JPH07226682A - A/d converter - Google Patents

Abstract

PURPOSE:To automatically adjust amplification gain to a proper waveform size for every input analog signal by generating a control signal for amplification gain based on a present digital signal output value and a stored digital signal value. CONSTITUTION:An amplified analog signal waveform is converted into a digital signal 6 in an A/D conversion part and the maximum value of the signal 6 in a comparison part 11 for a prescribed period is stored in a memory 12. Next, the maximum value of the memory 12 and the maximum reference value of a memory 13 are read and the values are compared in a comparison part 14. When the maximum value of the signal 6 is smaller than the maximum reference value, a standard reference value is read from the memory 13. When the maximum value of the signal 6 is smaller than the standard reference value, a signal 7 adjusting the gain of a variable amplifier is generated in a control signal generation part 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an A / D converter having a function of automatically adjusting the magnitude of an input analog signal to the dynamic range of an A / D converter.

[0002]

2. Description of the Related Art In the conventional A / D converter shown in FIG. 4, an analog signal 24 having an amplitude waveform larger than a specified input value of an A / D converter 22 is input to the A / D converter 22. In that case, the A / D converter 22 will be in an overflow state, and the accuracy of the signal processing system in the subsequent stage will be significantly reduced. Because, when the analog signal 24 in the excessive input state is input, the digital signal output 26 of the A / D converter 22
Is fixed to the maximum value that the A / D converter 22 can take in the overflow state. Therefore, for example, even when the analog signal 24 in the excessive input state is a Sin wave, the distorted wave is A / D converted. This is because, as a result, in the signal processing system in the subsequent stage, the frequency component that is not originally included in the input Sin wave signal is also targeted for signal processing.

On the other hand, even if an analog signal much larger than the maximum value of the analog signal 24 input to the A / D converter 22 in a normal state is input, a sufficient margin is ensured so that overflow does not occur. Although the deterioration of the signal processing accuracy due to the overflow is suppressed, the dynamic range of the A / D converter 22 cannot be effectively used because it causes an unnecessary margin in the normal state. This is also a disadvantage in improving the S / N ratio. Therefore, as shown in FIG.
The analog signal 24 (FIG. 5) is, for example, 256 gradations (8
In the case of FIG. 3A, which is equal to the dynamic range of the A / D converter 22 of (bit quantization), it is correctly quantized and converted into the digital signal output 26 as shown in FIG. Further, in FIG. 3C, the analog signal 24 is A / D.
When the dynamic range of the converter 22 is exceeded,
The digital value after A / D conversion of a signal waveform with 256 gradations or more is fixed at 256. Therefore, it is necessary to lower the gain of the variable amplifier 21 provided in the preceding stage of the A / D converter 22 so that the gain falls within the dynamic range as shown in the signal waveform of FIG. In addition, (d) in FIG.
If the size of the analog signal 24 is small, S /
Since it is not preferable in terms of N, in order to make full use of the dynamic range as shown in the signal waveform of FIG.
It is necessary to increase the gain of the variable amplifier 21.

For this purpose, the gain of the variable amplifier 21 is set to a desired value by manually adjusting the volume and the like, and the maximum value of the analog signal 25 input to the A / D converter 22 is appropriately set. The digital signal output 26 of the A / D converter 22 is 2 out of 256 gradations.
It was converted to 50. However, since there are various kinds of input analog signals 24, such as a video signal of a natural image and a video signal including characters, an appropriate waveform size is different for each input signal waveform. Therefore, it is necessary to adjust the gain of the variable amplifier 21 every time the input signal is changed, and the adjustment operation is frequently performed, which is a troublesome problem in use.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an A / D converter having a function of automatically adjusting the size of an appropriate waveform for each input analog signal. The purpose is to provide.

[0006]

In order to achieve the above object, the magnitude of an input analog signal waveform is adjusted by changing the gain of an amplifier, and the adjusted analog signal is quantized at a predetermined sample time and quantization. In an A / D conversion device for converting a digital signal at a level, a first comparison unit that compares a current digital signal output value with a stored maximum digital signal value, and a comparison result of the first comparison unit to obtain a current If the digital signal output value is larger, the maximum value memory that updates and stores the maximum digital signal value stored with the current digital signal output value, the memory that stores the reference signal value, and the predetermined period A second comparison unit that compares the maximum digital signal value in the reference signal value with the reference signal value, and a control signal generation unit that generates a gain control signal based on the comparison result of the second comparison unit. Consisting of a control unit for controlling the various sections.

[0007]

[Operation] With the above-mentioned configuration, the maximum value memory is
For example, the maximum digital signal value of one frame is stored. The second comparison unit compares the current digital signal output value and the digital signal value stored in the maximum value memory,
When the signal values are equal to each other, or when the maximum digital signal value is larger than the reference signal value, the control signal generation unit generates and outputs the control signal for reducing the gain of the amplifier, and the maximum digital signal. When the value is smaller than the reference signal value, the control signal generation unit generates and outputs the control signal for increasing the gain of the amplifier.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An A / D converter according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of one embodiment of an A / D converter according to the present invention. 11 is A
The first comparing unit compares the current value of the digital signal 6 output from the / D converter (not shown) with the stored maximum digital signal value 8. 12 is the first comparison unit 11
According to the comparison result of, for example, when the value of the current digital signal 6 is larger than the stored maximum digital signal value 8, the stored maximum digital signal value is the value of the current digital signal 6. It is a maximum value memory for updating and storing the value of 8. Reference numeral 13 is a memory that stores a reference signal value, for example, a maximum reference value, a standard reference value, a maximum digital signal value 8 and the like. 14 is within a predetermined period, for example, 1
It is a second comparison unit that compares the maximum digital signal value 8 of the frame period and the like with the reference signal value to determine the magnitude. 1
Reference numeral 5 is a control signal generation unit that generates a signal 7 for adjusting the gain of the variable amplifier (not shown) based on the comparison result of the second comparison unit 14. Reference numeral 16 is a control unit that controls each unit.

