RFDAC Unit-Cell Impedance Matching for High Linearity
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Solution Overview
Problem
Current radio frequency digital-to-analog converters (RFDACs) face challenges in maintaining consistent output impedance between active and sleep states, leading to impedance mismatch and signal-dependent charge injection, which degrades error vector magnitude (EVM) in high-order modulation transmissions.
Innovation Solution
The design of an improved RFDAC with dynamic impedance matching between active and sleep modes, achieved through a voltage-mode architecture where the output impedance of unit cells in sleep mode is set equal to that in active mode using a passive network, and a sleep switch configuration that eliminates common-mode charge injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If DAC unit cells are switched between active and sleep states to reduce power consumption, then power efficiency is improved, but output impedance mismatch occurs between states
Solution Approach 1:
A sleep switch is introduced as an intermediary component connected between the output of each DAC unit cell and ground. This switch acts as a mediator that maintains impedance continuity by providing a controlled path to ground in sleep mode, preventing impedance mismatch when unit cells are switched between active and sleep states.
Solution Approach 2:
The output impedance parameter of the DAC unit cell is dynamically adjusted by controlling the sleep switch. In sleep mode, the switch is activated to change the effective output impedance to match the active state impedance, while in active mode the switch is deactivated. This parameter change ensures consistent impedance characteristics across different operational states.
2Use of energy by moving object
If DAC unit cells are switched between active and sleep states to improve power efficiency, then power consumption is reduced, but signal-dependent charge injection occurs
Solution Approach 1:
The sleep switch serves as an intermediary that controls the discharge path of the unit cell capacitor. By providing a dedicated switch-controlled path to ground, it prevents unwanted charge injection into the signal path when unit cells transition between states, thereby eliminating signal-dependent charge injection errors.
Solution Approach 2:
The harmful charge injection effect is extracted and redirected through the sleep switch to ground, separating it from the main signal path. This extraction removes the harmful effect from the signal while maintaining the power-saving switching functionality.
3Reliability
If impedance matching is implemented between active and sleep modes to improve linearity, then error vector magnitude is reduced, but device complexity increases
Solution Approach 1:
The impedance matching solution is segmented and applied individually to each DAC unit cell through separate sleep switches. This modular approach allows impedance matching to be implemented at the unit cell level without requiring complex system-wide modifications, thereby limiting the increase in overall device complexity.
Solution Approach 2:
The output impedance parameter is dynamically adjusted using simple switch control rather than complex impedance matching networks. By changing the impedance state through a binary switch (on/off) rather than using complex reactive components, the solution achieves impedance matching with minimal additional circuit complexity.
Data Source
AI summary
Certain aspects of the present disclosure are directed to a radio frequency digital-to-analog converter (RFDAC). The RFDAC generally includes a plurality of digital-to-analog (DAC) unit cells. At least one DAC unit cell is capable of being configured in an active state or in a sleep state. For the at least one DAC unit cell, an output impedance of the DAC unit cell in the active state is equal to an output impedance of the DAC unit cell in the sleep state.