McGuireWoods LLP
Charge pump circuit for phase locked loop free from spike current
 A phase locked loop has a charge pump circuit connected through a loop filter to a voltage controlled oscillator, and the charge pump circuit is controlled by a frequency/phase comparator, wherein the charge pump circuit includes a first current mirror circuit responsive to a first control signal for regulating a discharging current from the loop filter to a first target amount proportional to a constant current, a second current mirror circuit for regulating a reference current to a second target amount proportional to the constant current and a third current mirror circuit responsive to a second control signal for regulating a charging current to the loop filter to a third target amount proportional to the reference current, a first switching circuit for charging a first parasitic capacitor coupled to the first current mirror circuit from the constant current source and a second switching circuit for charging a second parasitic capacitor coupled to the third current mirror circuit through the second current mirror circuit, thereby setting a limit on a spike current generated at a change of the first and second control signals. 
NEC Corporation
G H H
G11B H03L H03L
inventional inventional additional
Masaki
Sano