CHARGE PUMP CIRCUIT

PURPOSE:To operate the circuit at both high and low gain states by providing a high gain charge pump circuit employing a C-MOS analog switch and a low gain charge pump circuit employing a current switch circuit and switching the two charge pump circuits. CONSTITUTION:The high gain charge pump circuit 16H employs a C-MOS analog switch. Thus, in the high gain mode, the switching speed is high and the leakage current is small, then the output is very stable in the absence of the input. Moreover, the low gain charge pump circuit 16L uses a current switch comprising transistors TR1-TR4 and an NPN bipolar TR. Since the NPN TR has a large current driving force and the collector-base capacitance is small, the TR is controlled with high accuracy by a minute signal at a high frequency. Thus, the phase locking is obtained in an excellent way at both the high and low gain sides.