JPH06276098A - A/d converter - Google Patents

Abstract

PURPOSE:To easily vary conversion characteristics by providing the number of voltage divider resistors more than resolution and optionally selecting a voltage division output to be connected to a comparator. CONSTITUTION:This A/D converter is equipped with 10-bit voltage-division output terminals for the digital output of an 8-bit encoder 4 and voltage division output terminals to be connected to comparators C1-C255 which compare measured voltages inputted from an input terminal 6 with a reference voltage are selected by selection switches S1-S255 of a wiring pattern formed in a single wiring layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flash type A / D converter for converting an analog input signal into a digital signal.

[0002]

2. Description of the Related Art A conventional flash type A / D converter is shown in FIG.
As shown in, the ladder resistors R1 to i (i = 2 ⁿ ) are connected in series between the upper reference voltage terminal 35 and the lower reference voltage terminal 36, and the voltage dividing output terminal between the resistors is connected to the comparator 32.
Connect to. In the comparator 32, the measured voltage input from the analog input terminal 37 is compared with the divided voltage output input from each divided voltage output terminal. The output of the comparator 32 is input to the encoder 33 and is output from the output terminal 34 as an n-bit digital signal.

If the resistance ratio of the ladder resistance is set to have a predetermined non-linear characteristic in the above structure, then FIGS.
As shown in FIG. 5, non-linear A / D conversion can be performed without including the analog amplifier 11 having a non-linear voltage characteristic or the digital circuit 22 for performing a linear conversion operation in the preceding stage or the subsequent stage of the A / D converter 12. . For example, γ correction of an image pickup apparatus used for video signal processing is performed by A / D shown in FIG.
For the ladder resistors R1 to Ri of the converter,

[0004]

[Equation 1]

It can be realized by giving the characteristics of.

[0006]

However, in the above-mentioned conventional flash type A / D converter, the voltage dividing output terminal connected to each comparator is uniquely determined regardless of linear type or non-linear type. The comparator was comparing the measured voltage with a fixed voltage divided output. Therefore, A
Since the conversion range of the A / D converter cannot be arbitrarily set, the conversion accuracy cannot be easily corrected, and even when A / D conversion is necessary only in a part of the voltage range,
There was a problem that conversion had to be performed within the voltage range of the entire system.

Further, in the linear A / D converter, A / D conversion must be performed over the entire voltage range with the same accuracy as that of the portion requiring the highest resolution, which increases the cost of the entire system. There was a problem to invite. Further, when a special conversion process is required such as the above-mentioned nonlinear A / D conversion, a general-purpose A / D converter cannot be used, which complicates the design and significantly increases the cost. There was a problem inviting.

An object of the present invention is to provide in advance a number of voltage dividing resistors whose resolution is equal to or higher than the resolution of a digital output signal so that the voltage dividing output connected to a comparator can be easily changed. The conversion range and conversion accuracy of the converter can be changed arbitrarily, and it can be applied to use with a special conversion characteristic, the conversion accuracy can be easily corrected, and the yield in the production stage can be improved. It is to provide an A / D converter capable of performing the above.

[0009]

The A / D converter of the present invention comprises a plurality of voltage dividing resistors connected in series between reference voltages and a plurality of voltage dividing resistors for comparing an analog input voltage with a voltage dividing output of each voltage dividing resistor. An A / D converter for converting an analog input voltage into a digital output signal, which has a number of voltage dividing resistors equal to or higher than the resolution of the digital output signal, and is connected to each of the plurality of comparators. It is characterized in that a partial pressure selecting means for selecting a partial pressure output is provided.

The voltage division selecting means may be a wiring layer which is arranged exchangeably between the plurality of voltage dividing resistors and the plurality of comparators.

Further, the voltage dividing selection means is based on the resistance value storage means for rewritably storing the voltage division resistance value to be input to each of the plurality of comparators, and the contents stored in the resistance value storage means. It may be configured by a selector that selects a divided voltage output terminal connected to the comparator.

[0012]

In the present invention, the voltage division output connected to each of the comparators can be selected by the voltage division selection means. When the divided voltage output connected to the comparator is changed, the divided output value input to the comparator changes, and the conversion characteristic also changes.

Further, by forming the voltage division selecting means by a single wiring layer for connecting each of the comparators to a predetermined voltage division output, the conversion characteristic changes only by changing the configuration of the wiring pattern in the wiring layer.

Further, the voltage division selection means is connected to each comparator based on the resistance value storage means for rewritably storing the voltage division output to be connected to each of the comparators and the stored contents of the resistance value storage means. Selector to select the voltage division output terminal to
With this configuration, the conversion characteristics are changed by rewriting the stored contents of the resistance value storage means.

