Charge Pump Current Regulation for PLL Spur Reduction

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Solution Overview

Problem

Prior art charge pump circuits face issues due to mismatches between current sources and sinks, which are load-dependent and result in degradation of PLL performance, particularly causing spurious frequency components, and existing solutions compromise output voltage range to achieve matching.

Innovation Solution

A self-regulated charge pump circuit where the current sink is adjusted based on the voltage of a filter circuit's second node, using a voltage-controlled current sink and feedback mechanism to ensure the output voltage tracks the filter circuit's voltage, allowing the current sink to match the current source without sacrificing output voltage range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If large transistors are used to guarantee good matching between current source and sink, then matching accuracy is improved, but circuit area increases

Engineering Contradiction:

Improvematching accuracyVSAvoidcircuit area

Core Design Contradiction:

Manufacturing precisionVSArea of stationary object

Solution Approach 1:

The patent introduces a feedback mechanism where the output voltage is sensed and fed back to adjust the current sink dynamically. This closed-loop feedback system automatically compensates for mismatches between current source and sink without requiring oversized transistors, thereby achieving good matching accuracy while maintaining compact circuit area

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent dynamically adjusts the current sink parameter based on the output voltage level. By changing the current sink value in response to voltage variations, the system maintains accurate matching across different operating conditions without relying on fixed large transistor dimensions

Inventive Principle:

Principle #35Parameter changes

2Reliability

If cascode topology is used to achieve high output resistance, then output resistance is improved, but output voltage range is reduced

Engineering Contradiction:

Improveoutput resistanceVSAvoidoutput voltage range

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent employs dynamic adjustment of the current sink based on the output voltage level. Instead of using a static cascode structure, the system continuously adapts the current sink value to maintain high effective output resistance while allowing the output voltage to swing over a wide range without being constrained by fixed topology limitations

Inventive Principle:

Principle #15Dynamics

3Reliability

If current source and sink are designed with high output impedance, then load independence is improved, but circuit complexity increases

Engineering Contradiction:

Improveload independenceVSAvoidcircuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent uses a feedback loop that senses the output voltage and adjusts the current sink accordingly. This feedback mechanism effectively decouples the current output from load variations, achieving load independence without requiring complex high-impedance circuit topologies. The feedback control simplifies the overall design compared to traditional high-impedance approaches

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS7492197B2Charge pump circuit with regulated current output

Publication Date: 2009.02.17 SIEMENS AG

AI summary

The output current of a current sink is regulated by a reference current provided by a current source and a reference voltage obtained by filtering the output voltage of the current sink. The current sink to be regulated is a voltage control current source, where the control voltage is obtained by amplifying the difference between the reference voltage and the output voltage of the current source.