JP2010045603A - Analog-digital mixed imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an analog-digital mixed imaging apparatus reducing fixed pattern noise to be periodically superimposed on a weak signal of an image sensor. <P>SOLUTION: The analog-digital mixed imaging apparatus is provided with: a delay generation circuit 110 which generates random delay time to each of reference horizontal synchronizing signals; a sensor drive circuit 105 which delays each of the reference horizontal signals based on the delay time generated to the reference horizontal synchronizing signals, and drives an image pickup device 100 by the delayed reference horizontal synchronizing signals; an AD converter 101; a memory 102 which stores output of the AD converter 101; and a memory drive circuit 106 which delays each of the reference horizontal synchronizing signals in the opposite directions, based on the delay time generated to the reference horizontal synchronizing signals, and drives the memory 102 by the reference horizontal synchronization signals delayed in the opposite directions. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an analog / digital mixed image pickup apparatus that digitizes image sensor output and the like, and in particular, mitigates periodic noise and countdown noise in subsequent stages due to noise generated when digitizing image sensor output and the like. It is about.

  In an imaging apparatus, an LSI in which an AFE unit (analog front end) for digitizing CCD sensor output and a digital signal processing unit for processing the digitized signal has been developed.

  The digital signal processing unit often performs periodic operations to generate various timings and drive the SDRAM memory. These operations leak as noise from the power supply of the LSI into the AFE unit, causing weak image sensors. There was a problem of being superimposed as noise on a simple analog signal.

As a solution to this problem, the timing generator of the digital signal processing unit is converted into a Gray code counter as in the analog / digital mixed IC described in Japanese Patent Laid-Open No. 4-196818 (Patent Document 1). There has been a method of reducing the influence on the analog signal by equalizing the load due to the simultaneous change of the generator.
Japanese Patent Laid-Open No. 4-196818

  However, even when a gray code counter is formed as in Patent Document 1, for example, a circuit that drives periodically and discretely, such as driving of an SDRAM memory, that is, a portion that cannot be gray-coded, solves noise superposition. There was a problem that I could not.

  Hereinafter, the configuration of a conventional analog / digital mixed imaging apparatus and an example of noise caused by driving an SDRAM memory will be described with reference to FIGS. FIG. 3 is a block diagram showing the configuration of a conventional analog / digital mixed imaging apparatus, and FIG. 4 is a diagram showing each signal of the conventional analog / digital mixed imaging apparatus.

  In FIG. 3, an analog / digital mixed image pickup apparatus includes an image pickup device 100, an AD converter 101, an SDRAM 103, a digital signal processing circuit 104, a sensor drive circuit 105, an SDRAM drive circuit 107, a reference horizontal sync pulse generation circuit 108, and a DA converter. 109.

  The image sensor 100 sequentially reads the first to nth lines of the sensor and the video signal in accordance with the line reading start pulse from the sensor driving circuit 105. The output sensor readout signal is converted into a digital signal by the AD converter 101, and signal processing is performed by the signal processing circuit 104. At the same time, the SDRAM 103 stores video signals necessary for various signal processing in accordance with the SDRAM drive pulse of the SDRAM drive circuit 107.

  In general, driving of an SDRAM or the like is burst transfer, and is performed periodically and discretely. Due to this periodic and discrete operation, noise is applied to a power supply or the like.

  Conventionally, since both the sensor driving circuit 105 and the SDRAM driving circuit 107 are driven by the reference horizontal synchronization signal from the reference horizontal synchronization pulse generating circuit 108, a weak sensor read signal from the image sensor 100 is used as a power source by driving the SDRAM. When noise is superimposed, as shown in FIG. 4, noise is superimposed on the first line read signal to the nth line read signal at the same timing position in each line, and as a result, the output image image of FIG. As shown in FIG. 3, the pattern appears as a periodic and discrete fixed pattern noise in the vertical direction with respect to the original image.

  Therefore, even when the gray code counter disclosed in Patent Document 1 is used, in a circuit that generates pulses periodically and discretely, a method such as gray coding cannot be used, and noise is applied to the power source or the like every time a pulse is generated. Therefore, periodic fixed pattern noise is superimposed on the weak signal of the image sensor.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an analog / digital mixed imaging apparatus capable of reducing fixed pattern noise periodically superimposed on a weak signal of an image sensor.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  That is, the outline of a typical one is based on a delay generation circuit that generates a random delay time for each of the reference horizontal synchronization signals used when driving the image sensor, and a delay time generated for the reference horizontal synchronization signal. Each of the reference horizontal synchronization signals is delayed, and the sensor drive circuit that drives the image sensor by the delayed reference horizontal synchronization signal, the analog-digital converter that digitizes the output of the image sensor, and the output of the analog-digital converter And a memory for driving the memory by the reference horizontal synchronization signal delayed in the reverse direction based on the delay time generated with respect to the reference horizontal synchronization signal. And a drive circuit.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  In other words, the effect obtained by a typical one is that noise superimposed on the weak analog signal of the image sensor is randomly generated by randomly varying the time difference between the noise generation source and the image sensor drive start timing. Noise is not noticeable.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

  The configuration and operation of an analog / digital mixed imaging apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing a configuration of an analog / digital mixed imaging apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing signals of the analog / digital mixed imaging apparatus according to an embodiment of the present invention. is there.

