JPH0685675A - A/d converter - Google Patents

Abstract

PURPOSE:To apply A/D conversion with high resolution to only a required part. CONSTITUTION:Resistor strings R1-R192 which show n-bit resolution and resistor strings R193-R447 which show (n+a)-bit resolution are arranged in series in an A/D converter. The resistance value of the resistor string which shows (n+a)- bit resolution is set 1/2 times as much as that of the resistor string which shows the n-bit resolution, and digital output shows (n+a)-bits. Therefore, cost reduction, the reduction of a chip area, and low power consumption can be attained comparing with the case where the whole of A/D converter is made to high resolution.

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 and is mainly used for A / D conversion of nonlinear characteristics.

[0002]

2. Description of the Related Art FIG. 5 shows the configuration of a conventional 8-bit A / D converter. In this circuit, Rr1 to Rr256 having the same resistance value for generating the reference voltage are arranged in series,
Comparators Cc1 to Cc255 for comparing the respective reference voltage values with the analog input voltage Vin are arranged.
The outputs of these comparators are input to the encoder 11, and the 8-bit digital data 12 is output. Since the conventional 8-bit A / D converter has uniform resolution, there was no problem with the linear characteristic.
On the other hand, so that the analog output of the CCD is A / D converted,
When dealing with the non-linear characteristic, since the resistance values of the resistance strings that generate the reference voltages are equal, the resistance values are quantized at regular intervals, so that a part with sufficient resolution and a part with insufficient resolution occur, and The analog output A / D conversion could not be performed with sufficient resolution.

Heretofore, there has been a method of increasing the resolution of the A / D converter when dealing with nonlinear characteristics. For example, there is a case where an A / D converter having a resolution of 8 bits is replaced with an A / D converter having a resolution of 10 bits. When an A / D converter with 8-bit resolution is replaced with an A / D converter with 10-bit resolution, 8-bit A / D
In the case of a D converter, 255 comparators are required, but in the case of a 10-bit A / D converter, 1023 comparators are required.
Bits are disadvantageous in terms of power consumption and chip area, or have a large circuit scale or a complicated circuit configuration.

In the case of handling the non-linear characteristic, there has been a method of setting the value of each voltage dividing resistor to a different resistance value according to the non-linear characteristic. In this case, 8-bit A /
The D converter requires 255 comparators, and it is necessary to arrange resistors having different resistance values in series according to the non-linear characteristic, which again complicates the circuit configuration.

[0005]

As described above, according to the prior art, when A / D converting the non-linear characteristic, the circuit scale becomes large and the circuit configuration becomes complicated, resulting in an increase in power consumption and a chip. Problems such as increase in area occurred.

The present invention is to solve the above problems with a relatively simple structure.

[0007]

According to a method of increasing the resolution of an analog signal voltage by dividing a resistance series having a lower resistance value into only a portion requiring high resolution for an input analog signal.

That is, in the A / D converter of the present invention, a plurality of resistors are connected in series, and a predetermined voltage is applied to both ends of the resistors to generate a plurality of reference voltages from the connection points of the resistors. A column, a plurality of comparators for comparing the respective reference voltages with the input analog voltage and outputting the comparison result, and an encoder for outputting a digital signal of a predetermined number of bits based on the outputs from the comparators. A / with da
In the D converter, a first resistor string in which a plurality of resistors having a first resistance value are connected in series and a first resistor string having a relationship of 1/2 ^a (a: natural number) with respect to the first resistance value. Based on the output from the comparator and the resistor string in which a second resistor string in which a plurality of resistors having a resistance value of 2 are connected in series and the output from the comparator are input, When it is in the reference voltage range generated by the resistor string, an n-bit digital signal is output, and when the input analog voltage is in the reference voltage range generated by the second resistor string, (n +
a) The above encoder for outputting a bit digital signal is provided.

[0009]

It is possible to set high resolution only to the required portion of the A / D converter.

