US 2012/0235718 A1Published application

Adaptive bandwidth phase-locked loop

AssigneeFreescale Semiconductor, Inc.

InventorsKrishna THAKUR, Deependra K. JAIN, Vinod K. JAIN

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Abstract

A phase-locked loop (PLL) generates an oscillator signal based on an input reference signal. A voltage-to-current converter converts a control voltage to a first current. A current-controlled oscillator generates the oscillator signal based on the first current. A dual charge pump circuit generates first and second charge pump currents having a predetermined ratio, based on a second current generated by a current mirror circuit and an error (feedback) signal. An active loop filter generates the control voltage based on the first and second charge pump currents. The active loop filter includes an input capacitance that varies with a variation in the predetermined ratio of the charge pump currents. The active loop filter also includes a transconductance stage having a transconductance that varies based on a third current generated by a current mirror circuit. The PLL bandwidth is independent of PVT variations and dependent only on the frequency of the input reference signal. In addition, the size of the input capacitor is relatively small so that the circuit requires very little space.

Claims16

Dependent claims

A phase-locked loop (PLL), comprising:

a voltage-controlled oscillator (VCO), including:
a voltage-to-current converter for converting a control voltage to a first current;
and
a current-controlled oscillator, connected to the voltage-to-current converter, for generating an oscillator signal based on the first current;
a phase detector, connected to the VCO, for generating an error signal based on an input reference signal and a fraction of the oscillator signal;
a current mirror circuit, connected to the voltage-to-current converter, for generating a second current based on a fraction of the first current;
a dual charge pump circuit connected between the phase detector and the voltage-to-current converter, for receiving the error signal and the second current, and generating first and second charge pump currents according to a predetermined ratio;
and
an active loop filter connected to the dual charge pump circuit, the current mirror circuit and the voltage-to-current converter, wherein the active loop filter generates the control voltage based on the first and second charge pump currents, and wherein the active loop filter includes:
an input capacitance that varies with variation in the predetermined ratio of the first and second charge pump currents;
and
a transconductance stage having a transconductance that varies based on a third current generated by the current mirror circuit, wherein the transconductance stage includes one or more input transistors that operate in a sub-threshold region.

9 more elements

A system for generating an oscillator signal, the system comprising:

a voltage-to-current converter for converting a control voltage to a first current;
a current-controlled oscillator connected to the voltage-to-current converter for generating the oscillator signal based on the first current;
a phase detector, connected to the current-controlled oscillator, for generating an error signal based on an input reference signal and a fraction of the oscillator signal;
a current mirror circuit, connected to the voltage-to-current converter, that generates a second current based on a fraction of the first current;
a dual charge pump circuit connected between the phase detector and the voltage-to-current converter, for receiving the error signal and the second current, and generating first and second charge pump currents according to a predetermined ratio;
and
an active loop filter connected to the dual charge pump circuit, the current mirror circuit and the voltage-to-current converter, wherein the active loop filter generates the control voltage based on the first and second charge pump currents, and wherein the active loop filter includes:
an input capacitance that varies with variation in the predetermined ratio of the first and second charge pump currents;
and
a transconductance stage having a transconductance that varies based on a third current generated by the current mirror circuit, wherein the transconductance stage includes one or more input transistors that operate in a sub-threshold region.

7 more elements

Dependencies are inferred from the claim text.