JP2658038B2 - Digital-to-analog converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital / analog converter for converting a PCM digital signal into an analog signal.

2. Description of the Related Art In recent years, digital-to-analog converters have been actively used in the field of digital audio. The digital-to-analog converter described here is a digital-to-analog converter.
It means a device of a digital-to-analog conversion part, including an analog converter.

Hereinafter, the above-described conventional digital-to-analog converter will be described with reference to the drawings.

FIG. 7 shows digital-to-analog conversion characteristics of a conventional digital-to-analog converter. In FIG. 7, U is a negative digital signal conversion characteristic, V is a positive digital signal conversion characteristic, β is a zero point of the conversion characteristic of U, α is a zero point of the conversion characteristic of V, and ξ is a conversion characteristic of U and V. , W, is a positive conversion characteristic at the time of the ideal digital / analog converter.

The reason why the offset value is generated in the digital-to-analog converter as described above will be described.

First, the PCM digital signal input to the digital-to-analog converter is the signal shown in FIG. However, a ladder-type resistor network system is well known as a commonly used digital-to-analog converter, and in recent digital audio devices, such a system and a current addition type system similar thereto are mostly used. . In particular, when such a digital-to-analog converter is used, the maximum error of the digital-to-analog converter occurs when the switch of the largest digit turns on and off. This is between the points α and β in FIG. 8, where an offset value of Δ is generated. (For example, “All about PCM Digital Audio”, Seibundo Shinkosha, pp. 39-41) Problems to be Solved by the Invention In the digital-to-analog converter as described above, the offset ξ exists. Therefore, there is a problem that the converted signal waveform is distorted. Also, this distortion has a greater effect as the input digital signal level is lower, and the distortion rate tends to be worse. FIG. 9 shows the U shown in FIG.
FIG. 9 is a diagram of a sine wave signal reproduction waveform η in the −V conversion characteristic.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a digital-to-analog converter in which the influence of an offset error of a digital-to-analog converter, which is conspicuous when the input digital signal level is low, is eliminated.

Means for Solving the Problems In order to solve the above-mentioned problems, a conversion characteristic aliasing detector for detecting the set aliasing point in order to perform aliasing conversion at the set aliasing point of the digital / input digital signal of the present invention; An input level discriminator for discriminating an input digital signal level and controlling a return operation of the conversion characteristic return detector when the input digital signal level is equal to or lower than a predetermined level; and a digital return circuit for returning a digital signal based on a detection signal of the conversion characteristic return detector. It comprises a signal folding circuit, a digital-to-analog converter for converting the folded digital signal into an analog signal, and an analog signal folding unit for folding the digital-to-analog converter output signal in an analog manner.

According to the present invention, when the input digital signal level is lower than a certain level and the error due to the offset value is large, the input digital signal is folded at the set folding point of the digital signal, and the analog signal after digital-to-analog conversion is obtained. By further folding the signal in an analog manner, a digital-to-analog conversion characteristic free from the influence of the offset value can be obtained, and an analog output signal free from the influence of the offset value can be obtained.

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

FIG. 2 shows the digital-to-analog conversion characteristics of the digital-to-analog converter according to one embodiment of the present invention. In FIG. 2, the conversion characteristics BY-X-A are the original digital-to-analog conversion characteristics and the conversion characteristics BY-
D is the digital-to-analog conversion characteristic when folded at Y, conversion characteristic CXA is the digital-to-analog conversion characteristic when folded at X, and ε is the offset value of the original digital-analog converter. It is.

FIG. 1 is a configuration diagram of one embodiment of the present invention. In FIG. 1, E is a digital input signal, 1 is a conversion characteristic aliasing detector, and 7 is an input level discriminator. When the level of a digital signal input to the level discriminator 7 is lower than a certain level, the level is determined. The conversion characteristic return detector 1 is controlled by the output signal of the discriminator 7 to operate. F is the output signal of the conversion characteristic return detector, 2 is the digital signal return circuit, G is the output signal of the digital signal return circuit, 3 is the synthesizer of the analog signal, H is the output signal of the synthesizer 3, 4 is the digital / analog signal. converter,
I is an output signal of the digital / analog converter, 5 is an analog signal looper, J is an output signal of the analog signal looper, 6 is an analog signal synthesizer, and K is an output signal of the synthesizer 6.

The operation of the digital-to-analog converter of FIG. 1 configured as described above will be described below with reference to FIGS.

Here, in order to simplify the description, an operation after the input level discriminator has determined that the input digital signal level is lower than a certain level will be described.

