Gilbert Mixer DC Decoupling for Lower LO Feedthrough
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The Gilbert mixer in RF front-ends of wireless transceivers suffers from local oscillator (LO) feedthrough due to device mismatches between intermediate frequency transistors, which degrades system performance and requires complex additional filtering.
Innovation Solution
Incorporating DC decoupling components between switching and intermediate frequency transistors, along with large resistive components for biasing, to reduce the impact of mismatches and minimize LO feedthrough, allowing for improved performance without increasing circuit complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If DC coupling is used between switching transistors and intermediate frequency transistors, then circuit complexity is reduced, but LO feedthrough increases due to mismatches between intermediate frequency transistors
Solution Approach 1:
DC blocking capacitors are introduced as intermediary components between the switching transistors and intermediate frequency transistors. These capacitors block DC current while allowing AC signals to pass, thereby preventing DC coupling mismatches from causing LO feedthrough while maintaining circuit simplicity. The capacitors serve as mediators that isolate the DC operating points of different transistor stages.
Solution Approach 2:
The circuit is segmented into distinct DC isolated stages by inserting DC blocking capacitors. This segmentation separates the DC operating point control from the AC signal path, allowing each stage (switching transistors and intermediate frequency transistors) to be independently biased without requiring precise DC matching between stages, thus reducing LO feedthrough.
2Productivity
If DC current through intermediate frequency transistors is increased, then switching performance improves, but mismatches between transistors have greater impact on LO feedthrough
Solution Approach 1:
DC blocking capacitors act as intermediaries that allow high DC currents to flow through the intermediate frequency transistors for improved switching performance, while simultaneously blocking these DC currents from coupling to the switching transistor stage. This prevents the DC current mismatches from causing LO feedthrough, resolving the contradiction between performance and harmful effects.
3Reliability
If additional filtering is added to reduce LO feedthrough, then system performance improves, but device complexity increases
Solution Approach 1:
DC blocking capacitors are placed at the source to prevent LO feedthrough generation at its origin, rather than adding complex filtering stages to remove it later. This preliminary action blocks the DC coupling path that causes mismatches, thereby preventing LO feedthrough before it can degrade system performance, avoiding the need for additional complex filtering.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces LO feedthrough by decoupling DC currents, enhancing signal cancellation and allowing for simpler, more effective RF front-end designs that can be integrated into a single chip, with improved mean and standard deviation of LO feedthrough suppression.
Implementation Method 1
one or more DC decoupling components coupled between the switching transistors (Q3, Q4, Q5, Q6) and the intermediate frequency transistors (Q1, Q2) in order to DC decouple the switching transistors (Q3, Q4, Q5, Q6) from the intermediate frequency transistors (Q1, Q2)
Data Source
AI summary
A Gilbert mixer (200) comprising four switching transistors (Q3, Q4, Q5, Q6), two intermediate frequency transistors (Q1, Q2), and one or more DC decoupling components (202). The one or more DC decoupling components (202) are coupled between the switching transistors (Q3, Q4, Q5, Q6) and the intermediate frequency transistors (Q1, Q2) in order to DC decouple the switching transistors (Q3, Q4, Q5, Q6) from the intermediate frequency transistors (Q1, Q2).