| 摘要 |
An active filter used in a phase-locked loop PLL comprises a passive integrator connected between an input and output of an inverting operational amplifier. As a consequence of this, fast pulses from a charge pump move directly to the amplifier. In accordance with the invention, a passive integrator (51) is placed before a non-inverting operational amplifier (52), whereby it short circuits the pulses of the charge pump to ground, and no additional low-pass filter is needed in front of the operational amplifier. Therefore, more low-pass filtering may be included in the passive integrator. The VCO tuning voltage area may be expanded by using a gain A>1 by shifting the DC level in the input of the operational amplifier (52). |
