Dual-Path PLL Damping Control with Gated Integral Current

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Solution Overview

Problem

Traditional PLLs face challenges in achieving precise control over damping and bandwidth due to limitations in controlling gain in dual path loop filters, leading to issues with peaking and silicon area usage, especially in deep submicron technology applications where device mismatch and process variations are significant.

Innovation Solution

A dual path PLL with a gating circuit that digitally controls the integral charge pump current by sampling every p samples to provide an effective integral charge pump current, allowing for independent control of damping and bandwidth without increasing silicon area, and using a resistor and capacitor circuit to filter these currents for precise peaking control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a large value capacitor is used in the loop filter to achieve low bandwidth and low peaking specifications, then the peaking is reduced, but the silicon chip area is significantly increased

Engineering Contradiction:

ImprovepeakingVSAvoidsilicon chip area

Core Design Contradiction:

Object-affected harmful factorsVSArea of moving object

Solution Approach 1:

The loop filter is divided into two separate paths: a proportional path and an integral path. This segmentation allows independent control of bandwidth and peaking parameters, enabling low peaking without requiring a large capacitor in a single integrated filter circuit.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the control parameters by introducing separate gain controls for the proportional and integral paths. By independently adjusting these gains, the system can achieve low peaking specifications without being constrained by the capacitor value, thus reducing silicon area.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If the integral charge pump current is reduced to achieve precise damping control, then the peaking is improved, but the accuracy is limited by device mismatch and process variation

Engineering Contradiction:

ImprovepeakingVSAvoiddamping control accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The invention introduces dynamic control mechanisms including a gating circuit that selectively enables/disables the integral charge pump current, and a digital scaling circuit that dynamically adjusts the current magnitude. These dynamic elements provide precise control over the integral path gain, overcoming static limitations imposed by device mismatch and process variation.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention replaces analog current control mechanisms with digital control circuits. The digital scaling circuit uses binary-weighted current mirrors and switching networks to precisely control the integral charge pump current, providing higher accuracy and immunity to process variations compared to pure analog approaches.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If a dual path loop filter architecture is used to enable independent bandwidth and damping control, then the control flexibility is improved, but the device complexity increases

Engineering Contradiction:

Improvebandwidth and damping controlVSAvoidloop filter structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The proportional and integral charge pumps are designed to operate in a unified manner, with both paths sharing common control signals and scaling mechanisms. This multi-functional design allows the same basic circuit blocks to serve multiple purposes, reducing overall complexity despite the dual-path architecture.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The digital scaling circuits are nested within the existing dual-path loop filter structure. The scaling mechanisms are integrated into the charge pump stages themselves, with current mirrors and switching networks embedded within the proportional and integral paths, rather than adding separate external control circuits.

Inventive Principle:

Principle #7Nested doll (Nesting)

Data Source

PatentUS7777577B2Dual path phase locked loop (PLL) with digitally programmable damping

Publication Date: 2010.08.17 TEXAS INSTRUMENTS INC

AI summary

In a method and apparatus for controlling damping and bandwidth in a phase locked loop (PLL), a loop filter is configured to have a dual path for charge pump current. A 3 dB bandwidth of the PLL is controlled by adjusting gain of a proportional current path. An integral current path includes a gating circuit to digitally control an amount of time an integral charge pump current received is passed through as an effective integral charge pump current. A resistor and capacitor (RC) circuit filters the proportional and effective integral charge pump currents, thereby providing a filtered input to a voltage controlled oscillator. Damping and hence peaking of the PLL is precisely controlled by sampling one of every p samples of the integral charge pump current to provide the effective integral charge pump current, p being an integer.