JPH01198830A - Digital analog converter - Google Patents

Abstract

PURPOSE:To attain digital analog conversion through the use of the least distortion area in response to the level of an input signal by providing an adder applying an offset to an input digital signal and a digital analog converter. CONSTITUTION:With a maximum amplitude of an input digital signal 1 set to OdB and with the level of the signal 1 at -6dB or over, a level detection circuit 7 makes an offset value 71 zero. with the level of the signal 1 set to -12dB or over and less than -6dB, the offset 71 is set to -12dB and the offset 71 is set to -18dB with the level of the signal 1 set to -12dB. The signal being the sum of the offset 71 and the signal 1 by an adder 8 is given to a digital analog converter 5 and the offset 71 is inputted to the digital analog converter 6. Then output voltages of the converters 5, 6 are subtracted the subtractor 9. Thus, the digital analog conversion is applied by using the region with least nonlinearity in response to the signal level.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a digital-to-analog converter, and is particularly suitable for digital audio equipment in that it can reduce harmonic distortion and noise.

BACKGROUND OF THE INVENTION A digital-to-analog converter is an essential circuit component of digital audio equipment, and its performance has a large impact on the performance of digital audio equipment.

With reference to the drawings below, the conventional digital
An example of an analog converter will be explained.

FIG. 3 shows the basic configuration of a conventional digital-to-analog converter. In Fig. 3, 1 is an input digital signal, 2 is a current source that outputs a current corresponding to each bit of input digital signal 1, and 3 is an analog switch that turns on and off the output current of current source 2. , and has a control signal input 31 for controlling off. An x/v converter 4 converts the current obtained by the current source 2 and analog switch 3 into a voltage value, and outputs an analog voltage 41 corresponding to the input digital signal 1.

The operation of the digital-to-analog converter configured as described above will be explained below.

First, the current value output by current source 2 should be compatible with MSH! Then, the one corresponding to 28B is -j-I, 3
Those corresponding to 5B are 1/2 in order of ``Y''.
It has become. The analog switch 3 is turned on when each bit of the input digital signal 1 is "1" and turned off when it is "0". As a result, a current proportional to the value of the input digital signal 1 is input to the I/V converter 4, and is converted into a voltage value by the I/V converter 4. As a result, an analog voltage output 41 corresponding to the input digital signal 1 is obtained.

Next, the operation when each current source 2 has an error will be explained. First, the error of each current source 2 is calculated from Δ3 to Δ
. Then, as shown in Figure 3, the current values output by each current source 2 are in order from the one corresponding to the MSB! 10Δ3. T
I+Δ2. −jI+Δ1°, I+Δ. In this way, the input digital signal 1 when each current source 2 has an error is 0.
The relationship between the output analog voltage 41 and the output analog voltage 41 is shown in FIG. In FIG. 4, the gain of the I/V converter 4 is set to 1.

Generally the error is Δ3~Δ. is correlated with the absolute value of each current source 2. Therefore, as can be seen from FIG. 4, the nonlinearity of the output analog voltage is greatest in the portion where the MSB is inverted, followed by the nonlinearity associated with the inversion of 28B. In this way, the higher the pit, the greater the non-linearity caused by the bit inversion, and the lower the bit, the smaller the non-linearity caused by the bit inversion.

The distortion caused by the inversion of the MSB is generally called "zero cross distortion."

Problems to be Solved by the Invention In general, in digital audio, digital signals are recorded so that the offset is always constant regardless of the magnitude of the signal level.

Therefore, the MSB of the input digital signal is constantly inverted even when the signal level is very low.

However, in the above configuration, the nonlinearity is greatest when the MSB of the input digital signal is inverted. Therefore, regardless of the signal level, the region with the greatest nonlinearity is always used to This means that it is being converted to analog. Therefore, especially when the signal level is low, deterioration of sound quality and audio characteristics due to so-called "zero cross distortion" becomes a problem.

In view of the above problems, the present invention makes it possible to perform digital-to-analog conversion using an area with the least distortion depending on the level of an input signal.

Problems to be Solved In order to solve the above problems, the digital
The analog conversion device includes an adder that adds an offset to an input digital signal and a digital-to-analog converter, and the digital-to-analog converter converts the signal obtained by adding the offset to the input digital signal by the adder. It is composed of

Operation The present invention uses the above-described configuration to add an optimal offset to an input digital signal according to the signal level, and then performs digital-to-analog conversion using a digital-to-analog converter. This makes it possible to perform digital-to-analog conversion using the region with the least nonlinearity depending on the signal level, and can significantly improve waveform distortion, especially when the signal level is low. Can be done.