[0015]

1 is a diagram showing the configuration of an A / D converter according to an embodiment of the present invention. This embodiment is an embodiment of the nonlinear A / D converter according to the invention described in claim 2, and
Outputs a bit digital signal. A / D converter 1
Connects the ladder resistors R _{1 to} R ₁₀₂₅ in series between the reference voltage upper point 2 and the reference voltage lower point 3 and draws the divided voltage output terminals T _{1 to} T ₁₀₂₄ from between the resistors. The divided voltage output terminals T _{1 to} T ₁₀₂₄ have an analog input terminal 6 at one terminal.
It is selectively connected to the lower terminals of the comparators C _{1 to} C ₂₅₅ to which the measured voltage is input from. Comparator C ₁ ~
The output of C ₂₅₅ is input to the encoder 4. The encoder 4 outputs an 8-bit digital signal from the output terminal 5 according to the outputs of the comparators C _{1 to} C ₂₅₅ .

Selection switches S _{1 to} S are provided between the voltage dividing output terminals T ₁ to T ₁₀₂₄ and the comparators C _{1 to} C _255.
A resistance selection unit 7 consisting of ₂₅₅ is provided. The resistance selection unit 7 is formed by patterning the reference voltage selection switches S _{1 to} S ₂₅₅ on _one wiring layer. In this embodiment,
The final 8-bit output signal is provided with voltage-dividing output terminals T _{1 to} T ₁₀₂₄ for 10 bits, and each of the reference voltage selection switches S _{1 to} S ₂₅₅ constituting the resistance selection unit 7 is a comparator. the divided output terminal to be connected to each of the C ₁ -C ₂₅₅ fixedly selects.

When the A / D converter 1 configured as described above is provided with a characteristic suitable for γ correction in the video signal processing, each resistance value of the resistors R _{1 to} R ₁₀₂₅ is 1 ohm. Then, in the above formula 1, R _T is 1025.
Becomes Ω, and γ = 0.45, and each of the divided voltage output terminals T _{1 to} T
_When the combined resistance value R _i from the lower point 3 of the reference voltage of ₁₀₂₄ is calculated from the equation 1, R _i T = (i / 256) ^0.45 · 1025. Selecting a divided voltage output terminal to be connected to the respective comparators C ₁ -C ₂₅₅ using this. That is, when i = 1, R ₁ T = (1/256) ^{0 · 45} · 1025 = 84, and the comparator C ₁ is connected to the voltage dividing output terminal T ₈₄ . Similarly, when i = 2 and i = 255, R _2T
= 115 and R _255T = 1023, and the comparator C
₂ and C ₂₅₅ are connected to the divided voltage output terminals T ₁₁₅ and T ₁₀₂₃ , respectively.

Actually, when the wiring layer 7 is formed by photolithography, a wiring pattern for connecting the divided voltage output terminals to be connected, which are obtained as described above, to the respective comparators C _{1 to} C ₂₅₅ is formed. .

As described above, the voltage dividing output terminals corresponding to the desired non-linear characteristics are selectively selected by the comparators C ₁ to C.
By connecting to each of the _255, a non-linear A / D converted digital signal of the measured voltage is output from the output terminal 5. As described above, the reference voltage selection switches S ₁ to
Since S ₂₅₅ is created by photolithography as a wiring pattern in a single wiring layer, an A / D converter having different nonlinear conversion characteristics can be easily obtained only by changing a single mask pattern in this photolithography. Can be created.

The number of resistors connected in series between the reference voltage upper point 2 and the reference voltage lower point 3 may be larger than the number of bits of the output signal of the encoder 4, and is limited to 10 bits in this embodiment. is not.

FIG. 2 shows A according to the invention described in claim 3.
It is a figure which shows the structure of a / D converter.

In the A / D converter 11, the reference voltage terminal 12 is grounded via the ladder resistors R _{0 to} R _n connected in series, the voltage _dividing output terminals T _{0 to} T _n are provided between the resistors, and the encoder 1 is used.
4 is provided with comparators C _{0 to} C _m (m <n) according to the number of bits of the digital output signal. The measured voltage is input from the analog input terminal 16 to one input terminal of each of the comparators C _{0 to} C _{m, and} the voltage _dividing output terminals T _{0 to} T _n are selectively connected to the other input terminal. Selectors S _{0 to} S _m are provided for the comparators C _{0 to} C _m , respectively.

