JP2006135726A - Image signal processor and image signal processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image signal processor capable of performing black level correction and system offset correction in a short period of time. <P>SOLUTION: An input shutoff equivalent circuit 101 shuts off an input signal from a sensor, and outputs a signal having a level almost equivalent to an optical black level signal during system offset correction. A system offset correction circuit 107 conducts feedback control for a signal inputted into an addition circuit 103 via a D/A converter 108 so that a predetermined reference value is outputted from an A/D converter 105. Then, if the optical black level signal is outputted from the sensor, a digital OB correction circuit 106 determines a digital difference data in relation to the value outputted from the A/D converter 105 so as to output a predetermined black level value. An image signal subsequently outputted from the sensor is corrected so that deviation of black level may be offset. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is applied to, for example, a DSP (digital signal processing processor) of a camera for a mobile phone, and an image signal processing apparatus called an analog front end having an optical black level correction function and a system offset correction function. The present invention relates to an image signal processing method.

  A conventional image signal processing apparatus called an analog front end for CDD uses an external integration capacitance element (capacitor) for correcting a black level in a screen. (For example, refer to Patent Document 1). That is, during an optical black level output (hereinafter referred to as “OB”) period from a sensor (CCD or the like), the charge due to the difference (error) signal is integrated into a capacitor, and the accumulated charge is accumulated during the image signal output period. Is fed back to the input to cancel the system offset and the optical black level offset. As the capacitor, for example, a capacitor of about 0.1 μF is used for stabilizing the black level of the screen.

Further, as shown in FIG. 2, a black level correction is performed in an analog manner by a CDS (Correlated Double Sampling) circuit unit 501, an adder circuit 502, an analog OB correction circuit 503, a capacitor 504, and a gain variable amplifier 505, and an adder circuit. In some cases, offset correction is further performed using the A / D converter 507, the digital OB correction circuit 508, and the D / A converter 509.
JP 2004-80168 A

  However, in the above-described conventional image signal processing apparatus, it takes time until charges are accumulated in a capacitor having a relatively large capacity and an appropriate voltage is generated. Had a problem that the start-up time of the system becomes longer.

  In particular, in recent years, for example, mounting of a camera module on a mobile phone has become common, but the power of the mobile phone is usually the power source of the camera signal processing LSI mounted in the camera module and the built-in analog front end. Even if it is turned on, it is turned on when it is actually used instead of being put into a standby state, so that it is desired that black level correction can be performed in a shorter time, for example, within about 1 second.

  An object of the present invention is to make it possible to perform black level correction and system offset correction in a short time, and to shorten the startup time of the apparatus.

In order to solve the above problems, the present invention provides:
An image signal processing apparatus that receives a sensor output signal from an optical sensor and outputs a digital image signal,
A sampling circuit such as an interphase double sampling circuit for sampling the sensor output signal;
A gain variable amplification circuit for amplifying the output signal of the sampling circuit;
An analog / digital converter that converts the output signal of the variable gain amplifier circuit into a digital signal and outputs a converted digital signal; and
An input signal control circuit that shuts off the sensor output signal and inputs a predetermined reference voltage to the sampling circuit when correcting the characteristics of the image signal processing device;
An offset correction circuit that performs feedback control on a signal input to the variable gain amplifier circuit based on the converted digital signal at the time of the characteristic correction, and corrects an offset in the converted digital signal;
It is provided with.

  Further, a black level correction circuit is provided that outputs a predetermined black level value based on the converted digital signal when a predetermined optical black level signal is input from the optical sensor to the sampling circuit. It is characterized by that.

  As a result, the sensor output signal is interrupted, and feedback control is performed on the signal input to the variable gain amplifier circuit in a state where a predetermined reference voltage is input to the sampling circuit, and the offset in the converted digital signal is corrected. The The output value is corrected so that a predetermined black level value is output when a predetermined optical black level signal is input from the optical sensor.

  According to the present invention, black level correction and system offset correction can be performed in a short time, and the startup time of the apparatus can be shortened.

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

  An image signal processing device according to an embodiment of the present invention is, for example, an analog front end that forms part of an internal core of an LSI and connects between an image sensor such as a CCD sensor or a MOS sensor and a digital signal processing device. It is used as As shown in FIG. 1, the image signal processing apparatus includes an input cutoff / equivalent circuit 101, an interphase double sample circuit (CDS) 102, an adder circuit 103, a gain variable amplifier (PGA) 104, an A / D converter (ADC). 105, a digital OB correction circuit 106, a system offset correction circuit 107, and a D / A converter (DAC) 108.

  The input cutoff / equivalent circuit 101 includes, for example, a transfer gate, and outputs a signal input from the sensor as it is or outputs a predetermined reference voltage according to an input cutoff signal from the system offset correction circuit 107. It has become.

  The interphase double sample circuit 102 is configured to remove low-frequency noise included in the input signal (differential input signal) from the sensor.

  The adder circuit 103 adds the output of the interphase double sample circuit 102 and the output of the D / A converter 108.

  The variable gain amplifier 104 amplifies the signal from the adder circuit 103 to an optimum input range to the A / D converter 105 with a gain in a variable range of about 0 to 24 dB, for example, according to a control signal (not shown). It has become.

  The A / D converter 105 converts an analog signal output from the variable gain amplifier 104 into a digital code.

  The digital OB correction circuit 106 corrects the output value from the A / D converter 105 so that a predetermined black level value is output when an optical black level signal is input from the sensor.