  In FIG. 1, an analog / digital mixed imaging apparatus includes an image sensor 100 as an image sensor, an AD converter 101, a FIFO memory 102, an SDRAM 103, a digital signal processing circuit 104, a sensor driving circuit 105, a memory driving circuit 106, and an SDRAM driving circuit. 107, a reference horizontal sync pulse generation circuit 108, a DA converter 109, a delay generation circuit 110 that generates a variable random delay time, a delay addition circuit 111, and a delay subtraction circuit 112.

  3 is the same operation as that of the conventional analog / digital mixed image pickup apparatus, and a duplicate description thereof will be omitted.

  The delay generation circuit 110 generates variable random delay times ΔT1 to ΔTn for each reference horizontal synchronization signal. The delay addition circuit 111 adds ΔT1 to ΔTn to the reference horizontal synchronizing signal and then supplies it to the sensor driving circuit 105. Similarly, the delay subtracting circuit 112 subtracts ΔT1 to ΔTn from the reference horizontal synchronizing signal and supplies the subtracted signal to the memory driving circuit 106.

  As a result, as shown in FIG. 2, the sensor driving circuit 105 generates a sensor first line readout start pulse to a sensor nth line readout start pulse in which ΔT1 to ΔTn are added to the reference horizontal synchronization signal by the delay addition circuit 111. Are supplied to the image sensor 100, and the image sensor 100 sequentially reads the first to n-th line readout signals.

  Further, by this operation, the sensor driving circuit 105 is in a state of being driven by changing the driving timing of the image sensor 100 at random.

  At this time, the periodic and discrete power supply noise generated by driving the SDRAM 103 or the like is superimposed on the sensor readout signal, but as shown in FIG. 2, the sensor first line readout signal to the sensor nth line readout signal are Since the time is shifted by ΔT1 to ΔTn, the relative time when noise is superimposed is different from the start of reading of the sensor.

  The FIFO memory 102 stores the AD-converted digital video signal in the memory, and sequentially reads out the memory first line to n-th line read signals in response to a memory read start pulse supplied from the memory driving circuit 106.

  Here, as shown in FIG. 2, the sensor line readout start pulse and the memory readout start pulse have a relationship of plus ΔT and minus ΔT, so that the video signal start position in the FIFO memory 102 has the same timing in the horizontal direction. I understand that.

  Further, by this operation, the memory drive circuit 106 is in a state of being read and driven by changing the memory read timing at random in synchronization with the sensor drive circuit 105.

  Then, the signal processing circuit 104 performs various kinds of signal processing, and as shown in the output image image of FIG. 2, conventionally, periodic and discrete fixed noise is superimposed as shown in FIG. In the present embodiment, it is superimposed as random noise, and the noise component can be made inconspicuous.

  In this embodiment, the operation for one screen has been described for the sake of explanation, but in reality, by generating a random ΔT between a plurality of screens, noise between the plurality of screens is further averaged and made conspicuous. Can be eliminated.

  Further, the FIFO memory 102 may be configured by a circuit using a shift register.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  The present invention relates to an analog / digital mixed imaging device that digitizes image sensor output and the like, and when digitizing image sensor output and the like, it is necessary to reduce periodic noise, countdown noise, and the like at the subsequent stage. And widely applicable to systems.

1 is a configuration diagram illustrating a configuration of an analog / digital mixed imaging apparatus according to an embodiment of the present invention. It is a figure which shows each signal of the analog / digital mixed imaging device which concerns on one embodiment of this invention. It is a block diagram which shows the structure of the conventional analog / digital mixed imaging device. It is a figure which shows each signal of the conventional analog / digital mixed imaging device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Image pick-up element, 101 ... AD converter, 102 ... FIFO memory, 103 ... SDRAM, 104 ... Digital signal processing circuit, 105 ... Sensor drive circuit, 106 ... Memory drive circuit, 107 ... SDRAM drive circuit, 108 ... Reference horizontal synchronization Pulse generation circuit 109... DA converter 110 110 delay generation circuit 111 delay addition circuit 112 delay subtraction circuit

Claims (3)

An analog / digital mixed imaging device that digitizes the output of an image sensor,
A delay generation circuit for generating a random delay time for each of the reference horizontal synchronization signals used when driving the image sensor;
Based on the delay time generated by the delay generation circuit, a sensor drive circuit that drives the image sensor by changing the drive timing at random, and
An analog-to-digital converter for digitizing the output of the image sensor;
A memory for storing the output of the analog-digital converter;
A memory driving circuit that reads and drives the memory read timing in a random manner in synchronization with the sensor driving circuit based on the delay time generated by the delay generating circuit; Digital mixed imaging device. An analog / digital mixed imaging device that digitizes the output of an image sensor,
A delay generation circuit for generating a random delay time for each of the reference horizontal synchronization signals used when driving the image sensor;
A sensor driving circuit for delaying each of the reference horizontal synchronization signals based on the delay time generated by the delay generation circuit, and driving the image sensor by the delayed reference horizontal synchronization signals;
An analog-to-digital converter for digitizing the output of the image sensor;
A memory for storing the output of the analog-digital converter;
A memory driving circuit for delaying each of the reference horizontal synchronization signals in the reverse direction based on the delay time generated in the delay generation circuit, and for reading and driving the memory by the reference horizontal synchronization signal delayed in the reverse direction; An analog / digital mixed imaging apparatus characterized by comprising: The analog / digital mixed imaging apparatus according to claim 1 or 2,
The analog / digital mixed imaging apparatus, wherein the reference horizontal synchronizing signal is used as a driving signal of an SDRAM driving circuit that drives an SDRAM used when processing a signal read from the memory.

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