This PLL loop filter is used with current-output charge-pumps:
GND === .---. | .-| Z |-. --- | '---' | --- | | i_N | ___ | |\ | -->----o---|___|--o--|-\ | ___ | >-o--- -->----o---|___|--o--|+/ i_P | | |/ --- ,---. --- | Z | | '---' === | GND === GND
Z is an R and C in series, optionally paralleled with another C.
This circuit can be used with voltage-output phase detectors; but the single-ended input impedances are not equal:
GND === .---. | .-| Z |-. --- | '---' | --- | | ___ | ___ | |\ | VN --|___|---o---|___|--o--|-\ | ___ ___ | >-o-- VP --|___|---o---|___|--o--|+/ | | |/ --- ,---. --- | Z | | '---' === | GND === GND
This circuit seems to have better input balance over a wider frequency range and is simpler:
GND === .---. | .-| Z |-. --- | '---' | --- | | ___ | ___ | |\ | --|___|---o---|___|--o--|-\ | ___ ___ | >-o-- --|___|---o---|___|--o--|+/ | |+ |/ --- --- --- === 10uF | | === === GND GND
Is there a downside?
TIA