  The system offset correction circuit 107 outputs an input cutoff signal to the input cutoff / equivalent circuit 101 and outputs a predetermined reference voltage regardless of the input signal from the sensor. Is output via the D / A converter 108 so that the signal is output.

  In the image signal processing apparatus configured as described above, the following operation is performed.

  First, the system offset correction circuit 107 outputs an input cutoff signal to the input cutoff / equivalent circuit 101 at a predetermined timing such as when the image signal processing device is initialized or when the gain of the variable gain amplifier 104 is changed. Therefore, the input cut-off / equivalent circuit 101 cuts off the input signal from the sensor and outputs a signal of a predetermined level, preferably a signal of a level substantially equivalent to the optical black level signal.

  The interphase double sample circuit 102, the adder circuit 103, the variable gain amplifier 104, and the A / D converter 105 operate in the same manner as when a normal image signal is input (the gain of the variable gain amplifier 104 is kept constant). The system offset correction circuit 107 feedback-controls the signal input to the adder circuit 103 via the D / A converter 108 so that a predetermined reference value is output from the A / D converter 105 at that time. To do. As a result, the A / D converter 105 outputs the signal having a level substantially equivalent to the optical black level signal input to the interphase double sampling circuit 102 as described above, due to the offset or the like of the variable gain amplifier 104 itself. A deviation (system offset) from a predetermined value generated in the digital code to be performed is corrected. At this time, the value output from the system offset correction circuit 107 is retained even after the feedback control is completed, and the offset is fixedly corrected. Here, since the control is performed in a state where the input signal from the sensor is cut off as described above, offset correction can be performed even if it is not an OB period in which the sensor outputs an optical black level signal.

  After that, when an optical black level signal is output from the sensor, the digital OB correction circuit 106 digitally outputs the value output from the A / D converter 105 so as to output a predetermined black level value at that time. Difference data is obtained, and thereafter, while the image signal is output from the sensor, correction (fine adjustment) is performed so as to cancel the deviation of the black level.

  Here, the recent technological evolution of CCD and MOS sensors is remarkable, and the generation of dark current when the screen is darkened is reduced. In particular, in the case of a MOS sensor, the voltage is as low as several mV. In an image signal processing apparatus (AFE system), the offset of the sampling circuit or PGA, that is, the system offset is more than the difference of the optical black level of the sensor. It is becoming dominant. Therefore, as described above, the system offset is first corrected, and then digitally accurate and fast optical black level correction is performed. An image signal processing apparatus that does not require a capacitive (external) integrating capacitive element can be configured. Therefore, the start-up time of the image signal processing device can be significantly shortened as compared with the case where the integration capacitor element is charged.

  When the input to the gain variable amplifier 104 is corrected based on the output from the A / D converter 105 as described above, the system offset correction needs to be performed every time the gain is changed. After setting the gain of the variable amplifier 104, system offset correction may be performed during the vertical blanking regression period of the screen, and then high-speed optical black level correction may be performed digitally during the OB period.

  The image signal processing apparatus and the image signal processing method according to the present invention can perform black level correction and system offset correction in a short time, and have an effect of shortening the start-up time of the apparatus. It is applied to a digital signal processor (DSP) for cameras, and is useful as an image signal processing apparatus and an image signal processing method called an analog front end having optical black level correction and system offset correction functions. It is.

It is a block diagram which shows the structure of the image signal processing apparatus of embodiment of this invention. It is a block diagram which shows the structure of the conventional image signal processing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Input interruption | blocking equivalent circuit 102 Interphase double sample circuit 103 Adder circuit 104 Gain variable amplifier 105 A / D converter 106 Digital OB correction circuit 107 System offset correction circuit 108 D / A converter

Claims (5)

An image signal processing apparatus that receives a sensor output signal from an optical sensor and outputs a digital image signal,
A sampling circuit for sampling the sensor output signal;
A gain variable amplification circuit for amplifying the output signal of the sampling circuit;
An analog / digital converter that converts the output signal of the variable gain amplifier circuit into a digital signal and outputs a converted digital signal; and
An input signal control circuit that shuts off the sensor output signal and inputs a predetermined reference voltage to the sampling circuit when correcting the characteristics of the image signal processing device;
An offset correction circuit that performs feedback control on a signal input to the variable gain amplifier circuit based on the converted digital signal at the time of the characteristic correction, and corrects an offset in the converted digital signal;
An image signal processing apparatus comprising: The image signal processing apparatus according to claim 1,
An image signal processing apparatus, wherein the sampling circuit is an interphase double sampling circuit. The image signal processing apparatus according to claim 1,
And a black level correction circuit for outputting a predetermined black level value based on the converted digital signal when a predetermined optical black level signal is input from the optical sensor to the sampling circuit. A characteristic image signal processing apparatus. A sampling circuit for sampling the sensor output signal from the optical sensor;
A gain variable amplification circuit for amplifying the output signal of the sampling circuit;
An analog / digital converter that converts the output signal of the variable gain amplifier circuit into a digital signal and outputs a converted digital signal; and
An offset correction circuit that performs feedback control on a signal input to the variable gain amplifier circuit based on the converted digital signal;
An image signal processing method using an image signal processing apparatus that receives the sensor output signal and outputs a digital image signal,
An image signal processing method comprising: cutting off the sensor output signal, inputting a predetermined reference voltage to the sampling circuit, and correcting an offset in the converted digital signal by the offset correction circuit. The image signal processing method according to claim 4,
Further, when a predetermined optical black level signal is input from the optical sensor to the sampling circuit, a value output from the image signal processing device becomes a predetermined black level value based on the converted digital signal. An image signal processing method characterized by correcting an output value as described above.

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