JPH05327511A - Digital/analog converter - Google Patents

Abstract

PURPOSE:To cancel the distortion of a pulse rising and falling, and to attain a D/A converter whose distortion can be reduced by smoothing a pulse signal equivalent to the positive number and negative number of a digital input signal, and operating an antiphase-addition. CONSTITUTION:A pulse width modulator 5 generates a pulse wave when the digital input signal is the positive number, and outputs a pulse wave 0 when the digital input signal is not the positive number. On the contrary, a pulse width modulator 6 outputs the pulse wave when the digital input signal is the negative number, and outputs the pulse wave 0 when the digital input signal is not the negative number. At that time, a constant phase relation between a pulse width center and a timing signal can be always attained, so that a waveform distortion due to a phase component can not be generated at the output waveform of the modulators 5 and 6. And also, a symmetrical relation between the pulse signal of a positive polarity and the pulse signal of a negative polarity can be attained by using a zero reference level as a center by the anti-phase-addition, so that a secondary harmonic wave distortion can not be generated. Therefore, the high frequency components of the outputs of the modulators 5 and 6 are removed by smoothing filters 7 and 8, and a smooth waveform is inputted to an antiphase-adder 9. Thus, the distortion of the rising and falling of the pulse wave can not be generated, and only a basic waveform can be outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital / analog converter (hereinafter referred to as D / A converter) for converting a digital signal into an analog signal, and more particularly to pulse width modulation (hereinafter referred to as PWM).
Called)) is used.

[0002]

2. Description of the Related Art As one method of D / A conversion, a digital signal to be converted is converted into a pulse width signal having a pulse width responsive to the data value thereof, and then passed through a smoothing filter to demodulate into an analog signal. There is known a method of doing so, and by using this method, highly accurate D / A conversion can be performed without using highly accurate parts in a circuit.

A conventional D / A converter will be described below with reference to the drawings. FIG. 3 is a block diagram of a conventional D / A converter. In the figure, reference numerals 1 and 2 denote pulse width modulators, which generate pulse width signals having a pulse width corresponding to a digital input signal value and a pulse width corresponding to a complement value of the digital input signal value, respectively, in synchronization with a timing signal. Occur. Reference numeral 3 denotes an anti-phase adder, which inverts the phase of the waveform input to the-terminal with respect to the waveform input to the + terminal, adds the waveform, and outputs the result. Reference numeral 4 is a smoothing filter.

Next, in explaining the operation of FIG. 3, waveforms of respective parts when the digital input signal value is 11 values of -5 to +5 are shown in FIG. Output A of pulse width modulator 1
Becomes a pulse width signal having a pulse width corresponding to the digital input signal value. The output B of the pulse width modulator 2 becomes a pulse width signal having a pulse width corresponding to the complement of the digital input signal value. The output C in which the pulse waves A and B are added in anti-phase has a center position of the pulse width thereof which has a constant phase relationship with the timing signal, and a positive pulse signal and a negative pulse centered on the zero reference level. It has a symmetrical relationship with the pulse signal.

Since the center position of the pulse width always has a constant phase relationship with the timing signal, waveform distortion due to the phase component does not occur. Further, since the positive polarity pulse signal and the negative polarity pulse signal are symmetrical with respect to the zero reference level, the second harmonic distortion due to the asymmetry of the pulse signal is suppressed. As a result, an analog signal without distortion is output to the output of the smoothing filter 4.

[0006]

However, in the above configuration, since the slew rate of the operational amplifier normally used as the anti-phase adder 3 is finite, the pulse waves A and B are
However, there is a problem that when the pulse is added in the opposite phase, a new distortion is generated at the rising and falling edges of the pulse.

The present invention solves the above problems.
The present invention provides a D / A converter that does not generate waveform distortion and second harmonic distortion due to a phase component, and does not generate distortion at the rising and falling edges of a pulse.

