JPH09232958A - Da converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DA converter which never excerts a bad influence upon the quality of a reproduced sound by eliminating power consumption between a PWM(pulse width modulation) signal generating part and a low-pass filter. SOLUTION: In the DA converter in which digital data is converted into the PWM signal of different pulse width, and the PWM signal is inputted to the low-pass filter 12, and an analog signal is outputted, the impedance converter 13 of FET configuration is installed between the output of the PWM signal generating part 23 and the low-pass filter 12, and the PWM signal is inputted to the low-pass filter 12 through the impedance converter. Since the impedance converter 13 of the FET configuration has very large input impedance, the power consumption between the PWM signal generating part 23 and the low- pass filter 12 can be eliminated, and in addition, since output impedance is low, current supply capacity to the low-pass filter 12 can be increased, and the stable transmission of the signal becomes possible, and the quality of the reproduced sound is never badly influenced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DA converter, and more particularly to a digital data PWM with different pulse widths.
The present invention relates to a DA converter that converts a signal into a signal, inputs the PWM signal into a low-pass filter, and outputs an analog signal.

[0002]

2. Description of the Related Art A so-called 1-bit DA converter of the ΔΣ (delta-sigma) system, which is most frequently used at present, is sampled by an oversampling filter before inputting digital data to a noise shaping circuit (ΔΣ modulator). Increase the conversion frequency. Next, the ΔΣ modulator equipped with a 1-bit quantizer performs noise shaping processing on the digital data output from the oversampling filter to reduce the quantization noise spectrum in the audible band, and a PWM DA converter. To enter.
The PWM DA converter generates a PWM signal having a pulse width corresponding to the digital data based on the input signal,
The PWM signal is input to the low pass filter, and the analog signal corresponding to the digital data is output from the low pass filter.

FIG. 3 is a block diagram showing the principle of a ΔΣ DA converter. Reference numeral 1 is a 1-bit resolution DA converter that outputs 1 or 0 according to an input signal. For example, as shown in FIG. 1 is output in the above case, and 0 is output if less than 0.5. 2
Is a delay unit for delaying the input signal for one sampling period, 3 is a first arithmetic unit for adding the digital input and the output of the delay unit, 4
Is a second calculation unit that calculates the output difference between the DA converter output and the first calculation unit. If a DC component of 0.25 is input as a digital input, the digital values and analog values at points A, B, and C The output changes every sampling cycle as shown in FIG. 5, and the same pattern is repeated every four sampling cycles. Focusing on analog output, 4
Since 1 is output only once in the sampling period, the analog output is passed through a low pass filter to obtain 0.25.
The DC component of can be output. Similarly, for any digital value input, an analog signal corresponding to the digital value can be output.

By the way, the above method has a poor resolution. Therefore, at present, the DA converter is operated at a speed higher than the sampling frequency, and an analog signal having a pulse width corresponding to the digital input value is output from the DA converter 1 to improve the resolution. That is, in FIG. 3, the DA converter 1 is 1 / N of the sampling period Ts.
Of the digital input in the cycle (= Ts / N) and outputs the same, each of the calculation units 2 and 3 performs calculation in the cycle of Ts / N, and the delay unit 2 from the second calculation unit 4 It operates to delay the input numerical value by Ts / N and output it. By doing so, the DA converter 1 can output an analog signal having a pulse width corresponding to the digital input value for each sampling period. For example, if N = 4 and 1.0, 0.75, 0.5, and 0.25 are input as digital inputs, 1 is always output from the DA converter 1 when the digital input is 1.0, as shown in FIG. 0.75
In the case of, 1 is output only 3 times in 4 times, in the case of 0.5, 1 is output only 2 times in 4 times, and in the case of 0.25, 1 is output only once in 4 times. That is,
An analog signal having a pulse width according to the digital input value is output from the DA converter 1. Therefore,
By passing this DA converter output through a low-pass filter, 1.0, 0.75, 0.5, and 0.25 analog signals are obtained, respectively.

Such a ΔΣ type DA converter is relatively easy to be integrated into an IC because of its configuration, and the PWM
Low-pass filter that converts signals to analog signals is also OP
It is possible to integrate by realizing with an active filter using an amplifier, and it has an advantage that it can be integrated with a very high degree of integration. For this reason, it has come to be widely used in accordance with the trend toward miniaturization of CD players and the like.

[0006]

SUMMARY OF THE INVENTION PWM (Pulse Width)
Assuming that the circuit connected to the low-pass filter is in an ideal state (input impedance is infinite) and there is no power consumption at all, the low-pass filter (active filter using an OP amplifier) provides a complete analog signal. It can be converted into a signal. However, in reality, such an ideal circuit and element do not exist, and power consumption occurs. In such a case, the active filter using the OP amplifier has a drawback that the ability to supply a current to the next circuit connected to the output is reduced particularly at a low frequency, which adversely affects the reproduced sound quality. . In view of the above, an object of the present invention is to provide a DA converter that can eliminate power consumption between the PWM signal output section and the low-pass filter and that does not adversely affect the reproduced sound quality.

