JPH0622334B2 - DA converter circuit - Google Patents

Description

The present invention relates to a DA converter circuit, and more particularly to a current output type DA converter circuit that outputs an analog signal centered on a midpoint current.

[Conventional technology]

Conventionally, in this type of DA converter circuit, a midpoint current is always passed and an AC signal is output centered on the midpoint current. The current output type DA converter circuit uses a DC voltage source connected to its output terminal as a load to convert the current flowing through this output terminal into an analog signal.

[Problems to be solved by the invention]

However, since such a DA converter circuit always supplies a midpoint current even when there is no signal, it consumes an unnecessary current.

This problem can be solved by making the midpoint current of the DA converter zero when there is no signal, but when the DA converter output current changes from zero to the midpoint current or from the midpoint current to zero, the analog signal Pulsed noise is generated in the output. This causes a feeling of hearing when driving the speaker with the analog signal output of the DA converter.

[Means for solving problems]

The DA converter circuit of the present invention includes a binary up / down counter that outputs a count signal that linearly changes the output current of the DA converter between zero and a midpoint current, and the count signal and external input data from the counter. And a switching circuit for selectively inputting to the DA converter, holding the output current of the DA converter at zero when there is no signal, and counting up by the switching circuit when the DA converter is operating. After selecting a signal, it is switched to the external input data, the external input data is selected by the switching circuit and then switched to the counting signal down-counted by the counter, and an analog signal is output centered on the midpoint current. is there.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 1 and FIG. 3 showing an embodiment of the present invention, 1LSB, 2LSB, 4LSB, and 8LSB are current output type DA converters 101 having a 4-bit structure. Send out. DA
The output current of the converter 101 is the reference voltage V
Set by _REF . The DA converter input switching circuit 103 outputs D based on the DA converter input switching signal 104.
Input data I1, I2, I3, I to the A converter 101
4 or enter the binary up / down counter 105
Select whether to input the count signal from. When the input data is "8", the DA converter 101 outputs the midpoint current. In order to eliminate unnecessary midpoint current flowing through the DA converter 101 when there is no signal, the DA converter input switching signal 10
Set 4 to high level, and binary up / down counter 1
The output of 05 is input to the DA converter 101. At this time, the content of the binary up / down counter 105 is set to the count value “0”. When the DA converter is operating, the counter 105 is counted up as shown in FIG. 3, and when the content of the counter 105 reaches the count value “8”, the counter is stopped and the DA converter input switching signal 104 is set to the low level. And inputs the input data I1 to I4 into the DA converter 101. The DA converter 101 outputs the waveform data of the input data I1 to I4, and when the waveform data is lost and there is no signal, the DA converter input switching signal 104 becomes high level. Then, the counter 10
5 counts down from the count value "8" and stops counting when the count value becomes "0".
Wait until the converter 101 operates. DA converter 1
The output of 01 has a DC cutting capacitor and outputs only an AC signal. However, if the output current is linearly increased and decreased by the counter 105 in an appropriate time, noise will not occur in the analog signal. it can.

Referring to FIG. 2 and FIG. 4 showing another embodiment of the present invention, 1LSB, 2LSB and 4LSB are current output type DA converters 201 of 3 bits respectively.
202, which are connected in parallel to the output terminal 203. The output currents of the DA converters 201 and 202 are set by the reference voltage V _REF . The DA converter input switching circuit 204 uses the DA converter input switching signal 20.
5, it is selected whether the code, I1 to I3, or the count signal from the binary up / down counter 206 is input to the DA converters 201 and 202 as input data. In this embodiment, when the sign of the input data is "0", the outputs of the AND gates 209, 210 and 211 are "0" and the output current of the 3-bit DA converter 201 is zero. On the other hand, 3-bit DA converter 202
When the bits I1 to I3 of the input data are "0", (1
LSB + 2LSB + 4LSB) is output, and the output current becomes zero when the input data I1 to I3 is "7". Further, when the reference numeral 203 is “1”, the OR gates 212 and 21
The output of 3,214 becomes "1", and the DA converter 20
The output current of 2 outputs the midpoint current of (1LSB + 2LSB + 4LSB), and the output current from the DA converter 201 for the input data I1 to I3 is added to this. The content of the binary up / down counter 206 is set to the count value “7”, and the DA converter input switching signal 205 is set to the high level to set the binary up / down counter 206.
Is output to the DA converters 201 and 202. D
When the A converter is operating, as shown in FIG.
06 counts down and stops counting when the count content becomes "0", and DA converter input switching signal 20
5 is set to low level and the signs of the input data, I1 to I3, are input to the DA converters 201 and 202. The DA converters 201 and 202 output the sign of the input data and the waveform data of I1 to I3, and when the waveform data is lost and there is no signal, the DA converter input switching signal 205 becomes high level. Subsequently, the counter 206 counts up from the count value "0", stops counting when the count content becomes "7", and waits in this state until the DA converters 201 and 202 operate next time. In this embodiment, the linearity error near the midpoint current output is due to the DA converter 201,
It is possible to expect another effect that the waveform distortion at the time of outputting an analog signal having a minute amplitude is not affected by an increase in the number of bits of 202 and is not increased as compared with the configuration of the embodiment shown in FIG.

In order to improve the accuracy of the analog signal output from the DA converters in the above embodiments, the number of bits may be increased.

〔The invention's effect〕

As described above, according to the present invention, the power consumption is reduced by preventing the midpoint current from flowing when the DA converter is not operating and allowing the midpoint current to flow only when the DA converter is operating. can do. This is particularly effective when using batteries. Also, DA
Using a binary up / down counter to linearly increase the current to flow the midpoint current of the converter and decrease the linear current to turn off the midpoint current hinders integrated circuit integration. It is possible to output an analog signal that does not include noise.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, FIG. 3 is a diagram for explaining the operation of FIG. 1, and FIG. It is a figure explaining operation | movement of FIG. 101, 201, 202 ... DA converter, 103,
204 ... DA converter input switching circuit, 105, 20
6 ... Binary up / down counter.

Claims (1)

[Claims] 1. A binary up / down counter that outputs a count signal that linearly changes the output current of a DA converter between zero and a midpoint current, and selectively outputs the count signal from the counter and external input data. And a switching circuit for inputting to the DA converter,
The output current of the A converter is maintained at zero, and the DA
When the converter operates, the switching circuit selects the count signal up-counted by the counter and then switches to the external input data, and the switching circuit selects the external input data and then down-counts the counter signal. A DA converter circuit characterized by switching and outputting an analog signal centered on a midpoint current.