Series-Connected Resistive Mixer for Higher IIP3 Linearity
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Solution Overview
Problem
Achieving a highly linear mixer with a large third-order input intercept point (IIP3) while minimizing conversion loss is challenging due to the trade-off between these two parameters in conventional mixer designs, which often result in undesirable intermodulation distortion and limited IIP3 performance.
Innovation Solution
A mixer design utilizing a plurality of active devices arranged in series, with different gate widths and sizes, to form unit cells that suppress non-linear third harmonics, where the active devices are connected in a series configuration with specific size ratios and biasing schemes to optimize IIP3 and conversion loss, including a common DC gate bias and 180-degree out-of-phase local oscillator signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional mixer designs use non-linear devices for frequency mixing, then the desired frequency shifting is achieved, but intermodulation distortion increases and IIP3 performance is limited
Solution Approach 1:
The mixer is divided into multiple unit cells, each containing series-connected active devices. This segmentation allows the overall mixer to achieve better linearity by distributing the mixing function across multiple smaller non-linear elements, reducing the intermodulation distortion generated by any single device while maintaining the required IIP3 performance.
Solution Approach 2:
Different active devices within each unit cell are designed with different gate widths to create local variations in non-linearity characteristics. This local quality differentiation enables each device to contribute differently to the mixing process, with larger devices providing stronger mixing action and smaller devices contributing to linearity, thereby reducing overall intermodulation distortion while maintaining conversion gain.
2Reliability
If the mixer is designed to be highly linear to maximize IIP3, then third order distortion products are reduced, but conversion loss increases
Solution Approach 1:
The mixer exploits the dynamic non-linear behavior of active devices by operating them in a regime where they exhibit sufficient non-linearity for effective mixing while maintaining acceptable linearity. The series connection of devices with different gate widths creates a dynamic response that optimizes the trade-off between conversion loss and IIP3 across the operating signal range.
Solution Approach 2:
The mixer uses a composite structure of active devices with different characteristics (different gate widths) connected in series. This composite approach combines the strengths of individual devices - larger devices provide conversion gain while smaller devices contribute to linearity - achieving a balance between conversion loss and IIP3 that neither device type could achieve alone.
3Loss of energy
If selective drain bias is applied to optimize conversion loss and IIP3, then some performance improvement is achieved, but the layout complexity increases
Solution Approach 1:
Multiple active devices with different gate widths are merged in series within each unit cell, sharing common biasing and control structures. This merging approach achieves performance optimization through device diversity while maintaining layout simplicity by using shared bias networks and common gate control, avoiding the need for complex independent biasing circuits for each device.
Data Source
AI summary
A unit cell for a resistive mixer includes a plurality of active devices arranged in series, wherein each of said plurality of active devices having a different output conductance. A resistive mixer includes a plurality of active devices connected in series with one another to form a unit cell.