamp switch (SW_CLAMP), 313 is a clamp voltage (VGR) ).

Reference numeral 314 denotes a current source (IBIAS1) of the source follower circuit, reference numeral 315 denotes a minimum signal output and pixel selection switch (SW_PH) which is turned on at the time of minimum signal output and bit output, and reference numeral 316 denotes a minimum signal output terminal. 317 is a current source (IBIAS2) of the source follower circuit, 318 is a maximum signal output terminal, and 319 is a maximum signal output switch (SW_PAGC). Each switch and current source in Fig. 3 is TG for AF sensor Connected to and driven by 108. The minimum signal output terminal 316 and the maximum signal output terminal 318 are connected to the AGC circuit 114 and the gain circuit 115.

  FIG. 4 is a circuit diagram of the color temperature sensor according to the first embodiment of the present invention.

  The circuit of the color temperature sensor as the second sensor will be described with reference to FIG.

  401 is a photodiode reset voltage (VRST), 402 and 403 are pixels having different spectra, for example, 402 is a photodiode (R pixel) in which a red color filter is formed, 403 is a photodiode (in which a red color filter is not formed) W pixel).

  404 is an integration circuit reset switch (SW1), 405 is a switch (SW2) that fixes one side of the integration capacitor to the reference voltage during the reset period to remove the offset of the integration amplifier, and 406 is an offset removal similar to the switch 405 Switch (SW3). Reference numeral 407 denotes an integration capacitor (C_INT) that determines the gain of the color temperature sensor, 408 an operational amplifier, 409 a storage end voltage (VCOMP), and 410 a comparator that compares the output of the operational amplifier 408 with the storage end voltage (VCOMP) 409.

  Each switch in FIG. 4 is connected to and driven by the color temperature sensor TG 107. The output of the comparator 410 is connected to the color temperature sensor TG 107 through the color temperature sensor accumulation completion signal 125. The outputs of the integration amplifiers of the R pixel and the W pixel are sampled and held by the sample hold circuit 111 through the color temperature sensor integration signal 130.

  FIG. 5 is a diagram illustrating the correction operation of the AF sensor and the color temperature sensor and the drive timing at the start of accumulation according to the first embodiment of the present invention.

  Symbols in the figure indicate the switches, current sources, capacitor storage voltages, and comparator input voltages.

  Hereinafter, an operation sequence of the AF sensor and the color temperature sensor will be described.

  A serial signal for starting the AF correction operation is input from the outside to each of the terminals 101, 102, and 103 in FIG. In response to this, the I / O circuit 104 outputs an AF correction operation start signal 121. The AF sensor TG 108 receives this signal and turns on the current sources (IBIAS1) 314 and (IBIAS2) 317. Current source (IBIAS0) 304 is always on. The current sources (IBIAS1) 314 and (IBIAS2) 317 are turned on, and the switches (SW_RESET) 302, (SW_N1) 307, and (SW_N2) 308 are turned off. At this time, a signal including the reset noise of the photodiode, the offset of the differential stage, and the kTC noise of each switch is written to the capacitor (C_CHG) 306. Since these noises have different noise values for each pixel, they appear as fixed pattern noise in the pixel array.

  When this fixed pattern noise information is written in the capacitor (C_CHG) 306, the current sources (IBIAS1) 314 and (IBIAS2) 317 are turned off. Next, the switches (SW_S1) 309, (SW_CLAMP) 312 and (SW_S2) 310 operate sequentially, and the noise written in the capacitor (C_CHG) 306 is subtracted to remove the fixed pattern noise of the pixel and the readout circuit. The signal output state is ready. This series of operations is called a correction operation. During the correction operation period, several thousand current sources (IBIAS1 314 and IBIAS2 317) in the integrated circuit perform on / off operations simultaneously.

  In the conventional driving method, the on / off operation fluctuates the power supply voltage of the integrated circuit, affecting other circuits on the integrated circuit. In addition to the correction operation, the signal source can be read as a period during which the current source is turned on / off. However, in the present invention, the current source that performs the on / off operation is limited to a line for reading a signal. Therefore, the power supply voltage fluctuation amount due to the on / off operation of the current source is smaller than that in the correction operation, and the influence on the color temperature sensor is small.

  After the switch (SW_S2) 310 is turned on, the switches (SW_PH) 315 and (SW_PAGC) 319 are turned on to short-circuit the outputs of the pixel array. By driving the shorted wiring with one current source, the maximum value and the minimum value of the pixel array are detected. The maximum value and the minimum value are input to the AGC circuit 114, and automatic gain control (AGC) is performed based on the difference between the maximum value and the minimum value. The AGC circuit 114 outputs an accumulation completion signal 127 to the AF sensor TG 108, and from there, outputs an accumulation end signal to the AF sensor 113, and the accumulation operation is completed. In addition, by performing serial communication from the outside, it is also possible to forcibly end the accumulation of the AF sensor and the color temperature sensor by outputting the color temperature sensor forced accumulation end signal 120 and the AF sensor forced accumulation end signal 122. . Although reading of the AF sensor is not shown in FIG. 3, SW_PH 315 of each pixel is sequentially turned on by the shift register, and a bit signal is output from the minimum signal output terminal 316 to the gain circuit 115. An appropriate gain is applied by the gain circuit 115.

