PURPOSE: To reduce the number of pins of a bipolar semiconductor integrated circuit by forming a switching circuit with a diode bridge composed of 4 diodes and two constant current sources so as to eliminate the need for an externally fitted MOS transistor(TR).
CONSTITUTION: When a current flows to constant current sources 20, 21 a phase comparison output current from the output terminal 6 of a computing element 1 flows to a sample-hold capacitor 16 from an output terminal 18 via a diode bridge switching circuit composed of diodes 22-25. On the other hand, when no current flows to the constant current sources 20, 21, the switching circuit is opened and a voltage across the capacitor 16 is held. Thus, the switching circuit is formed by the diode bridge to eliminate the need for an expensive externally fitted MOS, TR, thereby decreasing the number of pins of the bipolar semiconductor integrated circuit.
ITO TETSUO
SHIBAYAMA TOYOHIRO
