| 摘要 |
PURPOSE:To prevent C/N from being deteriorated and to prevent modulation distortion from being generated by composing a charge pump circuit of a constant current source and switching circuit, which switches the output current of the constant current source, and charging or discharging a loop filter with a constant current corresponding to phase difference. CONSTITUTION:An FET (Q3) is provided to charge a loop filter 6 by the constant current and an FET (Q6) is provided to discharge the loop filter by the constant current. The charge/discharge of these FETs (Q3, Q6) is controlled by phase comparing outputs U and D through FETs (Q4, Q5) for switching. Thus, a voltage E6 linearly proportional to phase difference DELTAtheta between signals R and V can be obtained from the filter 6. For example, the loop gain of a PLL can be adjusted by turning ON/OFF a transistor Q9 and changing intensity of a current i1 to be made flow to a terminal T1. Accordingly, by controlling this loop gain, the look-up time of the PLL can be shortened. |