  Next, the sequence of the color temperature sensor will be described. The AF correction operation start signal 121 is input to the color temperature sensor TG 107 after being delayed by the counter circuit 105. The counter circuit 105 has a delay amount that is the same as the AF correction operation or a period that is extended by the number of master clocks from the end of the correction operation. The color temperature sensor TG 107 receives the color temperature sensor accumulation start signal 124 delayed by the counter circuit 105 and sequentially drives the switches (SW1) 404, (SW2) 405, and (SW3) 406. When the output of the operational amplifier 408 changes from the reset voltage (VREST) 401 and reaches the storage end voltage (VCOMP) 409, the comparator 410 operates to transmit the storage completion to the color temperature sensor TG 107. An accumulation end signal is output from this, the switches (SW1) 404, (SW2) 405, and (SW3) 406 return to the reset state, and the sample hold circuit 111 holds the accumulation signal. A gain is applied to the held signal by the gain circuit 112.

  The color temperature sensor output signal 132 and the AF sensor output signal 135 to which the gain is applied are multiplexed by the output multiplexer 116 and output from the analog signal output terminal 117.

  In the conventional driving method, the correction operation start signal of the I / O circuit 104 is input to the color temperature sensor TG 107 without being delayed by the counter circuit 105. For this reason, the output voltage of the operational amplifier 408, that is, the input voltage of the comparator 410, varies due to the AF correction operation, particularly the on / off operation of the current sources (IBIAS1) 314 and (IBIAS2) 317. When the fluctuating signal exceeds the accumulation end voltage (VCOMP) 409, the comparator 410 erroneously recognizes that the accumulation has been completed and sends an accumulation completion signal to the logic block 109. As a result, the sample-and-hold circuit 111 has a problem that the changed signal is held and a signal different from the optical signal is output.

  In the present invention, accumulation of the color temperature sensor is started after completion of the AF correction operation. In this embodiment, the correction operation start signal of the I / O circuit 104 is delayed by the counter circuit 105, and after the AF correction operation is completed, the color temperature sensor reset is released and the accumulation of the color temperature sensor is started. . As a result, the influence of the power supply voltage fluctuation caused by the AF correction operation on the accumulation operation of the color temperature sensor can be reduced. As a result, a stable output corresponding to the photocurrent can be obtained from the color temperature sensor.

[Embodiment 2]
FIG. 2 is a circuit block diagram of the second embodiment of the present invention.

  The numbers in the figure are the same as in FIG.

  The difference from the first embodiment is that the accumulation start signal 124 of the color temperature sensor is output from the TG 108 for AF sensor. Of the signals input from the AF sensor TG 108 to the AF sensor 113, a signal (for example, SW_S2) that operates after the AF correction operation ends is used as the accumulation start signal of the color temperature sensor. That is, the color temperature sensor accumulation start timing is synchronized with the completion of the AF sensor correction operation at the point where the accumulation of the color temperature sensor is started after the AF correction operation is completed.

  By doing so, the same effect as in the first embodiment can be obtained without using a counter circuit.

[Embodiment 3]
FIG. 6 shows an integrated circuit used in the focus detection apparatus equipped with the AF sensor and color temperature sensor according to the first and second embodiments of the present invention.

  In FIG. 6, reference numeral 601 denotes a logic block similar to 109, which corresponds to a plurality of AF sensors and a plurality of color temperature sensors. Reference numeral 602 denotes an AF sensor L1A composed of several tens of pixel arrays, and reference numeral 603 denotes an AF sensor L1B. The AF sensor L1A 602 and the AF sensor L1A 602 correspond to one distance measuring point. 604 is an AF sensor L23A, 605 is an AF sensor L24B, 606 is an AF sensor block, 607 is a color temperature sensor, 608 is a sample hold circuit, 609 is a gain amplifier, 610 is a color temperature sensor unit, and 611 is a color temperature sensor block .

  612 is an AGC circuit 1, 613 is an AGC circuit 2, 614 is an AGC circuit 3, 615 is an AGC circuit 4, and the AGC circuit 4 transmits the maximum and minimum signals of 23 pairs of AF sensors to 612 to 615 in a time-sharing manner. Sequential accumulation control reduces the number of AGC circuits. 616 is a reference voltage current generation circuit, 617 is a thermometer circuit, 618 is an AF gain circuit, 619 is an output multiplexer, and 620 is an analog circuit block.

  621 is an integrated circuit used for the focus detection device, 622 is a serial communication terminal of 101 to 103, 623 is a reference voltage output terminal, 624 is an external thermometer diode connection terminal, and 625 is an analog signal output terminal.

