Current-Steering DACs With Triode Switches for Low-Distortion Speed
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Solution Overview
Problem
Conventional current steering digital-to-analog converters face issues such as limited voltage headroom, high power usage, reduced speed due to large transistors, and data-dependent distortion, which affect their performance and predictability.
Innovation Solution
The solution involves using resistors instead of transistors to reduce voltage drops and RC constants, biasing current steering switches in the triode region to minimize output impedance, and incorporating reset switches to mitigate capacitance effects and data-dependent distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional current steering switches are used in saturation mode, then current steering capability is achieved, but voltage headroom is limited and power consumption increases
Solution Approach 1:
The patent changes the operating region parameter of the current steering switches from saturation mode to triode mode. This parameter change reduces the voltage drop across the switches, thereby improving voltage headroom and reducing power consumption while enabling high-speed operation beyond 10 GHz
2Power
If large transistors are used for current steering switches, then current handling capability is improved, but speed is reduced due to increased capacitance
Solution Approach 1:
The patent changes the operating region from saturation to triode, which fundamentally alters the capacitance characteristics of the switches. In triode mode, the reduced voltage swing and optimized operating point decrease the effective capacitance, enabling faster switching speeds while maintaining adequate current handling capability
3Reliability
If conventional DAC unit cells are used, then data conversion function is achieved, but data-dependent distortion occurs
Solution Approach 1:
The patent changes the operating region parameter to triode mode, which provides more linear resistance characteristics for the current steering switches. This parameter change reduces the non-linearity that causes data-dependent distortion, thereby improving conversion accuracy and reliability
Data Source
AI summary
Current steering digital-to-analog converters (DACs) are described. These DACs are suitable for high speed operation. Weight transistors conventionally used in DACs are replaced with resistors, resulting in a lower RC constant. Further, the resistors cause a smaller voltage drop, thus improving the voltage headroom of the DAC. Additionally, the current steering switches are biased in the triode region, as opposed to the saturation region as in conventional designs. Biasing the switches in the triode region results in a smaller drain-source voltage, which further improves the voltage headroom of the DAC. The triode operation further results in a substantially smaller output impedance, which leads to the output voltage being dictated primarily by the output transistor of the current path. Lastly, reset switches are added which reduce data-dependent memory effects that can otherwise produce distortion.