Gilbert RF Mixer Current Injection for Low Noise and Linearity
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Solution Overview
Problem
Conventional RF mixers face a trade-off between noise figure and linearity, with decreased resistance and current reducing noise but increasing distortion, and increased resistance and current reducing distortion but increasing noise, necessitating a solution that improves both performance metrics.
Innovation Solution
The RF mixer incorporates a Gilbert mixer structure with an inputting stage, switching stage, and load stage, featuring CMOS transistors and additional current injection at the common source junctions of the switching stage, accompanied by inductors and capacitors to neutralize parasitic capacitance, thereby reducing second-order distortion and enhancing linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the current and resistance of the degeneration resistors are decreased, then the noise figure is improved, but the distortion increases
Solution Approach 1:
The switching stage is divided into two separate switch pairs instead of using a conventional single switch pair or degeneration resistors. Each switch pair operates independently with its own current source, allowing the circuit to achieve both low noise and low distortion by distributing the signal processing functions across multiple segmented components rather than relying on a single component with compromised parameters.
Solution Approach 2:
The invention changes the operational parameters of the switching stage by using two switch pairs with current sources that can be independently controlled. This allows optimization of both noise figure and distortion by adjusting the current distribution and switching characteristics, rather than being constrained by the fixed trade-off relationship in conventional single-switch-pair designs.
2Object-generated harmful factors
If the current and resistance of the degeneration resistors are increased, then the distortion is reduced, but the noise figure deteriorates
Solution Approach 1:
The switching stage is divided into two separate switch pairs instead of using a conventional single switch pair or degeneration resistors. Each switch pair operates independently with its own current source, allowing the circuit to achieve both low noise and low distortion by distributing the signal processing functions across multiple segmented components rather than relying on a single component with compromised parameters.
Solution Approach 2:
The invention changes the operational parameters of the switching stage by using two switch pairs with current sources that can be independently controlled. This allows optimization of both noise figure and distortion by adjusting the current distribution and switching characteristics, rather than being constrained by the fixed trade-off relationship in conventional single-switch-pair designs.
3Productivity
If a conventional Gilbert mixer structure is used, then the mixer achieves basic mixing function, but the linearity is degraded due to second-order distortion
Solution Approach 1:
The switching stage is divided into two separate switch pairs instead of using a conventional single switch pair or degeneration resistors. Each switch pair operates independently with its own current source, allowing the circuit to achieve both low noise and low distortion by distributing the signal processing functions across multiple segmented components rather than relying on a single component with compromised parameters.
Solution Approach 2:
The invention extracts and eliminates the source of second-order distortion by removing the conventional single switch pair configuration that generates even-order harmonics. By taking out the problematic single-switch-pair structure and replacing it with two independent switch pairs, the design eliminates the second-order distortion mechanism while preserving the essential mixing function.
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
This configuration significantly reduces second-order distortion, improving the mixer's linearity and noise figure, particularly beneficial for high-frequency applications by effectively canceling parasitic capacitance effects.
Implementation Method 1
The inductor neutralizes the effect of parasitic capacitance induced at the common source junction of each switch pair of the switching stage
Data Source
AI summary
A low noise RF mixer is described. The mixer of the present invention has excellent linearity due to reduction of second-order distortion. The mixer includes an inputting stage, a switching stage and a load stage. The inputting stage includes a switching pair and a transconductance circuit. The load stage is formed by resistors. The switching stage includes a switch quad (two switch pairs). Each switch pair of the switching stage has a current source for implementation of current injection to a common source (emitter) junction of the switch pair. For each switch pair of the switching stage, an inductor is connected between the current source and the common source (emitter) junction. In addition, a capacitor is connected with the inductor.