Patent ID: 6766154
Filing Date: 2004-07-20
Classification: H03L

Abstract:
An active loop filter for a phase locked loop, said active loop filter having an input for receiving a phase error signal, an output for supplying a control voltage, and being switchable in bandwidth characteristic between a narrow bandwidth and a broader bandwidth, comprising at least:an amplifier, said amplifier having an inverting input, a non-inverting input and an output; a first resistor and a capacitor, said first resistor and capacitor being connected in electrical series circuit between said inverting input and said output of said amplifier; a second resistor coupled between said inverting input of said amplifier and electrical ground, said second resistor providing a first predetermined resistance value to ground at said inverting input that enables a narrow bandwidth characteristic to said loop filter; electronic switch means, said electronic switch means having alternate conductive states, including a first state in which said electronic switch means is non-conducting and a second state in which said electronic switch means conducts fully, and a control input for controlling the conductive state in which said electronic switch means is disposed; and a third resistor, said third resistor being connected in electrical series with said electronic switch between said inverting input of said amplifier and electrical ground in shunt relationship to said second resistor, whereby operation of said electronic switch means to said second state provides a second predetermined resistance value to ground at said inverting input that enables a broader bandwidth characteristic to said loop filter; said non-inverting input of said amplifier for receiving said phase error signal from said input.