Embodiment Hereinafter, a digital-to-analog converter according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the circuit configuration of a digital-to-analog converter according to a first embodiment of the present invention. In FIG. 1, 1 is an input digital signal, 7 is a level detection circuit that outputs an offset value 71 according to the level of the input digital signal, 8 is an adder that adds the offset value 71 to the input digital signal 1, and 6.6 is an adder that adds the offset value 71 to the input digital signal 1. The digital-to-analog converter shown in FIG. 3 converts the input digital signal 1 plus the offset value 71 and the offset value 71 into digital-to-analog conversion and outputs them. e is a subtracter that subtracts the output analog voltage of the digital-to-analog converter H5,a and outputs an analog voltage 41 corresponding to the input digital signal 1.

The operation of the digital-to-analog converter configured as described above will be explained below with reference to FIGS. 1 and 2. First, in FIG. 2, a is the input digital signal 1,
b is the output analog voltage of the digital-analog converter 5, C is the output analog voltage of the digital-analog converter 6, and d is the output analog voltage 41 of the subtracter 9. First, when the maximum amplitude of the input digital signal 1 is odB, the level detection circuit 7 detects that the level of the input digital signal 1 is -6
When the level of input digital signal 1 is -12dB or more, -edBdB, the offset value 71 is set to zero when the level is more than dB
If the level of input digital signal 1 is less than -12 dB, the offset value 71 is -12 dB.If the level of input digital signal 1 is less than -12 dB, the offset value is 7.
1 is output as -18dB. Then, a signal obtained by adding the offset value 71 and the input digital signal 1 by the adder 8 is input to the digital-to-analog converter 6, and the offset value 71 is input to the digital-to-analog converter 6.

Therefore, the output waveforms of the digital-to-analog converter 5.6 for the input digital signal 1 shown in FIG. 2a are as shown in FIG. 2a.

By subtracting the output voltage of the digital-to-analog converter 6.6 using the subtracter 9, an analog voltage output 41 corresponding to the input digital signal 1 is obtained as shown in FIG. 2d.
get. As is clear from Figure 2, when the amplitude of the input digital signal 1 is less than -e dB, the MSB of the input signal to the digital-to-analog converter 6 is not inverted, and the amplitude of the input digital signal 1 is When it is less than -12 dB, the input signal of the digital-to-analog converter 6 has a MSB of 28 B.
is not reversed either. This shows that the digital-to-analog conversion is performed using the least nonlinear region of the digital-to-analog converter 6 according to the amplitude of the input digital signal 1.

In the above embodiment, the case where the value a is used as the possible value of the offset value 71 was explained, but if the level detected by the level detection circuit 7 is further divided into four or more possible values, , when the amplitude of the input digital signal 1 becomes even smaller than -12 dB, the bits below sSB of the input signal of the digital-to-analog converter 6 are converted from digital to analog without being inverted like the MSB and 28B. things become possible.

Further, in the above embodiment, the offset value 71 added by the adder 8
As a method for removing the offset value, a case has been described in which the offset value 71 is converted from digital to analog using another digital to analog converter 6, and then the offset component is removed using the subtracter 9. It is also possible to use a plurality of voltage sources corresponding to individual offset values in the converter 60s, switch the voltage sources according to the offset value, and send the voltage to the subtracter 9 to remove the offset component. .

The digital/analog converter of the present invention which converts digital/analog signals into digital/analog has more than the effects of the invention.
Equipped with an analog converter, it adds an optimal offset to the input digital signal according to the signal level, and then converts the digital
By performing analog conversion, it is possible to perform digital-to-analog conversion using the region with the least nonlinearity depending on the signal level, which can significantly improve waveform distortion, especially when the signal level is small. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a digital-to-analog converter according to the first embodiment of the present invention, FIG. 2 is a waveform diagram showing the relationship between each signal waveform in the first embodiment, and FIG. FIG. 4, which is a basic configuration diagram of a digital-to-analog converter, is a characteristic diagram of an output analog voltage with respect to an input digital signal in a conventional digital-to-analog converter. 2... Flow L 3... Analog switch, 4... I/Vl' converter, 5, 6...
...Digital-to-analog converter, 7...Level detection circuit, 8...Adder, 9...
Subtractor. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 4

Claims (2)

[Claims] (1) A digital-to-analog conversion device comprising: a digital-to-analog converter for converting a digital signal to an analog signal; and an adder for adding an offset to the digital signal input to the digital-to-analog converter. (2) The digital-to-analog converter according to claim 1, wherein the offset value is changed depending on the level of the input digital signal.