Differential Clock Duty Cycle Correction With Hybrid Current Injection

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Solution Overview

Problem

Conventional duty cycle correction circuits face challenges with non-linear step transfer functions, sub-threshold operation, and increased parasitic capacitance, which affect the range and resolution of clock signals, leading to unpredictable duty cycle corrections.

Innovation Solution

A differential clock duty cycle correction circuit with a hybrid current injector and tapered current digital-to-analog converter (DAC) is introduced, where the hybrid current injector is controlled by a portion of the DAC code to generate correction currents, and the tapered current DAC provides a constant reference current, preventing sub-threshold operation and ensuring linear step transfer functions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional duty cycle correction circuits are used, then duty cycle correction is provided, but non-linear step transfer functions occur leading to unpredictable corrections

Engineering Contradiction:

Improvepredictability of duty cycle correctionVSAvoidlinearity of step transfer function

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent changes the operational parameters of the current sources by preventing sub-threshold operation through proper biasing. The current sources are designed to operate in the saturation region with adequate overdrive voltages, which linearizes the relationship between control voltages and output currents, thereby achieving a linear step transfer function and predictable duty cycle corrections.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the conventional analog control mechanism with a hybrid approach that uses digital-to-analog converters (DACs) to generate precise control voltages. This substitution of control methodology eliminates the non-linearities associated with direct analog control and provides a linear, predictable step transfer function through digital precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Manufacturing precision

If conventional current sources are used in duty cycle correction circuits, then correction is provided, but sub-threshold operation occurs causing non-linearity

Engineering Contradiction:

Improvelinearity of current generationVSAvoidoperational stability

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent fundamentally changes the operational parameters of the current sources by ensuring they operate above the sub-threshold region. Adequate biasing voltages are applied to keep the transistors in the saturation region, where the current-voltage relationship is linear and predictable. This parameter change eliminates sub-threshold non-linearity while maintaining operational stability.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If duty cycle correction circuits are implemented, then clock signal correction is achieved, but parasitic capacitance increases reducing performance

Engineering Contradiction:

Improvecorrection accuracyVSAvoidparasitic capacitance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent employs minimalistic circuit topologies with thin-film transistor implementations that reduce parasitic capacitances. The hybrid current injector architecture uses efficient current mirroring and switching mechanisms that minimize the capacitance at critical nodes, thereby reducing the harmful parasitic effects while maintaining correction accuracy.

Inventive Principle:

Principle #30Flexible shells and thin films

4Manufacturing precision

If conventional DAC control is used, then duty cycle adjustment is provided, but non-constant reference current causes non-linearity

Engineering Contradiction:

Improvelinearity of DAC controlVSAvoidDAC circuit design

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent introduces an intermediary constant current source that mediates between the DAC control signals and the hybrid current injector. This constant reference current acts as a stable intermediary that ensures linear relationship between DAC codes and output current, eliminating the non-linearity caused by varying reference currents while adding minimal circuit complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS10784846B1Differential clock duty cycle correction with hybrid current injectors and tapered digital to analog converter

Publication Date: 2020.09.22 GLOBALFOUNDRIES US INC

AI summary

Embodiments of the disclosure provide a differential clock duty cycle correction (DCC) circuit, including: a hybrid current injector including current sources for generating a correction current, wherein the correction current is added to a clock signal of a first polarity at a first correction node and subtracted from a clock signal of an opposite polarity at a second correction node, and wherein a plurality of the current sources in the hybrid current injector are controlled by a first portion of a n-bit DAC code to generate the correction current; and a current DAC for receiving a second, different portion of the n-bit DAC code and for outputting a corresponding reference current to the current sources in the hybrid current injector, wherein the current sources generate the correction current in response to the reference current output by the current DAC for the second portion of the n-bit DAC code.