Gilbert Cell Up-Conversion Mixer Linearization With Source-Node Capacitance
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Solution Overview
Problem
Up-conversion mixers in transmitters face challenges with non-linearity, leading to unwanted frequency spurs and spectral regrowth due to the non-linear conversion of baseband signals, which degrades bit-error-rate in adjacent channels and is power-hungry, especially with large baseband input values and small LO signals.
Innovation Solution
An up-conversion mixer with an impedance element, such as a capacitor, coupled between the input amplification part and the multiplication part to a power supply line, suppresses high-frequency in-band signal components, improving linearity and reducing power consumption by addressing the non-linearity of the current generated by the amplification part.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional up-conversion mixer structures are used, then the mixer can perform frequency conversion, but non-linear conversion results in unwanted frequency spurs and spectral regrowth
Solution Approach 1:
The mixer is divided into two functionally independent stages: a baseband current generation stage and an RF frequency translation stage. This segmentation allows the baseband stage to focus on linear current generation while the RF stage handles frequency conversion, improving overall linearity and reducing unwanted mixing products.
Solution Approach 2:
A linear baseband current serves as an intermediary between the baseband input signal and the RF output. This current is generated linearly in the first stage and then used to modulate the RF carrier in the second stage, ensuring that the conversion process maintains linearity and minimizes spectral regrowth.
2Reliability
If baseband input signal amplitude is reduced to improve linearity, then unwanted mixing components are reduced, but RF output signal power is proportionally reduced
Solution Approach 1:
The invention skips the traditional approach of relying on large LO signals for switching action. Instead, it rushes through the baseband current generation stage with optimized linearization techniques, allowing the use of smaller baseband signals while maintaining good linearity and avoiding the need for high-power RF amplification.
3Reliability
If resistive degeneration is used to provide linear baseband current, then linearity is improved, but power consumption increases and harmonic components remain
Solution Approach 1:
The invention changes the operating parameters of the baseband transistors to optimize the trade-off between linearity and power consumption. By carefully selecting bias currents and transistor dimensions, the baseband stage achieves sufficient linearity without requiring excessive power dissipation, and harmonic components are minimized through proper parameter selection.
Data Source
AI summary
An up conversion mixer has a Gilbert cell arrangement including an input amplification part for producing an amplified signal coupled to a multiplication part, the multiplication part being arranged to multiply the amplified signal by a local oscillator signal and output a mixed signal, the mixer also having a capacitor coupled from a node between the input amplification part and the multiplication part, to a power supply line, for suppressing unwanted high frequency signal components of the output signal of the multiplication part. The linearity of such mixers can be improved considerably by this impedance on the source node of the switch transistors. This capacitance can be placed to either VSS or to VDD. Notably this improvement can be achieved with low power consumption since no additional power is needed for the increased performance.