Charge Pump Offset Cancellation Using Replica Feedback

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Solution Overview

Problem

Charge pumps in phase compare applications experience transient mismatches due to timing delays, leading to non-zero average current output even when signals have no phase difference, which worsens at higher frequencies, causing noise and offset control loop errors.

Innovation Solution

Coupling a primary charge pump with a replica charge pump and using a difference amplifier to measure and cancel error currents, ensuring equal but opposite currents are produced to maintain constant output voltage, and employing feedback to match transient outputs in a locked state.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If charge pump frequency is increased to improve productivity, then output current response speed is improved, but transient timing mismatches worsen causing non-zero average current error

Engineering Contradiction:

Improvecharge pump output current response speedVSAvoidaverage current accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where the charge pump output is fed back to dynamically adjust the timing of pump switches. This closed-loop feedback equalizes the enable/disable timing of positive and negative output currents, canceling transient mismatches and maintaining zero average current even at high frequencies where timing errors would normally accumulate.

Inventive Principle:

Principle #23Feedback

2Loss of time

If charge pump switching speed is increased to improve response time, then productivity is improved, but transient timing mismatches increase causing control loop errors

Engineering Contradiction:

Improvecharge pump response timeVSAvoidcontrol loop accuracy

Core Design Contradiction:

Loss of timeVSReliability

Solution Approach 1:

The patent makes the charge pump timing dynamic by using feedback from the output to continuously adjust switch enable/disable times. This dynamic timing adjustment ensures that even as switching speeds increase to reduce response time, the timing mismatches are automatically corrected, maintaining control loop reliability at high frequencies.

Inventive Principle:

Principle #15Dynamics

3Ease of manufacture

If ideal charge pump topology is used to simplify design, then ease of manufacture is improved, but transient timing mismatches cannot be eliminated

Engineering Contradiction:

Improvecharge pump design simplicityVSAvoidtransient error cancellation

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent maintains the simplicity of standard charge pump topologies while adding a feedback path that automatically corrects transient timing mismatches. This feedback approach eliminates the need for complex mismatch-cancellation circuits, preserving ease of manufacture while achieving high precision in transient error cancellation.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS8542043B2High speed DLL offset cancellation

Publication Date: 2013.09.24 ANALOG DEVICES INC

AI summary

In an embodiment, a primary charge pump and replica charge pump may be coupled to matching control mechanisms and loads. In an embodiment, the replica charge pump may produce an error current originating from charge pump timing mismatches in a steady locked loop state. The error current produced by the replica charge pump may be measured by a difference amplifier to adjust at least one current source to compensate for the error current originating from the timing mismatches. To adjust the current sources, the amplifier may cause the current source to produce an equal but opposite current to cancel the effects of the error current, resulting in a constant output voltage.