[0007]

According to the present invention, there is provided a DA converter for converting digital data into PWM signals having different pulse widths, inputting the PWM signals to a low pass filter and outputting analog signals. An impedance converter having a FET structure is provided between the PWM signal generator and the low-pass filter, and the PWM signal is input to the low-pass filter via the impedance converter. The impedance converter having the FET configuration eliminates power consumption between the PWM signal generator and the low-pass filter because the input impedance is close to infinity, and moreover, the current supply capability to the low-pass filter can be increased because the output impedance is low. Stable signal transmission is possible and reproduction sound quality is not adversely affected.

[0008]

1 is a block diagram of a DA converter of the present invention. In the figure, reference numeral 11 denotes a digital processing unit which converts input digital data into PWM signals having different pulse widths and outputs the PWM signals. Reference numeral 12 denotes a low-pass filter (OP amplifier) which inputs the PWM signals and outputs an analog signal corresponding to the digital data. Is an active filter), 13 is P
It is an impedance converter having a FET configuration provided between the digital processing unit 11 that outputs a WM signal and the low-pass filter 12. Although only the L channel side is shown in the figure, an impedance converter and a low-pass filter are also provided on the R channel side.

The digital processing unit 11 is an IC,
It has an interpolation unit (oversampling unit) 21, a noise shaper calculation unit 22, and a PWM signal generation unit (PWM DA converter) 23. The interpolator 21 inserts the digital data between the input digital data by an interpolation method such as linear interpolation to raise the sampling frequency, and the noise shaper calculation unit 22 performs noise shaping processing on the input digital data to make it audible. Reduce the quantization noise spectrum in the band. The PWM signal generator 23 generates and outputs a PWM signal having a pulse width according to digital data from the signal output from the noise shaper calculator 22. The noise shaper calculation unit 22 and the PWM signal generation unit 23 specifically have the configurations shown in FIG.

PWM output from the digital processing unit 11
The signal is the FET 13 that constitutes the impedance converter 13.
Input to the gate of a via the resistor 13b. The input impedance of the impedance converter 13 is very large (close to infinity). For this reason, power consumption between the PWM signal generator 23 and the low-pass filter 12 can be eliminated, and since the output impedance of the impedance converter 13 is low, the ability to supply current to the low-pass filter 12 can be increased and stable signal transmission can be achieved. It is possible to prevent the reproduction sound quality from being adversely affected. From the above, even if the digital processing unit 11 is designed as a digital IC without considering the matching with the next stage, the impedance converter 13
By providing the power consumption, the power consumption can be eliminated, and the current supply capability to the low-pass filter 12 can be increased to enable stable signal transmission.

FIG. 2 is a block diagram of another embodiment of the present invention.
The difference from the embodiment of FIG. 1 is that the impedance converter 13
Between the low-pass filter 12 and the low-pass filter 12, an energy holding circuit 14 including a coil L, a capacitor C, and a diode D.
That is the point. In order to improve the reduction of the energy supply capacity to the low pass filter 12, the second embodiment further includes an energy holding circuit having a coil L having a function of storing electric energy as magnetic energy. In order to supply sufficient electric energy to the coil L, the source terminal of the FET 13a having a very large input impedance (close to infinity) is connected in principle, and the FET is
Input the PWM signal to the gate terminal of. With such a configuration, the current supply capability is improved, and thereafter, a desired analog signal can be output by passing through the low-pass filter 12 realized by an OP amplifier or the like. As described above, the present invention has been described with reference to the embodiments. However, the present invention can be variously modified in accordance with the gist of the present invention described in the claims, and the present invention does not exclude these.

[0012]

As described above, according to the present invention, the digital data is converted into PWM signals having different pulse widths, the PWM signals are input to the low-pass filter, and the analog signals are output.
In the A converter, an FET-type impedance converter having a very large input impedance is provided between the PWM signal output section and the low-pass filter, and the PWM signal is input to the low-pass filter via the impedance converter. The power consumption between the signal generator and the low-pass filter can be eliminated, and the output impedance of the impedance converter is low, so the current supply capacity to the low-pass filter can be increased, stable signal transmission is possible, and the reproduction sound quality is adversely affected. It is possible to provide a DA converter that does not affect

[Brief description of drawings]

FIG. 1 is a DA converter according to a first embodiment of the present invention.

FIG. 2 is a DA converter according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a ΔΣ type DA converter.

FIG. 4 is an explanatory diagram of an output signal of a DA converter.

FIG. 5 is an operation explanatory diagram of a ΔΣ type DA converter.

FIG. 6 is an explanatory diagram of a PWM system.

[Explanation of symbols]

 11-Digital processing unit 12-Low pass filter 13-Impedance converter 13a-FET 21-Interpolation unit (oversampling unit) 22-Noise shaper calculation unit 23-PWM signal generation unit

Claims (1)

[Claims] 1. A digital data PW having different pulse widths.
In a DA converter that converts an M signal and inputs the PWM signal to a low-pass filter to output an analog signal, an impedance converter having a FET structure is provided between the PWM signal output section and the low-pass filter, and the PWM signal is converted into the impedance converter. A DA converter characterized by inputting to a low-pass filter via.