JPS5912619A - Automatic correcting method of analog-digital converter - Google Patents

Abstract

PURPOSE:To simplify the measurement of correction amount, by using a comparator and a sample holding circuit provided to an A/D converter for attaining the measurement of correction amount. CONSTITUTION:A voltage synthesizing a low-order and a high-order DAC output when a digital input code of a high-order DAC is set suitably and a low-order DAC is set to full-scale, is Vs, where Da is a set digital code. The other code Db corresponding to the Vs is obtained by sampling and holding the voltage Vs and A/D-converting the result with a local DAC having a characteristic of A. Then, a Dc(=Db-Da) is obtained to all codes of the high-order DAC. Then, an optional analog input voltage Vd is A/D-converted with the characteristic A. A digital code Dg as same as the result of D/A conversion in an ideal characteristic I is obtained by subtracting the Dc from the result of conversion in this case. Thus, the simplicity of the measurement of the correction amount is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic correction method for an analog-to-digital converter, and more particularly, to a method for measuring a correction amount on a single sheet of paper, which can be easily automated.

In an analog-to-digital converter, the amount of deviation of the digital output value from the expected value is called an error.This error includes quantization error, linearity error, offset error, etc.; Since the accuracy of a digital converter is determined by the magnitude of the error, it is necessary to correct the error.

Conventionally, in order to obtain the correction amount of an analog-to-digital converter (hereinafter referred to as an N-width converter), the output of a local digital-to-analog converter (hereinafter referred to as a local DAC), which is normally connected only to a comparator, is somehow The output voltage for the local DAC input code was determined by measuring the output voltage with a high-precision voltmeter. However, this has the following drawbacks.

(1) A high-precision voltmeter is required, and currently this type of equipment is expensive and takes a long time to measure θ, so it takes a lot of time to find the correction amount for one chip, reducing productivity. do.

(2) Errors caused by the comparator cannot be corrected.

(3) It is necessary to output the local DAC output externally.

In the case of (3), if the output resistance of the local DAC is low,
Although the local DAC output can be directly output to the outside, the wiring for external output is long, and pads, pins, etc. are added, and measurement accuracy is degraded due to noise induced there. When the output resistance of the local DAC is high, or to reduce the noise mentioned above, it is possible to connect a buffer amplifier to the local DAC output and output the buffer amplifier output to the outside, but in this case, the error of the buffer amplifier It is included in the measured value and degrades measurement accuracy.

In order to eliminate these drawbacks, the present invention uses a comparator and a sample-and-hold circuit included in the A/L converter instead of a measuring device such as a voltmeter. This is intended to simplify the measurement of the correction amount and improve productivity, and the drawings will be described in detail below.

FIG. 1 is a diagram explaining the principle of the present invention. Here, the digital-to-analog converter that generates the output of the upper digit is connected to the upper DA.
The digital-to-analog converter that generates the output of the lower digit of C1 will be referred to as a lower DAC. Local DAC-C' is a combination of the upper DAC and lower DAC. In FIG. 1, A represents the characteristics of the entire DAC, and L represents the characteristics of the lower DAC and 1M represents the characteristics of the upper DAC. L is lower I
) is the full scale of A C, and p is the I of the lower DAC.
It is LSB. Upper and lower D when the digital input code of the upper DAC is set appropriately and the lower DAC is set to full scale (setting digital code is Da)
The total output voltage obtained by combining the AC outputs is .

(1) By sampling and holding the voltage V in a sample-and-hold circuit and converting it from analog to digital using a local DAC having characteristics of A, the other code Db corresponding to V5 can be obtained. Therefore, Db Da
"" Dc .

Take this. o = 1). Let's call it K. Next, an arbitrary analog input voltage Vd is converted from analog to digital using the characteristics of the local DAC. The ceremony that takes place at this time.

Find it from Df. By subtracting
You can get a digital code of 8.

+21 Instead of sampling and holding V5,
Sample and hold V5+1, which is larger than I LSB, and generate the corresponding digital code D. In search of D
A similar correction amount can also be obtained by calculating the correction amount from the equation: e-(Da+1)=Do---...+3+.

Measuring the amount of correction using this method does not require a measuring device such as a voltmeter, and has the advantage that the amount of correction can be automatically measured using a simple control and addition circuit assembled with a digital circuit.

Figure 2 (1) and (2) are the local areas of the present invention]) A C
(1) is an example in which ■5 is sampled and held, and (2) is an example in which ■, +1 is sampled and held.

The circuit in (1) is a general 7-ray capacitor I) A C
This is an example in which DACs are used as upper and lower DACs. (2
) circuit sets the capacitance of the IC, which should always be grounded, to Vre.
It is characterized in that it can be switched between f and ground using the control terminal Cb.

(1), (both the 210 circuits have switch Sa on the ground side,
S.

When the switch 5e-1 is connected to the Vref side, the full scale of the lower DAC is output, and in the circuit (2), when the switch Sb is further connected to the Vref side, an output larger than the full scale of the lower DAC by ILSB is obtained. At this time, if the digital inputs from B(1) to B(f-hn=1) are appropriately set and switch S5 is closed, the voltage of ■5 or v5+1 shown in FIG. 1 is sampled, and switch S5 When opened, it is held. In this way,
Analog-to-digital conversion is performed using a method such as successive approximation using a comparator so that the output OUT becomes the ground level, and a digital code Db is obtained.

As explained above, according to the correction method of the present invention, it is possible to use a conventional local DAC as is, and the correction amount can be calculated using a simple digital circuit without using a measuring device such as a high-precision voltmeter. Since the measurement can be performed automatically, there is no need to increase the circuit scale, which has the advantage of improving productivity and reducing costs.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the principle of the present invention, and FIG. 2 is a diagram showing an embodiment of a local digital-to-analog converter according to the present invention. 5o=JL+m~1...Ground, Vref selector switch, 8a...Ground, A person selector switch, S,...
・Discharge switch, 1c to 21n 5
2...Capacity, BO-J+m-1...Digital input, sb...Ground, Vref selector switch, ca,
Cb, I) S80.2 Switch control signal terminal

Claims (1)

[Claims] (1) The first digital signal that generates the output of the upper digits
an analog converter; a local digital-to-analog converter configured to add the output of the first digital-to-analog converter and the output of the second digital-to-analog converter to obtain an analog output. In the automatic correction method for an analog-to-digital converter having a converter, the first digital-to-analog converter's digital input code is set, and the output of the second digital-to-analog converter is set to full-scale output or full-scale output. ILS from scale
Make it thicker by B, sample and hold the output voltage at this time, find a digital input code that outputs a voltage equal to this voltage by analog-to-digital conversion, find the difference between this code and the preset code, and do the same thing. (For all digital input codes of the first digital-to-analog converter) [Find this difference, and calculate the amount of correction for the input code of any first digital-to-analog converter by the amount of correction for the input code smaller than that input code. An automatic correction method for an analog-to-digital converter, characterized by performing summation.