[0010]

EXAMPLE An example of the present invention for A / D converting the output of the CCD will be described below. As shown in FIG.
The relationship between the amount of light input to the CD and the output voltage is linear,
Since a CRT or the like that outputs CCD information has a gamma characteristic, it is not linear because it is corrected by the inverse gamma characteristic as shown in FIG. Here, if A / D conversion is performed between A and C with 8-bit resolution, the resolution between B and C becomes low. In order to obtain a resolution similar to that between A and B, a resolution higher than 8 bits is required between B and C.

For example, when quantization is performed with 8 bits between A and B, which is a low light amount region, and with 10 bits between a high light amount region B and C, A and B are divided into 191 steps and B is divided.
-C is divided into 254 steps, and the resolution is 8 bits as a whole (256 steps), but since there are 2 bits of auxiliary bits, 2 bits of auxiliary bits are added to the digital output after A / D conversion, It becomes a 10-bit digital output.

FIG. 4 shows the relationship between the digital output of the present invention and the analog input voltage, and FIG. 1 shows an embodiment of the circuit configuration of the present invention. In this circuit, a reference voltage Vref is provided between A and C in order to compare the analog input signal value Vin, the A side is set to GND, and the resistor strings R1 to R having 8-bit resolution are provided.
192, 10-bit resolution resistor series R193 to R4
47 are arranged in series, and there are comparators C1 to C446 for comparing Vref with each reference voltage value determined by each resistance voltage division, and the outputs of these comparators are provided to the encoder 1. The data is input and 8-bit output 2 and auxiliary 2-bit output 3 data is output. In the present invention, the resistance value may be selected according to the distribution of resolution, and when the resistance value from R2 to R192 is r, the resistance string R19
The resistance value of 3 to R447 may be set to a value of r / 4,
As a result, the resolution between B and C is increased by 2 bits as compared with that between A and B. As a result, the required resolution can be ensured even in a place where the analog input signal, which requires precision, is high. As a result, a resolution equivalent to 10 bits can be obtained with about 450 comparators.

Furthermore, since the present invention has an 8-bit basic bit, the quantized value can be handled in the same manner as a conventional A / D converter, so that it can be applied to not only nonlinear characteristics but also linear characteristics. It is possible.

The present invention is not limited to the above embodiment.

[0015]

As described in detail above, according to the present invention,
It is possible to realize an A / D converter that can set high resolution only in a necessary part without setting the entire A / D converter to high resolution,
As a result, cost reduction, chip area reduction, and power consumption reduction are possible due to the efficient device configuration.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an A / D converter according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the amount of incident light and the output voltage of a CCD.

FIG. 3 is a diagram showing a relationship between a CCD output and a camera output, and an inverse gamma-characteristic and a camera output.

FIG. 4 is a diagram showing a relationship between a quantized value of a digital signal and an analog input voltage.

FIG. 5 is a circuit configuration diagram of a conventional A / D converter.

[Explanation of symbols]

 1 Encoder 2 8-bit digital output signal line 3 Auxiliary 2-bit digital output signal line R1 to R447 Voltage dividing resistors for setting reference voltage C1 to R446 Comparator Vin Analog voltage value Vref Reference voltage

Claims (1)

[Claims] 1. A resistor string in which a plurality of resistors are connected in series and a predetermined voltage is applied to both ends thereof to generate a plurality of reference voltages from a connection point of the resistors, the reference voltages, and an input analog. In an A / D converter having a plurality of comparators that compare a voltage and output a comparison result, and an encoder that outputs a digital signal of a predetermined number of bits based on the output from the comparators, A first resistance string in which a plurality of resistances having a first resistance value are connected in series and a second resistance value having a relationship of 1/2 ^a (a: natural number) with respect to the first resistance value A second resistor string in which a plurality of resistors are connected in series is connected in series, and an input analog voltage is generated from the first resistor string based on the output from the comparator. N-bit digit when within the reference voltage range And an encoder for outputting a digital signal of (n + a) bits when the input analog voltage is within the reference voltage range generated by the second resistor string. A / D converter.