Multi-Path LNA Gain Switching Without Linearity Loss
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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, as reducing current to control gain often leads to non-linear states and impedance mismatches, degrading receiver performance.
Innovation Solution
A low noise amplifier architecture using multiple transistor groupings with selectively shut-off FETs, configured as common source and common gate cascode, and switches to maintain consistent impedance and linearity, allowing for adjustable gain modes with reduced current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the current is reduced to control the gain of the LNA, then the gain is reduced, but the linearity deteriorates as the FET enters a non-linear state
Solution Approach 1:
The LNA is divided into multiple parallel paths (first path with first and second FETs, second path with third and fourth FETs) where each path can be independently controlled. This segmentation allows selective activation of specific FETs to achieve different gain levels while maintaining optimal operating conditions and linearity in the active devices.
Solution Approach 2:
The circuit employs dynamic control through switches (first switch, second switch, third switch, fourth switch) that can selectively connect or disconnect FETs and control nodes based on the desired gain level. This dynamic reconfiguration enables the LNA to adapt its structure in real-time, maintaining high linearity across varying gain settings by ensuring active FETs operate in their optimal linear region.
2Use of energy by moving object
If the bias of the common gate FET is controlled to reduce current, then the current consumption is reduced, but the impedance match at the input deteriorates
Solution Approach 1:
The input stage is segmented into parallel paths with independent FETs that can be selectively activated. When current consumption needs to be reduced, only necessary FETs remain active while others are switched off, maintaining proper impedance matching through the remaining active devices rather than relying on bias control that would degrade the match.
Solution Approach 2:
Switches are introduced as intermediary elements between the control logic and the FETs. These switches provide a clean on/off control mechanism that allows current consumption to be reduced by disabling entire paths rather than partially biasing FETs, thereby avoiding the impedance matching degradation that would result from bias control.
3Adaptability or versatility
If an amplifier with substantial gain is provided that can be reduced, then the dynamic range is extended, but the device complexity increases
Solution Approach 1:
Instead of using a single complex variable gain amplifier, the solution segments the amplification function into multiple parallel fixed-gain paths. Each path contains a specific number of FETs configured to provide a discrete gain level. This segmentation simplifies the overall architecture by replacing a complex continuously-variable amplifier with multiple simpler fixed-gain stages that can be selectively combined.
Solution Approach 2:
The system achieves dynamic range extension through dynamic selection of active paths rather than through a complex variable gain mechanism. Switches dynamically reconfigure which FETs and paths are active based on the required gain level, providing adaptability across a wide dynamic range while keeping each individual path relatively simple in structure.
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.