JPS63299614A - Adjusting device for a/d converter - Google Patents

Abstract

PURPOSE:To adjust the MSB of a converter with a high accuracy without needing an accuracy for a measuring instrument by minimizing the input level of the conveter, preventing a high order bit excluding a maximum bit MSB from being operated and shifting the low order bit to operate, to the high order bit. CONSTITUTION:An oscillator 1 is inputted to an A/D converter 2, the bit of a high order bit '0' or below excluding the MSB of respective bit outputs of an output 0, here, a 12th bit to a 16th bit (LSB) are connected from the high order bit of, a D/A converter 4 up to a 6th bit, and the input up to the LSD less than a low order 7 bit is not executed, and on the other hand, while the D/A converting output is monitored by a distortion factor meter 5, a vari able resistor for fine adjustment of the current source of the MSB of the A/D converter is adjusted, and adjusted so that the distortion can be minimum. In this case, the output level of a D/A converter comes to be a large level only by the shifted part, the accuracy of the D/A converter rises for that part, and on the other hand, the S/N of a measuring system is improved. Only for the part to input the level small, the adjustment of the MSB is executed without needing the accurary of the oscillator and the distortion factor meter.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in an adjustment device for adjusting nonlinearity in an A/D converter.

(Conventional contact) A device that digitizes audio signals in an A/D converter requires high speed and high precision, and for this reason, D
A successive approximation type with a /A converter is used. Here, an analog signal such as an audio signal has both positive and negative polarities, and when the level is low, it is converted around the center of the input level of the A/D converter. Therefore, the maximum beep) (MS
If the accuracy of B) is poor, the distortion will be constant regardless of the input level, and the distortion will be exactly the same as the zero-cross distortion of a transistor amplifier. For this purpose, the internal D/A converter M
Adjust SB. At this time, conventionally, a sine wave with low distortion was input to the input of the A/D converter, the digital signal was Fourier transformed, and the harmonics were adjusted to the minimum, or D/A conversion was performed again to convert it into an analog signal with distortion. I measured it and corrected it to reduce the distortion.

(Problems to be Solved by the Invention) In the above, the former requires advanced measuring equipment such as a Fourier transformer, and complicated adjustment of the A/D converter is required. A highly accurate A converter is required, and the oscillator and distortion meter also need to be highly accurate, especially for those with 16 bits or more.
You will need something of higher quality than above.

In view of these circumstances, the present invention provides highly accurate A/D conversion and adjustment of the MSB of these measuring instruments without requiring high accuracy.

(Measures to solve the problem) Reduce the input level of the A/D converter so that several bits of the upper pits except for the MSB do not operate, remove only those pits that do not operate, and change the lower pits that do operate to the D/D converter. Shift to the upper pit of A conversion.

As a result, the output level of the D/A converter increases by the amount of the shift, and the accuracy of the j5 D/A converter increases by that amount, while the S/N of the measurement system improves. Furthermore, by inputting a smaller level, the MSB can be adjusted without requiring the accuracy of the oscillator and distortion meter. This will be explained below along with examples.

(Example) An example of the present invention will be described. FIG. 1 shows an example in 16 bits, and FIG. 2 shows an explanatory diagram of the same.

Input oscillator 1 to A/D converter 2, digital output 0
Upper pits excluding the MSB of the valley bit output Pits below O1, here from the 12th bit to the 16th Bit (L
SB) is connected from the upper pit to the 6th bit of the D/A converter 4, and inputs below the lower 7 pits up to the LSD are not input.This D/A conversion output is monitored by the distortion meter 5, and then the A/A converter is connected. The fine adjustment variable resistor 3 of the MSB current source of the D converter is adjusted to minimize distortion. As shown in Figure 2 below, in the case of 16 bits, complete A/D-
The distortion or S/N in the input/output system of the D/A conversion system is about the number of bits x 6 dB + 2 dB, and in the case of 16-pit full scale, the S/N is 98 dB. Make adjustments to get closer to this. The lower the level of an audio signal, the closer it needs to be to this ideal level. MS here
Even if the level of distortion B is small, the distortion always accompanies it, so in the worst case, it worsens as shown by the dotted line in a. For this purpose, MS
Preciseness of B is the most important. The distortion of the second bit is when the input is 6.
If the dB decreases, the distortion will no longer occur and only the lower pits will become distorted one after another. In general, a D/A converter such as a ladder resistor requires more precision for the upper pit, and as long as the MSB is adjusted, there is no practical problem in digital conversion for audio.

Currently, in the conventional adjustment method, with 16 bits, the oscillator and distortion meter both have to be adjusted at 100 dB in order to measure close to 98 dB.
dB or more, and it took time to adjust the slight change, but in this example, the input level is shifted by 10 bits and the input level is lower than the P point, that is, 10×6 dB.
A 0 dB signal is input, and the output from the 16-bit D/A converter 4 is P' at full scale O dB. The distortion at this time is 38d
B becomes the limit value. For this reason, the distortion of the oscillator and the measurement system can be adjusted sufficiently if it is 38 dB or more. Furthermore, since the output level remains high, there is no risk of adjustment errors due to external noise. Naturally, the precision of the D/A converter is also improved, and adjustments can be made under normal conditions. These are useful because not only manual adjustment but also automatic adjustment by a robot or the like can be easily and accurately made.

(Effects of the Invention) According to the present invention, since the lower pit of the A/D converter is shifted to the upper level and D/A conversion is performed for adjustment, the noise of the measuring instrument system does not mislead the adjustment target. It can be done easily.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the present invention, and FIG. 2 is a diagram for explaining the vigilante level.

Claims (1)

[Claims] A/D conversion is performed by inputting a small AC signal that is several bits or less below the maximum input level as the center of the maximum input amplitude that can be converted into A/D.
D-convert the converted digital data, omit the inactive high-order bits except for the MSB, shift the low-order bits to the high-order bits, perform D/A conversion, and perform A/D conversion to minimize distortion of the output analog signal. An A/D converter adjustment device that adjusts the MSB level of the converter.