Compensated Current Cell Topology for DAC Glitch Scaling

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Solution Overview

Problem

Current digital to analog converters (DACs) experience performance degradation due to switching transients or glitches, which are difficult to control and scale effectively, especially in high-bit resolution applications like 14-bit DACs, where binary weighted current sources are challenging to produce and scale.

Innovation Solution

A compensated current cell design is introduced, featuring compensation devices that generate currents to scale and reduce glitches, allowing for accurate scaling of switching transients and improved DAC performance by combining compensation currents with output currents to produce compensated output currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If binary weighted current sources are used to reduce the number of current sources, then device complexity is reduced, but manufacturing precision deteriorates due to difficult current matching requirements

Engineering Contradiction:

Improvenumber of current sourcesVSAvoidcurrent matching accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The current sources are divided into two groups: binary weighted current sources for the most significant bits and compensated current sources for the least significant bits. This segmentation allows each group to be optimized for its specific function, with the compensated sources providing precise matching for LSB conversions while the binary weighted sources handle MSB conversions with fewer components.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different current source configurations are applied to different bit positions based on their specific requirements. The least significant bit current sources use compensation circuitry to ensure precise current matching, while the most significant bit current sources use simple binary weighting. This local optimization resolves the contradiction by applying the appropriate design approach to each specific context.

Inventive Principle:

Principle #3Local quality

2Device complexity

If binary weighted current sources are used to reduce device complexity, then ease of manufacture improves, but the ability to scale glitches deteriorates

Engineering Contradiction:

Improvenumber of current sourcesVSAvoidglitch scaling capability

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The compensation circuitry in the LSB current sources includes controllable switches that dynamically adjust the glitch magnitude based on the conversion requirements. This dynamic control allows the system to adaptively scale glitches according to the specific digital code being converted, resolving the contradiction between simplified device structure and glitch scaling capability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The compensation circuitry monitors the switching transients and applies corrective actions to scale the glitches appropriately. By using feedback from the switching events, the system can dynamically adjust the glitch magnitude to match the required precision for each bit position, enabling glitch scaling without increasing overall device complexity.

Inventive Principle:

Principle #23Feedback

3Device complexity

If uncompensated current switching is used, then device complexity is reduced, but measurement precision deteriorates due to uncontrolled switching transients

Engineering Contradiction:

Improvecurrent cell structureVSAvoidconversion accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The compensation circuitry captures the harmful switching transients and transforms them into useful compensation signals. By recovering the glitch energy and applying it in a controlled manner, the system converts the harmful effect into a beneficial correction that improves measurement precision without significantly increasing device complexity.

Inventive Principle:

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

Solution Approach 2:

The compensation circuit acts as an intermediary between the simple current switching and the final measurement output. It mediates the harmful switching transients by filtering, scaling, and correcting them before they affect the measurement precision, thereby protecting the overall system accuracy while maintaining simple current cell structures.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS8558727B2Compensated current cell to scale switching glitches in digital to analog convertors

Publication Date: 2013.10.15 QUALCOMM INC

AI summary

Compensated current cell to scale switching glitches in digital to analog convertors. A compensated current cell is disclosed that includes first and second switching transistors configured to switch an input current between first and second outputs based on first and second input signals, respectively, a first compensation transistor connected to the first input signal to provide a first compensation current that is connected to the second output, and a second compensation transistor connected to the second input signal to provide a second compensation current that is connected to the first output, the first and second compensation transistors having source terminals that are connected together. In another aspect, switching glitches are scaled based on a size difference between the switching transistors and the compensation transistors.