Complementary Current Steering Switches for DAC Settling Timing Errors
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Solution Overview
Problem
Current steering digital to analog converters face timing errors due to the inability to scale switches proportionally with decreasing current, leading to settling timing errors and reduced dynamic performance, especially in high-speed applications.
Innovation Solution
The use of complementary current steering switches, where two pairs of switches are cross-coupled and reversed in polarity to generate a smaller current, allowing for non-proportional scaling and reducing settling timing errors by using a normalized scaling factor of (p-1)/p, where p is a positive real number.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If switches are scaled down proportionally to the current being provided, then timing errors are reduced, but device sizes are limited by the production process and cannot be scaled indefinitely
Solution Approach 1:
The patent divides a single current steering switch into two complementary switches (first and second switches) that operate together. Each switch handles a portion of the current steering function, allowing the circuit to achieve better timing performance without requiring individual switches to be scaled below production process limits. The complementary operation of the two switches maintains overall timing accuracy.
Solution Approach 2:
The patent applies different scaling factors to different components within the current steering element. The switches are scaled according to a normalized scaling factor of (p-1)/p, while the current sources are scaled according to 1/p. This differential scaling allows each component to be optimized for its specific function while maintaining overall timing performance.
2Productivity
If higher sample rates are achieved in current steering DACs, then instantaneous bandwidth is improved, but settling timing errors increase and affect dynamic performance
Solution Approach 1:
The patent introduces dynamic scaling factors that can be adjusted based on operating conditions. The normalized scaling factor (p-1)/p allows the circuit to optimize its performance characteristics for high-speed operation, enabling the DAC to maintain timing accuracy even at elevated sample rates where settling errors would normally increase.
Solution Approach 2:
The patent changes the scaling parameters of the switches and current sources to optimize timing performance. By using a normalized scaling factor of (p-1)/p for switches and 1/p for current sources, the circuit achieves better settling behavior that maintains dynamic performance at high sample rates.
Data Source
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AI summary
The present disclosure provides embodiments of an improved current steering switching element for use in a digital to analog (DAC) converter. Typically, each current steering switching element in the DAC converter provides a varying set of currents for converting a digital input signal. Generally, the switches and drivers in the current steering switching elements are scaled down proportionally to the current being provided by the current steering switching element according to a ratio as less and less current is being driven by the switching element in order to overcome timing errors. However, device sizes are limited by the production process. When a switch is not scaled proportionally to the current, settling timing errors are present and affects the performance of the DAC. The improved current steering switching element alleviates this issue of timing errors by replacing the single switch with two complementary current steering switches.