Cascode Low Noise Amplifier Gain Control Without Separate Paths
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Solution Overview
Problem
Conventional low noise amplifiers require separate paths for different gain modes, increasing their size and complexity, and struggle to maintain performance factors like noise figure, phase discontinuity, and impedance matching across varying signal strengths.
Innovation Solution
A low noise amplifier design featuring a cascode structure with a gain controller that adjusts gain by varying current through a shared path, using transistors connected in a common source and common gate configuration, and incorporating matching networks and an inductor for impedance optimization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If separate paths are formed according to gain modes, then gain control is achieved, but the amplifier size increases
Solution Approach 1:
The patent merges multiple gain mode paths into a single shared path by placing the gain controller at the common connection point between the first and second transistors. This allows different gain modes to share the same signal path components (input matching network, transistors, output matching network), thereby reducing the overall amplifier size while maintaining adaptability for gain control.
Solution Approach 2:
The gain controller is designed to universally control gain across multiple operating modes by adjusting a single parameter (third transistor's control terminal voltage) that affects the entire amplification path. This multi-functional approach allows one controller to manage different gain modes without requiring separate control circuits for each path.
2Adaptability or versatility
If separate paths are formed according to gain modes, then gain adjustment is possible, but device complexity increases
Solution Approach 1:
The patent combines multiple gain mode paths into one shared path, reducing device complexity. Instead of having separate matching networks and switches for each gain mode, a single path is used with a gain controller that adjusts parameters to achieve different gain levels, thereby simplifying the overall device structure.
Solution Approach 2:
The patent achieves gain adjustment by changing electrical parameters (voltage applied to the third transistor's control terminal) rather than changing the physical path configuration. This parameter-based control simplifies the device structure compared to having multiple physical paths with separate matching networks and switches for each gain mode.
3Adaptability or versatility
If gain is adjusted by changing current in the amplification unit, then gain control is achieved, but noise figure may deteriorate
Solution Approach 1:
The patent introduces a third transistor as an intermediary element that controls the current flowing to the contact point between the first and second transistors. This intermediary allows gain adjustment without directly altering the main signal path's operating conditions, helping to maintain optimal noise figure while achieving gain control.
Solution Approach 2:
The patent adjusts gain by changing the current parameter in the amplification unit through the gain controller, while carefully managing the parameter changes to maintain optimal noise figure performance. The third transistor enables precise current control that achieves gain adjustment without significantly deteriorating the noise figure.
Data Source
AI summary
A low noise amplifier includes: an amplification unit including a first transistor and a second transistor connected in a cascode structure and configured to amplify a signal input to a control terminal of the first transistor; and a gain controller connected between a contact point at which the first transistor and the second transistor are connected to each other and a power source voltage, and configured to adjust a gain of the amplification unit.