Output circuit

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Now, a basic circuit structure employed in of the present invention will be described with reference to FIG.
2.
A D/A converter 100 is a monopolar current output type D/A converter having one current output terminal 10 and operated with a power supply voltage V.
sub.
DD and a reference voltage e.
g.
ground potential.
In the remainder of the speech output circuit according to the present invention are included insulated gate field effect transistors (IGFET's) of the same conductivity (N-channel) type Q.
sub.
3, Q.
sub.
4, Q.
sub.
5 and Q.
sub.
6, having resistances sufficiently small as compared to the internal resistance of the D/A converter 100.
The D/A converter 100 is not specifically limited to any particular type and, for instance, a D/A converter as fully disclosed in U.
S.
Pat.
No.
4,055,773 could be conveniently used in the speech output circuit according to the present invention.
At first, when the current polarity control terminal 11 is at "0" level, the transistors Q.
sub.
3 and Q.
sub.
6 are turned OFF.
While the output of the inverter 12 is at a "1"-level, the transistors Q.
sub.
4 and Q.
sub.
5 are turned ON.
Therefore, a current defined by the monopolar current output type D/A converter 100 flows through the terminal 16, the transistor Q.
sub.
5, the terminal 13, the loudspeaker 15, the terminal 14, the transistor Q.
sub.
4, the current output terminal 10 and the D/A converter 100 and thereby the speaker 15 is driven in one direction.
Subsequently, when the current polarity control terminal 11 changes in potential to a "1" level, the transistor Q.
sub.
3 and Q.
sub.
6 are turned ON, while the transistors Q.
sub.
4 and Q.
sub.
5 are turned OFF, so that a current defined by the monopolar current output type D/A converter 100 flows through the terminal 16, the transistor Q.
sub.
6, the terminal 14, the loudspeaker 15, the terminal 13, the transistor Q.
sub.
3, the current output terminal 10 and the D/A converter 100 and thereby the loudspeaker 15 is driven in the opposite direction by the current flowing through the loudspeaker 15 in the reversed direction with respect to the preceding period