[0008]

In order to achieve this object, a D / A converter according to the present invention has a pulse width having a predetermined pulse width when a digital input signal taken in in synchronization with a timing signal is a positive number. A first pulse width modulator for converting to a signal, a second pulse width modulator for converting to a pulse width signal having a predetermined pulse width when the digital input signal is a negative number, and the first pulse width modulator From the first filter that smoothes the output of the second pulse width modulator, the second filter that smoothes the output of the second pulse width modulator, and the anti-phase adder that outputs the difference between the outputs of the first and second filter It is configured.

[0009]

With the above configuration, since the pulse width signals corresponding to the positive and negative numbers of the digital input signal are smoothed and the antiphase addition is performed, the distortion at the rising and falling edges of the pulse can be canceled. D / with little distortion
A conversion can be performed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a D / A converter according to the present invention. In FIG. 1, reference numerals 5 and 6 are pulse width modulators, which convert a digital input signal that is taken in in synchronization with a timing signal into a pulse width signal having a predetermined pulse width. Reference numerals 7 and 8 are filters for smoothing the output of the pulse width modulator. 9 is an anti-phase adder.

The operation of the D / A converter of the present embodiment constructed as above will be described below. FIG. 2 shows an output waveform of the pulse width modulator when the digital input signal value is 11 values from -5 to +5. When the digital input signal is given, the pulse width modulators 5 and 6 generate pulse waves having a pulse width according to the input value. The pulse width modulator 5 generates a pulse wave only when the digital input signal is a positive number (+1 to +5), and outputs a pulse wave 0 when the digital input signal is other than that (-5 to 0). The pulse width modulator 6 generates a pulse wave only when the digital input signal is a negative number (−5 to −1), and outputs a pulse wave 0 otherwise (0 to +5). Here, in the output waveform of the pulse width modulator, since the center position of the pulse width always has a constant phase relationship with the timing signal, the waveform distortion due to the phase component does not occur. In addition, since the positive-polarity pulse signal and the negative-polarity pulse signal have a symmetrical relationship with the zero reference level as the center by performing the anti-phase addition, the second harmonic distortion caused by the asymmetry of the pulse signal also occurs. do not do. Next, the outputs of the pulse width modulators 5 and 6 are
Since high frequency components are removed by the smoothing filters 7 and 8, respectively, a smooth waveform is input to the anti-phase adder 9. Therefore, distortion due to rising and falling of the pulse wave does not occur, and only the fundamental wave is output.

In the present embodiment, the anti-phase adder 9
It goes without saying that a smoothing filter may be further connected to the output of the.

[0014]

As described above, according to the present invention, when the digital input signal taken in in synchronization with the timing signal is a positive number, it is converted into a pulse width signal having a predetermined pulse width.
A pulse width modulator for converting the digital input signal into a pulse width signal having a predetermined pulse width when the digital input signal is a negative number;
Pulse width modulator, a first filter that smoothes the output of the first pulse width modulator, a second filter that smoothes the output of the second pulse width modulator, and the first and second filters. Since the output of the anti-phase adder that takes the difference of the filter output of and is output is the D / A converter output, the second harmonic distortion is generated without the distortion caused by the rise and fall of the pulse wave. It has an excellent effect that the above can be suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a D / A converter according to the present invention.

2 is an output waveform of the pulse width modulator in FIG.

FIG. 3 is a block diagram showing a conventional D / A converter.

FIG. 4 is an output waveform of each part in a conventional D / A converter.

[Explanation of symbols]

 1, 2, 5, 6 Pulse width modulator 3, 9 Anti-phase adder 4, 7, 8 Smoothing filter

Claims (1)

[Claims] 1. A first pulse width modulator for converting a digital input signal, which is taken in synchronization with a timing signal, into a pulse width signal having a predetermined pulse width when the digital input signal is a positive number, and the digital input signal is a negative number. At this time, a second pulse width modulator for converting into a pulse width signal having a predetermined pulse width, a first filter for smoothing the output of the first pulse width modulator, and a second pulse width modulator A digital / analog converter comprising a second filter for smoothing an output and an anti-phase adder for taking a difference between outputs of the first and second filters and outputting the difference.