Digital Transmitter Duty-Cycle Correction for Mixer Linearity
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Solution Overview
Problem
Switched capacitor transmitters and power amplifiers suffer from sensitivity to power supply impedance and clock overlap, leading to degradation in linearity, which existing technologies have not effectively addressed.
Innovation Solution
The system employs a duty cycle correction method involving coefficient calibration using a loopback circuit to measure and correct interference due to duty-cycle imperfections in the transmission path, reversing the order of Q bits, intelligently selecting a low-IF transmit path, and using quadrant-dependent LOFT cancellation to improve error vector magnitude and reduce out-of-band interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If switched capacitor transmitters and power amplifiers are used to achieve high power efficiency, then power consumption is reduced, but linearity degrades due to sensitivity to power supply impedance and clock overlap
Solution Approach 1:
The patent applies preliminary action by performing coefficient calibration before actual transmission. The system measures duty cycle errors using a loopback circuit and pre-compensates for these errors by adjusting coefficients, thereby eliminating the harmful effects of clock overlap and power supply impedance sensitivity before they degrade linearity during transmission.
Solution Approach 2:
The patent implements feedback through a loopback circuit that measures the actual duty cycle errors in the transmission path. This measured information is fed back to adjust the transmission coefficients, creating a closed-loop system that continuously compensates for non-linearities caused by the switched capacitor architecture, thus maintaining linearity while preserving power efficiency.
2Device complexity
If duty cycle errors are not corrected, then device complexity remains low, but linearity degrades and out-of-band interference increases
Solution Approach 1:
The patent introduces an intermediary element - a loopback circuit - that measures duty cycle errors without being part of the main transmission path. This intermediary measurement system enables precise detection of non-linearities while keeping the main transmission architecture simple, thus improving linearity without significantly increasing overall device complexity.
3Reliability
If all RF digital transmitter cells are activated to ensure signal coverage, then signal quality is maintained, but power consumption increases
Solution Approach 1:
The patent applies local quality by enabling selective activation of RF digital transmitter cells based on local signal requirements. By using duty cycle error measurement and coefficient calibration, the system can identify which specific cells need to be active to maintain signal quality in different spatial locations, thereby activating only the necessary cells and reducing overall power consumption while maintaining coverage.
Data Source
AI summary
Disclosed herein are related to systems and methods for correcting non-linearity due to duty cycle error. In one aspect, a system includes a mixer configured to up-convert transmission (Tx) data, a coefficient calibrator configured to select a target value of a coefficient based on a measurement of an interference signal due to non-linearity of the mixer, and an interference canceller coupled to the coefficient calibrator and the mixer. In some embodiments, the interference canceller is configured to generate compensated Tx data based on the Tx data and the selected target value of the coefficient and provide the compensated Tx data to the mixer. In some embodiments, the compensated Tx data corrects for the non-linearity of the mixer.