On-chip loop filter for a PLL

摘要

An on-chip loop filter includes a 1^st resistor, a 1^st capacitor, a 2^nd capacitor, a 3^rd capacitor, a 2^nd resistor, and a 4^th capacitor. The 1^st resistor is operably coupled to receive a charge pump output. The 1^st capacitor is coupled in series with the 1^st resistor where the second node of the 1^st capacitor is coupled to a return. The 2^nd capacitor is coupled in parallel with the series combination of the 1^st resistor and 1^st capacitor. The 3^rd capacitor is coupled in parallel with the 2^nd capacitor. The 2^nd resistor is coupled to a node of the 3^rd capacitor and to a node of the 4^th capacitor. The other node of the 4^th capacitor is coupled to ground. To enable these components to be placed on-chip, the 1^st capacitor is of a 1^st capacitor construct having a 1^st quality factor, the 2^nd capacitor is of a 2^nd capacitor construct having a 2^nd quality factor, where the 2^nd quality factor is greater than the 1^st quality factor, and the 3^rd and 4^th capacitors are of a 3^rd capacitor construct having a 3^rd quality factor, which is greater than the 2^nd quality factor.