JPH01174122A - Automatic input/output characteristic setting method in a/d converter - Google Patents

Abstract

PURPOSE:To prevent generation of waveform clip by obtaining a maximum value from a prescribed number of sampling data fetched from an A/D converter and calculating an input range to be set newly from the relation between the maximum value and the specified value. CONSTITUTION:In case of the setting the input/output characteristic in an A/D converter(Cut) 5, an automatic setting button 18 is depressed, a prescribed reference voltage setting data Dr is outputted to a reference voltage setting circuit 16 to bring an input voltage range of the Cut 5 to the specified value. Then the data outputted sequentially from the Cut 5 is fetched by a prescribed number as a sample data for a prescribed period and the maximum value is obtained from the fetched sample data. The maximum value and the specified value of the set input voltage range judges that how many bits can afford to remain and the input voltage range to be set newly is calculated. To set the new input range to the Cut 5, a required reference voltage setting data Dr is outputted to the circuit 16.

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention relates to an A/D converter applied to digital audio equipment such as a DAT (digital audio tape recorder), and in particular, it relates to an A/D converter that does not cause waveform clipping. The present invention relates to an input/output characteristic automatic setting method that can automatically set the input/output characteristics.

"Prior Art" Conventionally, an analog input circuit in a DAT has been configured as shown in FIG. In this figure, an analog input signal supplied from an external device (CD player, etc.) to the input terminal Tin is attenuated by a level adjuster (volume for adjusting recording level) l provided on the operation panel surface, and then The data is supplied to the A/D converter 2, converted into 16-bit digital output data by the A/D converter 2, and then supplied to the digital recording circuit 3.

The output of the level adjuster i is also supplied to a digital display type level meter 4 provided on the operation panel surface, and this level meter 4 displays the input level (recording level) to the A/D converter 2. It is now possible to do so. Here, if the display on the level meter 4 shows OdB, it means that the recording level is at the maximum limit, that is,
It is shown that the analog input signal has reached the upper limit of the input range of the A/D converter 2, and in this case, all 16 bits of the output data of the A/D converter 2 are valid full bits.

"Problem to be Solved by the Invention" By the way, when using the above-mentioned DAT to record a music source output from a CD player, for example, it is assumed that the level of the music source to be recorded is the highest before the actual recording. After selecting a portion and manually inputting the analog signal of that portion to the input terminal Tin, the level adjuster 1 is manually adjusted to set the recording level. In this case, in order to effectively utilize the dynamic range, it is necessary to adjust the display of the level meter 4 so that it can swing over the full scale from glossy to OdB. However, the display on the level meter 4 must never exceed OdB. This is because when the recording level exceeds the upper limit of the input range of A/D converter 2, the output data of A/D converter 2 becomes full bits, and the output data is distorted with the top of the original analog input signal waveform cut off. This is because the data corresponds to a different waveform, resulting in so-called waveform clipping. In order to prevent such waveform clipping, the recording level must be adjusted with great care, which poses a problem in that extremely complicated operations are required.

This invention was made in view of the above-mentioned circumstances, and provides a method for automatically setting input/output characteristics in an A/D converter that eliminates the need for any manual level adjustment of analog signals that was necessary to prevent waveform clipping. It is intended to.

"Means for Solving the Problems" The present invention provides an A/D converter that converts an analog input signal into digital data and whose input range can be arbitrarily set.
With the input range of the A/D converter set to the specified value,
An analog input signal to be converted is input to the A/D converter, a predetermined number of data sequentially output from the A/D converter is captured as sample data within a certain period of time, and among the predetermined number of sample data thus captured, A maximum value is calculated from the above, a new manual range to be set is calculated from the relationship between this maximum value and the specified value, and the new input range thus calculated is set to the A/D converter. .

"Effect" According to the method described above, just by inputting the portion of the analog input signal to be converted that is considered to have the highest level prior to the normal conversion operation, the input/output characteristics of the A/D converter can be changed to cause waveform clipping. This eliminates the need for level adjustment of the analog input signal, which was conventionally required to prevent waveform clipping.

