I/Q Mixer Bias Control for Wireless Transmitter Linearity
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Solution Overview
Problem
Conventional wireless transmitters face challenges in achieving high linearity and compliance with stringent regulatory specifications for adjacent channel emissions and spectrum emission masks, particularly in supporting multi-user and MIMO operations.
Innovation Solution
The implementation of a wireless transmitter with a predistortion bias control circuit and current-sensing circuitry, which includes in-phase and quadrature DC level shifters, voltage-to-current converters, and mixers, allows for improved linearity and calibration of mixers, enabling efficient upconversion and gain control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional wireless transmitter designs are used, then device complexity is reduced, but linearity and compliance with regulatory specifications deteriorate
Solution Approach 1:
The patent implements a feedback mechanism where the bias control circuit continuously monitors the operating points of the I and Q signal paths and adjusts the bias voltages accordingly. This closed-loop control ensures that the mixer operates at optimal linearity points while automatically compensating for process variations and environmental changes, thereby achieving high linearity without requiring overly complex fixed biasing networks.
Solution Approach 2:
The patent dynamically adjusts the bias voltage parameters of the mixer based on the detected signal conditions. By changing the bias voltage levels in response to signal amplitude and phase variations, the system maintains optimal linearity across different operating conditions. This parameter adaptation allows the transmitter to achieve regulatory compliance without requiring multiple fixed biasing circuits for different operating modes.
2Object-generated harmful factors
If bias control circuits are added to improve linearity, then adjacent channel emissions are reduced, but device complexity increases
Solution Approach 1:
The patent combines the bias control functionality with the existing mixer structure by integrating the bias control circuit into the I and Q signal paths. Rather than adding completely separate control systems, the bias adjustment mechanisms are merged with the existing signal processing components, sharing common elements such as voltage references and control logic. This integration reduces the overall complexity increase while achieving the goal of reducing adjacent channel leakage.
3Manufacturing precision
If separate bias control for I and Q paths is implemented, then signal-to-noise ratio is improved, but manufacturing complexity increases
Solution Approach 1:
The patent employs a universal bias control architecture where a single bias control circuit is designed to manage both the I and Q signal paths. This multi-functional approach uses common voltage references, shared control logic, and interchangeable bias adjustment mechanisms that can be applied to either path. The modular design allows the same circuit block to be replicated or configured for different paths, simplifying the manufacturing process while maintaining separate bias control capabilities for optimal signal-to-noise ratio performance.
Data Source
AI summary
Certain aspects of the present disclosure generally relate to electronic circuits, and more particularly, to wireless transmitters. One example apparatus generally includes: an in-phase direct-current (DC) level shifter; a quadrature DC level shifter; an in-phase voltage-to-current (V2I) converter having an input coupled to an output of the in-phase DC level shifter; a quadrature V2I converter having an input coupled to an output of the quadrature V2I converter; a bias control circuit having inputs coupled to the in-phase V2I converter and the quadrature V2I converter, an output of the bias control circuit being coupled to at least one of the in-phase DC level shifter or the quadrature DC level shifter; an in-phase mixer having an input coupled to an output of the in-phase V2I converter; and a quadrature mixer having an input coupled to an output of the quadrature V2I converter.