First, in FIG. 3, E indicates a 4-bit input digital signal, where the first bit is MSB and the fourth bit is LSB. L is a positive / negative signal when the signal zero of E is set to Y. Here, as one specific example, the operation when the digital signal is folded at the Y point will be described with reference to the configuration of FIG. The digital signal of E is detected by the conversion characteristic return detector 1 as "1" of the MSB. When the digital signal is "1", the digital signal return circuit 2 inverts the M signal and the L signal as shown in FIG. The negative signal portion of the signal is synthesized by the analog synthesizer 3 and applied to the digital / analog converter 4.
M of this analogized PAM (pulse amplitude modulation) signal
When the signal portion is looped back by the analog signal loopback unit 5, the result is as shown in FIG. 3N. Here, the F 'signal input to the analog signal loopback unit 5 is converted by the digital / analog converter, and then the conversion time of the digital / analog converter is set to operate the analog signal loopback unit 5. Delay processing. FIG. 4 shows this state for each signal sample of E. The reason why M16 = M15 is to prevent data overflow. FIG. 3, FIG.
FIG. 5 shows the configuration of one specific example of FIG. The numbers of the blocks shown here and the blocks of FIG. 2 having the numbers close to each other have basically the same function. (For example, 1 '= 1) Here, the -1 function of the block 2' is the MSB "1" of E
The digital signal in the area is inverted, and the value obtained by subtracting digital "1" from this value is -1.

FIG. 6 shows each signal of FIG. 5 with the E signal as a sine wave. here, Is the digital signal inversion of b, Analog signal inversion of digital signal inversion b.

As described above, according to the present embodiment, in the digital-to-analog converter, the conversion characteristic having the BYXA offset error of FIG. The conversion characteristics can be improved to eliminate the BYD offset error.

In the embodiments of FIGS. 3, 4, 5, and 6, the turning point is the Y point in FIG. 2, but may be the X point. FIG. 3 L, P, and FIG. 3 show the case of turning at the turning point X.
Q. Here, among the L positive / negative signals obtained by setting the X point of the input digital signal E to the signal zero point, the P signal is inverted when the MSB is "0". The P signal is converted from digital to analog and then converted to analog. When the P signal portion is folded back in an analog manner, it becomes a Q signal. Then, although not shown in FIG. 4, the processing is performed in the same manner as described above, and BY-Y shown in FIG.
The conversion characteristic of XA can be improved to the conversion characteristic of CXA in FIG.

In addition, the turning point is the same except for the points Y and X in FIG.
The conversion may be made at any point of the conversion characteristic in the MSB region. Similarly, as shown in FIG. 1, the value of the input signal level at which the folding operation is to be performed may be set by the input level discriminator 7, and processing at an arbitrary input level is possible. That is, the input level discriminator 7 or the K-bit discriminator 7 'equivalent thereto only needs to be able to detect a signal level range below the K bits of the input digital signal, and even monitors the K-th bit. You can see what you should do.

As described above, the present invention provides a conversion characteristic return detector that detects a set return point to perform return conversion at a set return point of an input digital signal, and determines an input digital signal level to be constant. An input level discriminator for controlling a folding operation of the conversion characteristic folding detector when the level is equal to or less than a level, a digital signal folding circuit for folding a digital signal based on a detection signal of the conversion characteristic folding detector, and a folded digital signal A digital-to-analog converter that converts the analog signal into an analog signal, and a digital signal loopback that loops back the digital-to-analog converter output signal in an analog manner.
When the input analog signal level is lower than a certain level and the error due to the offset value is large, the level can be determined to eliminate the offset error of the digital-to-analog converter and to obtain an analog output signal without the influence of the offset value. is there.

[Brief description of the drawings]

FIG. 1 is a block diagram of a digital-to-analog converter according to an embodiment of the present invention, FIG. 2 is a conversion characteristic diagram of the digital-to-analog converter according to the embodiment of the present invention, and FIGS. FIG. 5 is a data string diagram for explaining the operation in the embodiment of the figure, FIG. 5 is a block diagram showing a specific configuration in the embodiment of the present invention, FIG. 6 is a waveform diagram for explaining the operation in the embodiment of the present invention, FIG. FIG. 8, FIG. 9, and FIG. 9 are a characteristic diagram, a data string diagram, and a waveform diagram for explaining the configuration and operation of the conventional example. 1 ... Conversion characteristic return detector, 2 ... Digital signal return device, 5 ... Analog signal return device, 7 ... Input level discriminator.

Claims (1)

(57) [Claims] 1. A conversion characteristic return detector for detecting a set return point in order to perform return conversion at a set return point of an input digital signal, and said conversion characteristic return detector determines an input digital signal level when the input digital signal level is lower than a predetermined level. An input level discriminator for controlling a folding operation of the conversion characteristic folding detector, a digital signal folding circuit for folding a digital signal based on a detection signal of the conversion characteristic folding detector, and converting the folded digital signal into an analog signal A digital-to-analog converter, and an analog signal loopback for looping back the digital-to-analog converter output signal in an analog manner, wherein the digital-to-analog converter is configured to convert an input digital signal into an analog signal and output the analog signal. Analog converter.