The operation of the A / D converter according to the present invention will be described with reference to the flow charts of FIGS. 1 and 3. In step 1, when the analog signal waveform of the video signal is input to the variable amplifier (not shown), the variable amplifier amplifies the analog signal waveform with a predetermined gain for a predetermined period, for example, one frame period. Then, the amplified analog signal waveform is converted into the digital signal 6 by the A / D converter. On the other hand, the maximum value of the digital signal 6 in the predetermined period is stored in the maximum value memory 12. In step 2,
The maximum value of the digital signal 6 is read from the maximum value memory 12. In step 3, the maximum reference value stored in the memory 13 is read out, and the digital signal 6 is read by the second comparing section 14.
Of the digital signal 6 is smaller than the maximum reference value (NO), the standard reference value stored in the memory 13 is read out in step 4, and the second comparison is performed. The maximum value of the digital signal 6 is compared with the standard reference value in the section 14, and if the maximum value of the digital signal 6 is smaller than the standard reference value (YES), in step 5, the control signal generating section 15 controls the variable amplifier. The signal 7 for adjusting the gain so as to increase the gain by one step is generated, and the process returns to step 3. When the maximum value of the digital signal 6 is larger than the maximum reference value in step 3 (YES), the gain of the variable amplifier is adjusted by the control signal generation unit 15 in step 6 so as to be decreased by one step, for example. Generate signal 7 and return to step 3. In step 3, when the maximum value of the digital signal 6 is larger than the standard reference value (NO),
finish. Therefore, when an 8-bit A / D converter is used, the maximum reference value in the above flowchart is set to, for example, 2
If 55 is set and the standard reference value is set to 250, the gain of the amplified analog signal waveform 5 is automatically adjusted so as to be within the range of 250 to 255 which is close to the upper limit of the dynamic range of the A / D converter. It Further, the reference signal value is stored in the plurality of memories 13, and the required reference signal value is selected. As an example, in the case of a video signal of a night view, it is not always preferable in terms of image quality to amplify the signal in the dynamic range. In that case, for example, the amplification of the analog signal waveform may be limited to a value of 1/2 of the dynamic range.

[0010]

As described above, the present invention provides an A / D conversion device provided with a function of automatically adjusting the size of a suitable waveform for each input analog signal. Therefore, for example, when handling various video signals such as a multimedia personal computer, there is no need to manually adjust the gain of the amplifier for each input video signal, and there is an advantage that a convenient and simple device can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an A / D conversion device according to the present invention.

FIG. 2 is a diagram showing the relationship between the size of an analog signal and the dynamic range of an A / D converter with 256 gradations (8-bit quantization).

FIG. 3 is a flowchart showing the operation of the A / D conversion device according to the present invention.

FIG. 4 is a block diagram of an embodiment of a conventional A / D conversion device.

[Explanation of Codes] 6 Digital Signal 7 Signal for Adjusting Gain 8 Maximum Digital Signal Value 11 First Comparison Section 12 Maximum Value Memory 13 Memory 14 Second Comparison Section 15 Control Signal Generation Section 16 Control Section 21 Variable Amplifier 22 A / D Converter 24 Analog signal waveform 25 Analog signal input to A / D converter 22 Digital signal output

Claims (5)

[Claims] 1. The size of an input analog signal waveform is
In the A / D conversion device that adjusts by changing the gain of the amplifier and converts the adjusted analog signal into a digital signal at a predetermined sample time and quantization level, the current digital signal output value and the maximum digital value stored A first comparison unit that compares the signal value, if the current digital signal output value is larger in the comparison result of the first comparison unit,
A maximum value memory that updates and stores the maximum digital signal value stored with the current digital signal output value, a memory that stores a reference signal value, a maximum digital signal value within a predetermined period, and the reference A second comparison unit that compares the signal value to determine the magnitude, a control signal generation unit that generates a gain control signal based on the comparison result of the second comparison unit, and a control unit that controls each unit. An A / D conversion device characterized by clearing the contents of a value memory every predetermined period. 2. The maximum digital signal value before one predetermined period is stored in the memory, and the maximum digital signal value is compared with a reference signal value to determine the magnitude. The A / D conversion device according to claim 1. 3. The second comparing section compares a maximum digital signal value with the reference signal value, and when the signal values are equal to each other, or the maximum digital signal value is larger than the reference signal value. In this case, the A / D conversion device according to claim 1, wherein the control signal generation unit generates and outputs a control signal for reducing the gain of the variable amplifier. 4. The second comparison unit compares a maximum digital signal value with the reference signal value, and when the maximum digital signal value is smaller than the reference signal value, the control signal generation unit is variable. The A / D converter according to claim 1, wherein a control signal for increasing the gain of the amplifier is generated and output. 5. The A / D converter according to claim 1, wherein a plurality of reference signal values are stored in the memory, and one of the reference signal values is selected and compared with the maximum digital signal value. .