Switched-Capacitor PLL Loop Filter for Low Noise and Power

Solution Overview

Problem

Active switched-capacitor loop filters in phase-locked loops (PLLs) face issues with noise and high power consumption due to active elements, which affect area efficiency and performance in integrated circuits.

Innovation Solution

A loop filter design incorporating a first and second proportional capacitor, an active device, and switches that alternately couple these capacitors to a charge pump and into a feedback circuit, effectively reducing noise and power consumption by using a switched-capacitor architecture with an inverter and sub-threshold biasing to manage flicker noise and power usage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If an active switched-capacitor loop filter is used, then area efficiency is improved, but noise and power consumption increase

Engineering Contradiction:

Improvechip areaVSAvoidnoise

Core Design Contradiction:

Area of stationary objectVSObject-generated harmful factors

Solution Approach 1:

The loop filter is divided into two identical half-cycles, each containing proportional and integral components. The circuit operates in alternating phases where one half-cycle is active while the other is reset, allowing noise from active elements to be confined to individual phases and filtered out in the combined output.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The loop filter uses periodic switching between two half-cycles, with each cycle comprising a proportional phase and an integral phase. This periodic operation allows the circuit to achieve low noise performance by resetting active devices between cycles, preventing noise accumulation while maintaining area efficiency.

Inventive Principle:

Principle #19Periodic action

2Area of stationary object

If an active switched-capacitor loop filter is used, then area efficiency is improved, but power consumption increases

Engineering Contradiction:

Improvechip areaVSAvoidpower consumption

Core Design Contradiction:

Area of stationary objectVSUse of energy by stationary object

Solution Approach 1:

The loop filter is divided into two identical half-cycles, each containing proportional and integral components. The circuit operates in alternating phases where one half-cycle is active while the other is reset, allowing noise from active elements to be confined to individual phases and filtered out in the combined output.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The loop filter uses periodic switching between two half-cycles, with each cycle comprising a proportional phase and an integral phase. This periodic operation allows the circuit to achieve low noise performance by resetting active devices between cycles, preventing noise accumulation while maintaining area efficiency.

Inventive Principle:

Principle #19Periodic action

3Object-generated harmful factors

If an RC loop filter is used, then noise is reduced, but chip area increases

Engineering Contradiction:

ImprovenoiseVSAvoidchip area

Core Design Contradiction:

Object-generated harmful factorsVSArea of stationary object

Solution Approach 1:

The patent replaces the passive RC loop filter with an active switched-capacitor loop filter that uses switches and capacitors to simulate resistor functionality. This substitution eliminates the need for large physical resistors and capacitors, significantly reducing chip area while maintaining noise performance through periodic resetting of active elements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operating parameters of the loop filter by using switched-capacitor technology with periodic resetting. By operating active devices in alternating phases and resetting them periodically, the circuit achieves low noise characteristics similar to RC filters but with much smaller area requirements.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS9024684B2Area-efficient PLL with a low-noise low-power loop filter

Publication Date: 2015.05.05 QUALCOMM INC

AI summary

Techniques for reducing noise and power consumption in a loop filter for a phase-locked loop (PLL) are described herein. In one embodiment, a loop filter for a PLL comprises a first proportional capacitor, a second proportional capacitor, an active device, and a plurality of switches. The plurality of switches are configured to alternately couple the first proportional capacitor and the second proportional capacitor to a first charge pump, to alternately couple noise from the active device to the first proportional capacitor and the second proportional capacitor, and to alternately couple the first proportional capacitor and the second proportional capacitor into a feedback circuit, wherein the feedback circuit produces an output voltage of the loop filter.