PLL Loop Filter Sampling to Minimize Charge Pump Leakage Ripple

The patent implements periodic sampling of the charge pump output by the loop filter through controlled opening and closing of switches. The loop filter is connected to the charge pump output only during specific phases (when UP or DOWN signals are active) and disconnected during other phases, converting continuous connection into periodic action. This reduces the time window for leakage current to affect the control voltage, thereby minimizing voltage ripple and jitter while maintaining control voltage stability through periodic updates.

The patent extracts the leakage current problem from the charge pump transistors by introducing separate leakage compensation paths. Instead of relying on expensive thick-oxide transistors to prevent leakage, the design uses standard transistors with additional compensation circuits that actively counteract the leakage current effects. This separates the main charge pump function from the leakage mitigation function, allowing standard transistors to be used while still achieving low leakage performance.

The patent makes the loop filter connection dynamic by controlling the switching of connection paths based on the phase detector output signals. Instead of a fixed continuous connection that would require large capacitors to filter ripple, the dynamic switching connects the loop filter to the charge pump output only when needed (during UP/DOWN signal phases). This dynamic approach reduces the effective time constant for ripple generation, allowing smaller capacitors to achieve the same voltage ripple reduction.