  Although the connection information is not shown in the figure, the logic block 601 controls the circuits of the AF sensor block 606, the color temperature sensor block 611, and the analog circuit block 620 by external serial communication. The signal of the AF sensor block 606 is controlled to be accumulated by the AGC circuits 612 to 615, and the accumulation completion signal is transmitted to the logic block 601. The signal of the AF sensor block 606 is gain-applied by the AF gain circuit 618 and taken out from the analog signal output terminal 625 through the output multiplexer 619 including the signal of the color temperature sensor block 611. The reference voltage and reference current generated by the reference voltage / current generation circuit 616 are supplied to the blocks 601, 606, 611 and 620. Some signals can be extracted from the analog signal output terminal 625 through the serial communication terminal 622 or the output multiplexer 619.

[Embodiment 4]
FIG. 7 is a configuration diagram of a camera system showing Embodiment 4 of the present invention.

  This is a system in which the focus detection apparatus of the present invention is incorporated in a digital camera.

  Reference numeral 701 denotes a barrier that serves as a lens switch and a main switch, which will be described later. Reference numeral 702 denotes a lens that forms an optical image of a subject on a solid-state image sensor. Reference numeral 703 denotes a stop for adjusting the amount of light that has passed through the lens. Reference numeral 704 denotes a solid-state imaging device that captures a subject imaged by a lens as an image signal. Reference numeral 705 denotes a focus detection device that includes the AF sensor and the color temperature sensor described in the first or second embodiment or the integrated circuit of the third embodiment. is there.

  Reference numeral 706 denotes an imaging signal processing device that performs signal processing on signals output from the solid-state imaging device and the focus detection device, and 707 denotes an A / D converter that performs analog-to-digital conversion on the signals output from the imaging signal processing circuit. A signal processing unit 708 performs various corrections or data compression on the image data output from the A / D converter.

  709 is a memory unit for temporarily storing image data, 710 is an external I / F circuit for communicating with an external computer, and 711 is a timing generation unit that outputs various timing signals to the signal processing unit. 712 is an overall control / control operation unit for controlling various operations and the entire camera, 713 is a recording medium control I / F unit, 714 is a removable recording medium such as a semiconductor memory for recording or reading on the recording medium, Reference numeral 715 denotes an external computer.

  Next, the operation at the time of shooting of the digital camera will be described.

  When the barrier 701 is opened, the main power supply is turned on, then the control system power supply is turned on, and the power supply of the imaging system circuit such as the A / D converter 707 is turned on. Next, based on the signal output from the focus detection device 705, the overall control / calculation unit 712 calculates the distance to the subject by detecting the phase difference as described above. Thereafter, it is determined whether or not the lens 702 is driven and in focus. If it is determined that the lens 702 is not in focus, the lens 702 is driven again to perform autofocus control.

  Next, the main exposure starts after the in-focus state is confirmed. When the exposure is completed, the image signal output from the solid-state imaging device 704 is converted from analog to digital by the A / D converter 707, and is written into the memory unit 709 through the signal processing unit 708 and overall control / calculation. Thereafter, the data stored in the memory unit 709 is recorded on the removable recording medium 714 through the recording medium control I / F unit 713 under the control of the overall control / arithmetic unit 712. Further, it may be input directly to a computer or the like through the external I / F unit 710.

1 is a circuit block diagram showing a first embodiment of the present invention. Circuit block diagram showing Embodiment 2 of the present invention 1 is a circuit diagram of an AF sensor showing Embodiment 1 of the present invention. 1 is a circuit diagram of a color temperature sensor showing Embodiment 1 of the present invention. Drive timing chart showing Embodiment 1 of the present invention Configuration diagram of focus detection integrated circuit showing Embodiment 3 of the present invention Configuration diagram of a camera system showing Embodiment 4 of the present invention

Explanation of symbols

105 ... Counter circuit
106: Oscillator circuit
107 ... TG for temperature sensor
108 ... TG for AF sensor
110… Color temperature sensor (second sensor)
113… AF sensor (first sensor)
112,115 ... Gain circuit
121: AF correction operation start signal
124 ... Color temperature sensor accumulation start signal
303… Photodiode
306 ... Capacity to hold the accumulated signal
311… Capacity to hold fixed pattern noise
316 ... Minimum signal output terminal
318 ... Maximum signal output terminal
402 ... Photodiode (R pixel)
403 ... Photodiode (W pixel)
410 ... Comparator
411 ... Color temperature sensor
601… Logic block
611… Color temperature sensor block
620 ... Analog circuit block

Claims (5)

  In a focus detection apparatus in which a first sensor that outputs a focus detection signal by phase difference detection and a second sensor having a plurality of pixels having different spectral sensitivities are arranged on the same substrate, the first sensor is fixed. A focus detection apparatus, wherein accumulation of the second sensor is started after completion of a correction operation for removing pattern noise.   The focus detection apparatus according to claim 1, wherein the accumulation start timing of the second sensor is obtained by delaying the correction operation start timing of the first sensor by a counter.   The focus detection apparatus according to claim 1, wherein the accumulation start timing of the second sensor is synchronized with completion of the correction operation of the first sensor.   Through the correction operation period of the first sensor, the current source of the source follower circuit connected to the maximum signal output terminal or the minimum signal output terminal of the first sensor via a switch is turned on and off. The focus detection apparatus according to claim 1.   A camera system equipped with the focus detection apparatus according to claim 1.

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