| 摘要 |
PURPOSE:To reduce the output offset, by setting a phase comparing part to a B- or AB-class operation to reduce the bias current while no signal is delivered as well as to reduce the peak current of the input signal. CONSTITUTION:Each working current of transistors (TR)Q17 and Q18 in current mirror circuits CM1 and CM2 which serve also as differential amplifiers of a phase comparing part 12 operates an AB- or B-class operation in which the peak current on the input signal supplied from an input signal source for phase to be compared is reduced by a bias part 11. As a result, the mean value of an output current is set at zero through an LPF in case when the frequency of a switching signal is higher than the frequency of the input signal for phase to be compared. Thus the unbalance of a current mirror circuit CM3 comprising TRS Q23 and Q24 emerges int the form of an unbalance component of an output current waveform to be changed into a waveform having the upper and lower parts asymmetric to each other. This error component is turned into an output offset. In this case, a large DC current does not flow due to the AB- or B-class operation, and accordingly the output offset can be reduced by a degree equivalent to the DC current. |
