Current-Steering DAC Common-Mode Current Removal Under PVT Variation
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Solution Overview
Problem
Existing digital-to-analog converters (DACs) face challenges in maintaining low common-mode current variation with changes in process, voltage, and temperature (PVT) without impacting digital signal performance and increasing noise, offset, area, or power consumption.
Innovation Solution
A DAC circuit with a plurality of current-steering cells and a resistor ladder circuit, featuring a first current sink coupled to the shunt branch and a second current sink coupled to the output, designed to remove common-mode current, with the second sink counteracting PVT variations by adjusting its current sinking based on resistance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If common-mode current removal is implemented in a DAC circuit, then common-mode current variation is reduced, but device complexity and power consumption increase
Solution Approach 1:
The common-mode current removal function is segmented into two separate current sinks: a first current sink connected to the shunt branch of the resistor ladder circuit, and a second current sink connected to the DAC output. This segmentation allows each sink to handle a portion of the common-mode current, reducing the complexity burden on any single component while achieving effective common-mode current suppression.
Solution Approach 2:
The patent introduces an intermediary mechanism where the second current sink acts as a compensating element that counteracts PVT variations affecting the first current sink. This intermediary current sink adjusts its current sinking dynamically to maintain overall common-mode current stability, effectively mediating between the varying parameters and the stability requirement.
2Measurement precision
If common-mode current removal circuitry is added, then noise and offset are reduced, but area and power consumption increase
Solution Approach 1:
The patent merges the common-mode current removal function with the existing DAC output structure by integrating the current sinks into the conventional current-steering cell and resistor ladder circuit architecture. This merging approach allows the common-mode current removal functionality to be achieved without adding significant external circuitry, thereby minimizing the increase in circuit area while still reducing noise and offset.
3Reliability
If current sinks are used to remove common-mode current, then common-mode current variation decreases, but power consumption increases
Solution Approach 1:
The patent applies partial action by designing the current sinks to handle only the common-mode current component rather than the full signal current. The first current sink processes a portion of the common-mode current from the shunt branch, while the second current sink handles the remaining portion from the output, achieving effective common-mode suppression with reduced power consumption compared to processing the entire current.
Data Source
AI summary
Methods and apparatus for common-mode current removal in a digital-to-analog converter (DAC). An example DAC circuit generally includes a plurality of current-steering cells, a resistor ladder circuit coupled to the plurality of current-steering cells, a first current sink coupled between a shunt branch of the resistor ladder circuit and a reference potential node for the DAC circuit, and a second current sink coupled between a first output of the DAC circuit and the reference potential node.