Multi-Path LNA Gain Control for Low Current and High Linearity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional low noise amplifiers (LNAs) face challenges in maintaining high linearity and noise figure while adjusting gain over a wide dynamic range, often resulting in impedance mismatch and distortion when reducing current to control gain, and attenuators fail to achieve desired power management and linearity.
Innovation Solution
A low noise amplifier architecture using multiple transistor paths with selectively shut-off FETs, configured as common source and cascode, and switches to maintain consistent impedance and linearity, allowing for adjustable gain modes including zero or negative gain, while reducing current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the gain of the LNA is reduced by controlling the bias of the common gate FET, then the current consumption is reduced, but the linearity of the LNA deteriorates
Solution Approach 1:
The LNA is divided into multiple parallel paths (first path with first common source FET and first common gate FET, second path with second common source FET and second common gate FET) that can be independently controlled. This segmentation allows selective activation of paths based on signal strength, enabling current reduction by deactivating paths rather than reducing bias on active FETs, thereby maintaining linearity in active paths.
Solution Approach 2:
The patent implements dynamic gain control by selectively enabling or disabling paths based on signal conditions. The bias control dynamically switches between different path configurations, allowing the system to adapt current consumption to signal strength while maintaining optimal linearity in the active path through proper bias management.
2Use of energy by moving object
If the current is reduced by controlling the bias to adjust gain, then the power consumption is reduced, but the impedance match at the input deteriorates
Solution Approach 1:
By segmenting the LNA into multiple independently controllable paths, the patent allows impedance matching to be maintained in the active path while other paths are deactivated. The input impedance is determined only by the active path, ensuring proper matching without the complications of multiple biased paths.
Solution Approach 2:
The patent introduces switching mechanisms as intermediaries between the bias control and the FETs. These switches act as mediators that can completely disable unused paths, preventing their impact on input impedance while still allowing bias control to optimize the active path for both power efficiency and impedance matching.
3Power
If an attenuator is used to control the gain of the LNA, then the gain can be reduced, but the linearity and noise figure performance deteriorate
Solution Approach 1:
Instead of using a single attenuator that degrades signal quality, the patent segments the amplification function into multiple parallel LNA paths. Each path provides clean amplification without attenuation-induced distortion, and gain control is achieved by selectively combining or disabling paths rather than attenuating the signal.
Solution Approach 2:
Rather than using attenuation to reduce gain (which degrades linearity), the patent inverts the approach by using selective path activation and deactivation. Gain control is achieved by controlling which amplification paths are active, effectively using addition/subtraction of gain rather than attenuation, thereby maintaining linearity and noise figure performance.
Data Source
AI summary
An LNA having a plurality of paths, each of which can be controlled independently to achieve a gain mode. Each path includes at least an input FET and an output FET coupled in series. A gate of the output FET is controlled to set the gain of the LNA. Signals to be amplified are applied to the gate of the input FET. Additional stacked FETs are provided in series between the input FET and the output FET.