US 8,508,267 B1 · Loop filter for current-controlled-oscillator-based phase locked loop

Abstract

A loop filter of a phase-locked loop (PLL) that uses a current-controlled oscillator (CCO) includes a capacitor, a voltage-to-current (V-to-I) converter, and a charge pump. The input node of the loop filter receives a first current from an external charge pump. The combination of the capacitor and the V-to-I converter generates a first component of the output current of the loop filter based on the first current. The charge pump of the loop filter generates a second component of the output current. The loop filter is implemented without the need for a zero-frequency-determining resistor, the resistor instead being realized by the product of the first current, the second component of the output current and the transconductance of the V-to-I converter. Phase noise reduction in the PLL, as well as implementation of the loop filter with a smaller area, are thus made possible.

Claims11

Dependent claims

A loop filter of a phase-locked loop (PLL), the loop filter comprising:

a first capacitor coupled between an input node of the loop filter and a constant reference potential, the first capacitor to receive a first current generated by a first charge pump external to the loop filter, the first current generating a first voltage at the input node;
a voltage-to-current converter (V-to-I) circuit coupled to receive the first voltage and to generate a first component of an output current at an output node of the loop filter;
a second charge pump to generate a second component of the output current at the output node, wherein the output current is the sum of the first component and the second component.

A phase locked loop (PLL) comprising:

a phase detector to receive a reference clock and a feedback clock as inputs, and to generate an error signal proportional to a phase difference between the reference clock and the feedback clock;
a loop filter to generate an output current by low-pass filtering the error signal;
a current controlled oscillator (CCO) to generate an output clock with a frequency proportional to the output current;
and
a frequency divider to generate the feedback clock from the output clock,
wherein the loop filter comprises:
a first capacitor coupled between an input node of the loop filter and a first constant reference potential, the first capacitor to receive the error signal, the error signal generating a first voltage at the input node;
a voltage-to-current converter (V-to-I) circuit coupled to receive the first voltage and to generate a first component of the output current;
a first charge pump to generate a second component of the output current, wherein the output current is the sum of the first component and the second component, wherein the output current is provided at an output node of the loop filter.

6 more elements

Dependencies are inferred from the claim text.

Loop filter for current-controlled-oscillator-based phase locked loop

Life of this patent

Loop filter for current-controlled-oscillator-based phase locked loop

Life of this patent

Abstract

Claims11