Current-Steering DAC Nonlinear Capacitance Compensation Circuit

Solution Overview

Problem

High signal frequencies in current steering DACs suffer from performance degradation due to non-linear parasitic capacitance, leading to reduced spurious free dynamic range (SFDR) and increased third-order intermodulation distortion (IM3).

Innovation Solution

Incorporating compensation transistors with varying sizes and bias voltages to counteract the non-linearity of cascode transistors, specifically designed to reduce the non-linear capacitive effects associated with gate-drain parasitic capacitance, thereby improving overall linearity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If current steering DACs operate at high signal frequencies, then productivity increases, but manufacturing precision deteriorates due to non-linear parasitic capacitance

Engineering Contradiction:

Improvesignal frequencyVSAvoidconversion linearity

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent introduces compensation capacitors that exploit the non-linear capacitance effect to counteract the harmful non-linearity of parasitic capacitance. By deliberately adding non-linear capacitive elements with opposite characteristics, the system converts the harmful non-linear effect into a beneficial compensation mechanism, thereby improving conversion linearity while maintaining high signal frequency operation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent modifies the capacitive parameters of the DAC circuit by adding compensation capacitors with specific non-linear characteristics. These capacitors are designed to have voltage-dependent capacitance values that change in opposition to the parasitic capacitance variations, thereby adjusting the overall capacitive behavior to achieve better linearity across the operating range

Inventive Principle:

Principle #35Parameter changes

2Reliability

If cascode transistors are used in DAC cells, then reliability improves through shielding, but object-generated harmful factors increase due to non-linear gate-drain parasitic capacitance

Engineering Contradiction:

Improveoutput shieldingVSAvoidparasitic capacitance non-linearity

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces compensation capacitors that exploit the non-linear capacitance effect to counteract the harmful non-linearity of parasitic capacitance. By deliberately adding non-linear capacitive elements with opposite characteristics, the system converts the harmful non-linear effect into a beneficial compensation mechanism, thereby improving conversion linearity while maintaining high signal frequency operation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The compensation capacitors act as intermediary elements between the cascode transistor and the output. These capacitors mediate the capacitive interaction by providing an additional non-linear capacitive path that counterbalances the parasitic capacitance, thereby reducing its harmful impact on signal linearity

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12184296B2Systems and method of compensating for nonlinear capacitance in converters

Publication Date: 2024.12.31 AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE LTD

AI summary

Described herein are systems and methods related to a converter includes a number of unit cells. The unit cells each include a first transistor and a second transistor. The first transistor is coupled in series with an output of the unit cell, and the second transistor is configured to have a capacitive characteristic that reduces a non-linear capacitive characteristic of the first transistor. The converter can be a voltage or current mode digital to analog converter.