Current-Steered DAC with Data-Independent Common-Mode Dynamics
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional digital-to-analog converters (DACs) face challenges in achieving sufficient linearity due to common-mode signal dependencies, which are not proportional to differential currents, especially in noisy environments and high-speed operations, leading to limited common-mode rejection ratio (CMRR) and dynamic linearity issues.
Innovation Solution
The proposed electronic circuit for a DAC introduces an extra common-mode signal that is independent of the digital input signal, allowing for easier filtering by ensuring the common-mode contribution is predictable and signal-independent, achieved through the use of additional current sources and control signals that create a periodic and identical response in both differential outputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional DAC configuration with multiple current sources is used, then digital to analog conversion is achieved, but common-mode signal depends on digital input data causing linearity issues
Solution Approach 1:
The patent segments the common-mode signal into two independent parts: the original common-mode signal from the differential current sources and an additional common-mode signal from separate sources. This segmentation allows each part to be independently controlled and optimized, with the additional signal specifically designed to compensate for input-dependent variations.
Solution Approach 2:
The patent introduces an intermediary common-mode signal through additional current sources that acts as a mediator to counterbalance the harmful input-dependent common-mode variations. This intermediary signal serves as a correction mechanism that improves linearity without affecting the differential output signal.
2Object-affected harmful factors
If current-mode differential output is used, then noise rejection is improved, but common-mode signal contribution remains signal-dependent reducing CMRR
Solution Approach 1:
The patent implements a feedback mechanism where the additional common-mode signal sources are controlled to produce a signal that compensates for variations in the original common-mode signal. This feedback approach ensures that the total common-mode signal remains stable and independent of the digital input, thereby improving CMRR while maintaining noise rejection benefits.
3Productivity
If high-speed operation is implemented, then productivity is improved, but dynamic linearity issues arise due to common-mode signal variations
Solution Approach 1:
The patent applies preliminary action by pre-establishing the additional common-mode signal sources and their control circuitry before high-speed conversion operations begin. This preparation ensures that when high-speed operations occur, the common-mode compensation is already in place and can immediately counterbalance any input-dependent variations, maintaining dynamic linearity at high speeds.
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A current-steered DAC has first and second differential outputs for providing an analog output signal under control of a digital input signal. In operational use of the DAC, the output signal has a differential component, which is representative of the digital input signal, and also has a first common-mode component. The DAC has circuitry operative to add an extra common-mode component to both the first and second differential outputs so as to make a sum of the first common-mode component and the extra common-mode component substantially independent of a state change of the digital input signal.