Cascode Low-Noise Amplifier Bias Control for Higher Linearity
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Solution Overview
Problem
Low noise amplifiers face challenges in achieving high linearity and low power consumption while maintaining a low noise figure, as increasing bias current to improve linearity increases power consumption and existing solutions, such as those using envelope detectors, often result in increased noise figures.
Innovation Solution
A low noise amplifier design incorporating a cascode amplifier with a common source and common gate amplifier, an envelope detector to measure signal power, and an envelope amplifier to control the common gate amplifier, which sets the envelope path gain to zero the third-order coefficient, thereby improving linearity without increasing noise figure or power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bias current is increased to improve linearity, then linearity is improved, but power consumption is increased
Solution Approach 1:
The bias current is made dynamically adjustable rather than fixed. The amplifier transitions from a static biasing scheme to a dynamic one where the bias current adapts to signal conditions, allowing high linearity only when needed (large input signals) while consuming minimal power during normal operation (small input signals).
Solution Approach 2:
The bias current parameter is changed based on input signal conditions. The system monitors input signal level and adjusts the bias current parameter accordingly - increasing it for large signals to improve linearity and maintaining it low for small signals to save power, thus optimizing the trade-off between linearity and power consumption.
2Use of energy by moving object
If envelope detector is added to adjust bias current, then power consumption is reduced, but noise figure is increased
Solution Approach 1:
An intermediate amplifier stage is introduced between the envelope detector and the common gate amplifier. This intermediary component buffers the control signal from the envelope detector, preventing noise from propagating to the main signal path while still enabling bias current adjustment. The intermediary amplifier isolates the noise-generating envelope detector from the sensitive LNA input.
3Reliability
If bias current is increased to suppress single-tone desensitization and cross modulation interference, then linearity is improved, but battery lifespan is decreased
Solution Approach 1:
The bias current is adjusted periodically or dynamically based on signal conditions rather than being continuously high. The system activates high bias current only during periods when large interfering signals are detected, and maintains low bias current during normal operation, thus improving linearity when needed while extending battery lifespan through reduced average power consumption.
Data Source
AI summary
Embodiments of the present general inventive concept include a low noise amplifier and method with an improved linearity while reducing a noise disadvantage (e.g., increase). One embodiment of a low noise amplifier can include a first transistor to receive an input signal at a control terminal thereof, a second transistor having a first terminal coupled to a second terminal of the first transistor, an envelope detector to output a control signal corresponding to a characteristic of the input signal and an envelope amplifier to amplify the control signal to be applied to a control terminal of the second transistor.