RF Mixer Biasing for Independent IP2 Calibration
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Solution Overview
Problem
Existing RF mixers face challenges in achieving optimal performance and second-order non-linearity, particularly in millimeter wave wireless applications, due to limitations in second-order intercept point (IP2) calibration, which affects intermodulation distortion.
Innovation Solution
The RF circuit incorporates a mixer with dual-gated transistors, utilizing separate front and back gate bias voltages, allowing independent IP2 calibration decoupled from gate biasing, and includes a front gate bias voltage generator and a back gate bias voltage generator with a digital-to-analog converter to adjust second-order non-linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single gate bias voltage is used for mixer transistors, then the circuit complexity is reduced, but the second-order non-linearity performance deteriorates
Solution Approach 1:
The gate bias voltage is segmented into two independent components: front gate bias voltage and back gate bias voltage. This segmentation allows separate control of transistor threshold voltage and channel characteristics, enabling independent optimization of mixer performance and second-order non-linearity without increasing overall circuit complexity
Solution Approach 2:
The invention changes the electrical parameters by introducing programmable bias voltages that can dynamically adjust the transistor operating point. The front gate bias voltage controls the primary switching operation while the back gate bias voltage independently adjusts the second-order non-linearity characteristics, allowing real-time parameter optimization
2Manufacturing precision
If gate bias voltage is used for IP2 calibration, then second-order non-linearity is improved, but the independence from performance optimization is lost
Solution Approach 1:
The bias control is segmented into two independent voltage sources: front gate bias voltage for performance optimization and back gate bias voltage for IP2 calibration. This segmentation completely decouples the two functions, allowing independent adjustment of mixer performance and second-order non-linearity without interference
Solution Approach 2:
The back gate bias voltage acts as an intermediary mechanism that specifically targets the second-order non-linearity without affecting the primary mixing function. By introducing this intermediate control element, the system achieves independent IP2 calibration while maintaining optimal performance through separate front gate control
3Object-generated harmful factors
If traditional IP2 calibration is performed, then second-order intermodulation distortion is reduced, but chip area increases due to additional decoupling capacitors
Solution Approach 1:
The invention replaces the traditional capacitive decoupling approach with an active voltage control mechanism. Instead of using large decoupling capacitors to achieve IP2 calibration, the system uses programmable back gate bias voltages to actively control and cancel second-order non-linearity, significantly reducing the required chip area while maintaining distortion reduction performance
Data Source
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AI summary
Disclosed is a radio frequency (RF) circuit including a mixer configured for independent second order intercept point (IP2) calibration. The mixer includes three ports and multiple dual-gate transistors interconnected therebetween for down-converting an RF input signal to a lower frequency baseband output signal. To optimize performance, front gates of the transistors are biased with a front gate bias voltage (Vfg). To adjust second order non-linearity, back gates of the transistors are biased using a first back gate bias voltage (Vbgp) for half of the transistors of the mixer and a second back gate bias voltage (Vbgm) for a different half of the transistors. The circuit can also include a front gate bias voltage generator for generating Vfg and a back gate bias voltage generator (including a digital-to-analog converter (DAC) with multiple DAC units) for generating Vbgp and Vbgm independent of Vfg. Also disclosed is an associated operating method.