"Embodiments" Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In this figure, a music source is supplied to the input terminal Tin from a CD player. 5 is the input terminal Tin
The analog input voltage signal Vin directly supplied from 16
This is a successive approximation type A/D converter that sequentially converts bits (DB+s to DB,) into digital output data. A successive approximation logic 7 that sequentially determines the most important bits DB+s-DBO of the output data based on the output of the comparator 6, and each bit DB, -DBO of the output data output from the successive approximation logic 7. From a D/A converter 8 that generates an output voltage Vr corresponding to the weight (
& has been completed. This A/D converter 5 is
The reference voltage V, r input to the internal D/A converter 8
The analog input voltage range is set according to ef, and when the analog input voltage Vin corresponding to the upper limit of this input voltage range is input, the output data becomes full bits, and each bit D B Is”D
All B o's are "l".

The 16-bit output data sequentially output from the A/D converter 5 described above is supplied to the digital recording system circuit 3 via the DSP (digital signal processing processor) 1O, and is then sent to the data modulation circuit 13, recording amplifier 14, and Magnetic recording is performed on a DAT magnetic tape via the magnetic head 15.

i6 is a reference voltage setting circuit, and based on the 8-bit range setting data Dr supplied from the DSP 10,
The reference voltage V ref supplied to the /D converter 5 is set to 25
6 (=2'') stage. Also, 18 is an automatic setting button, which is used to instruct the DSP 10 to start automatic setting processing, which will be described later.

The DSP to is a one-chip microcomputer that executes digital signal processing algorithms at high speed, and its built-in memory stores the following automatic settings based on the output data of the A/D converter 5. A program for executing processing is stored in advance.

(2) When the automatic setting button 18 is pressed, predetermined reference voltage setting data Dr is output to the reference voltage setting circuit 16 in order to set the input voltage range of the A/D converter 5 to the specified value. In this case, the specified value is a value corresponding to the upper limit value (defined as 2 V rl118 by the standard) of an analog signal output from a CD player having the highest level as a music source.

(2) A predetermined number of data outputted from the A/D converter 5 as sample data are taken in within a certain period of time, and the maximum value is determined from among the predetermined number of sample data taken in.

(2) From the maximum value obtained in (2) above and the specified value of the input voltage range set in (2) above, determine how many bits remain, and from this, calculate the input terminal range to be newly set. For example, if the maximum value of sample data is 13
If it is bit full, there is a margin of 3 bits remaining, and the value obtained by adding the value for 3 bits to the above specified value becomes the new input voltage range.

■Reference voltage setting circuit to set a new input range to A/D converter 5! The required reference voltage setting data Dr is output to 6.

Next, in the above-described embodiment, when recording a music source output from a CD player, prior to actual recording, a portion of the music source to be recorded that is considered to have the highest level is selected, and that portion of the music source is selected. Input the analog signal to the input terminal Tin and press the automatic setting button 18. Then, the DSPIO sets the input voltage range of the value corresponding to the supplied analog input voltage Vin to the A/D converter 5 in accordance with the above-mentioned steps ① to ②. As a result, A/D
The input/output characteristics of converter 5 are automatically set so that waveform clipping does not occur.

"Effects of the Invention" As explained above, according to the present invention, prior to the regular conversion operation, the analog input signal to be converted is set to the A/D converter's input range at a specified value. /D converter, and within a certain period of time,
A predetermined number of data sequentially output from the D converter is taken in as sample data, the maximum value is determined from among the predetermined number of sample data taken in, and a new input range to be set is determined from the relationship between this maximum value and the specified value. is calculated and the new input range obtained is set in the A/D converter. Therefore, before the regular conversion operation, input the part of the analog input signal to be converted that is considered to have the highest level. By simply doing this, the input/output characteristics of the A/D converter are automatically set to prevent waveform clipping, which eliminates the need for level adjustment of the analog input signal, which was previously required to prevent waveform clipping. This effect can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 2 is a block diagram showing the configuration of an analog input circuit of a conventional DAT. 5... Successive approximation type A/D converter, 10...
...DSP, 16...Reference voltage setting circuit,
18... Automatic setting button.

Claims (1)

[Claims] In an A/D converter that converts an analog input signal into digital data and allows the input range to be set arbitrarily, the input range of the A/D converter is set to the specified value before the conversion is performed prior to the regular conversion operation. A predetermined number of data sequentially outputted from the A/D converter is inputted into the A/D converter, and a predetermined number of data sequentially outputted from the A/D converter is captured as sample data, and the maximum The A/D converter is characterized in that the input range to be newly set is calculated from the relationship between the maximum value and the specified value, and the new input range thus calculated is set in the A/D converter. A method for automatically setting input/output characteristics in a D converter.