Segmented Transistor Cell for Mixer Linearity Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Transistor parasitics vary significantly with applied gate voltage, impacting the linearity of transistor circuits, particularly in frequency mixers, where existing solutions fail to maintain high linearity and third-order intercept points.
Innovation Solution
A transistor cell comprising a parallel connection of transistors with voltage shifting resistors or engineered threshold voltages, allowing each transistor to turn on at different voltages, thereby reducing parasitic variation and enhancing linearity, specifically increasing the third-order intercept point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single transistor is used in a frequency mixer, then the circuit is simple, but the linearity and third-order intercept point are degraded due to significant parasitic variation with gate voltage
Solution Approach 1:
The single transistor is segmented into multiple transistors (first transistor and second transistor) with different threshold voltages. Each transistor handles a different portion of the input signal range, and their combined operation maintains consistent parasitic characteristics across the full signal range, thereby improving linearity and third-order intercept point.
Solution Approach 2:
Different transistors are designed with different threshold voltages to create local optimizations. The first transistor with a first threshold voltage handles specific signal portions while the second transistor with a second threshold voltage handles other portions, allowing each transistor to operate in its optimal region and maintain consistent parasitic behavior locally.
2Reliability
If multiple transistors with different threshold voltages are used, then parasitic variation is reduced and linearity is improved, but the device complexity increases
Solution Approach 1:
Multiple transistors with different threshold voltages are merged into a single transistor cell structure. The transistors are coupled together such that their combined drain currents provide the total output current, while their gate terminals are connected to the same control signal. This merging allows the complex functionality of multiple transistors to be achieved within a unified cell structure.
Solution Approach 2:
The threshold voltage parameter is deliberately changed across different transistors in the cell. By selecting transistors with different threshold voltages, the invention creates a set of transistors that turn on at different gate voltages, allowing them to collectively cover a wider range of input signals while maintaining consistent parasitic characteristics throughout the operating range.
Data Source
AI summary
A transistor cell is provided that includes transistors arranged to turn on for different voltages applied to a control terminal of the transistor cell. The transistor cell can include a first transistor having a gate, a source, and a drain, and a second transistor having a gate, a source, and a drain, wherein the source of the second transistor is coupled to the source of the first transistor, and the drain of the second transistor is coupled to the drain of the first transistor. The transistor cell can further include a first resistor coupled between the gate of the first transistor and the gate of the second transistor. A frequency mixer is also provided that includes at least one transistor cell.