Each of the selectors S _{0 to} S _m includes
Of the voltage division output terminals T _{0 to} T _n, a plurality of voltage division output terminals that can be connected to the comparator to which the selector corresponds are connected, and a single voltage division output is output from the plurality of voltage division output terminals. Select the pin and connect it to the comparator.
Further, selection data is supplied from the memory 19 to each of the selectors S _{0 to} S _m . Each of the selectors S ₀ to S _m is the decoder is provided, the selector S ₀ to S
Each of _m selects the voltage division output terminal to be connected to the comparators C _{0 to} C _m according to the contents of this selection data.
The memory 18 is a rewritable nonvolatile memory such as an EEPROM, and stores selection data supplied to each of the selectors S _{0 to} S _m .

In the above structure, the A / D converter 11 can be integrally formed in a single LSI. In this case, the ladder resistors R _{0 to} R _n are metal resistors, diffusion resistors,
It can be formed using a known structure such as a polysilicon resistor or a transistor resistor. If the number of divisions is increased in a part of the ladder resistance, it is possible to partially perform A / D conversion with high resolution. Also, the reference voltage terminal 1
2 can be connected to the power supply of the LSI.

With the above configuration, the voltage division output terminals connected to the comparators C _{0 to} C _m are selected according to the selection data stored in the memory 18, and are compared with the measured voltage in each of the comparators C _{0 to} C _m. The partial pressure output value is determined. Therefore, by rewriting the stored contents of the memory 18, it is possible to change the divided voltage output value to be compared with the measured voltage in each of the comparators C _{0 to} C _m , and to change the resolution after manufacture or to correct the conversion characteristic. It can be done easily.

Further, the total number m of the comparators C is set to an 8-bit precision (m = 255), and the total number n of the ladder resistors R is 1.
By using 0-bit resistance division (n = 1023), an A / D converter partially having 10-bit resolution can be obtained. With this configuration, A
Since the A / D conversion LSI has a high chip occupancy rate of the comparator and the chip size and power consumption are substantially determined by the total number of comparators, the chip cost is higher than that of the conventional A / D conversion LSI having the same resolution. And the power consumption can be reduced to about 1/4.

The above structure can be implemented not only in the flash type A / D converter but also in the successive approximation type and other A / D converters having a reference voltage generating circuit.

[0028]

According to the present invention, the voltage value to be compared with the analog input voltage in the comparator can be selected from a plurality of voltage-divided outputs according to the desired conversion characteristic, and the voltage-dividing resistor and the comparator can be selected. There is an advantage that any conversion characteristics can be dealt with without changing the configuration of.

Further, an A / D converter suitable for arbitrary conversion characteristics can be obtained by forming the voltage dividing selection means for determining the connection state between the voltage dividing output terminal and the comparator in a single wiring layer. Can be easily created.

Further, the voltage division output terminals to be connected to the respective comparators are stored in the rewritable resistance value storage means, and the voltage division output terminals connected to the respective comparators are stored based on the stored contents of the resistance value storage means. By providing the selector for selecting, there is an advantage that the conversion characteristic can be easily changed even after the A / D converter is manufactured by rewriting the stored contents of the resistance value storage means.

[Brief description of drawings]

1 is an A / D that is an embodiment of the invention described in claim 1;
It is a figure which shows the structure of a converter.

FIG. 2 is an A / D that is an embodiment of the invention described in claim 2;
It is a figure which shows the structure of a converter.

FIG. 3 is a diagram showing a configuration of a conventional A / D converter.

FIG. 4 shows a nonlinear A / D conversion using a conventional linear A / D converter.
It is a figure which shows the structure at the time of performing D conversion.

[Explanation of symbols]

 1, 11-A / D converter 2, 12-reference voltage 3,13-reference voltage 4,14-encoder 5,15-output terminal 6,16-input terminal 7-wiring layer 18-memory R-resistance T- Voltage division output terminal C-Comparator S-Selector

Claims (3)

[Claims] 1. A digital input device for analog input voltage, comprising: a plurality of voltage dividing resistors connected in series between reference voltages; and a plurality of comparators for comparing an analog input voltage with a voltage dividing output between the voltage dividing resistors. An A / D converter for converting into a signal and outputting the signal is provided with a voltage dividing resistor having a number equal to or higher than the resolution of the digital output signal, and a voltage dividing selecting means for selecting a voltage dividing output connected to each of the plurality of comparators. A / D characterized by being provided
converter. 2. The A / D converter according to claim 1, wherein the voltage dividing selection means is a wiring layer which is arranged so as to be exchangeable between the plurality of voltage dividing resistors and the plurality of comparators. 3. The resistance division memory means rewritably stores the division resistance value to be inputted to each of the plurality of comparators, and each of the resistance division memory means based on the contents stored in the resistance value storage means. The A / D converter according to claim 1, further comprising a selector that selects a divided voltage output terminal connected to the comparator.