Two-Stage RF Amplifier Topology for Low-Noise High Linearity
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Solution Overview
Problem
Current circuit topologies for wide band amplifiers fail to simultaneously achieve low noise, high linearity, reasonable power consumption, and acceptable input/output matching, leading to performance sacrifices or increased system costs in applications like TV/cable tuners.
Innovation Solution
A two-stage radio frequency wide band amplifier architecture is implemented, with the first stage providing high transconductance for low noise and the second stage offering a noiseless low impedance to limit output swing, utilizing PMOS and NMOS transistors with specific resistor configurations to achieve desired performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single stage amplifier is used to achieve low noise figure (3 dB), then noise performance is improved, but gain becomes too high (10-12 dB) causing distortion and linearity degradation
Solution Approach 1:
The amplifier is divided into two stages: first stage optimized for low noise figure with higher gain, and second stage optimized for linearity with lower gain. This segmentation allows each stage to perform its specialized function without compromising the other, achieving both low noise (3 dB) and acceptable linearity simultaneously
2Object-affected harmful factors
If gain is increased to achieve low noise figure, then noise performance is improved, but distortion increases causing linearity to deteriorate
Solution Approach 1:
The total gain is segmented between two stages with different optimization goals. The first stage provides higher gain (optimized for noise) while the second stage provides lower gain (optimized for linearity). This segmentation distributes the gain function to prevent any single stage from operating in a region that generates excessive distortion
Solution Approach 2:
Different quality characteristics are applied to different parts of the system: the first stage is designed with local quality optimized for low noise figure, while the second stage is designed with local quality optimized for linearity. This allows each stage to have the appropriate characteristics for its specific function
3Reliability
If conventional impedance is used to limit gain, then linearity is improved, but noise figure deteriorates due to resistor noise
Solution Approach 1:
The impedance control function is segmented: the first stage uses low impedance to limit gain and maintain linearity, while the second stage uses high impedance to minimize noise contribution. This segmentation allows each stage to have the appropriate impedance characteristic for its optimization goal without compromising the other
Data Source
AI summary
A radio frequency wide band amplifier having a noise that does not exceed a threshold value, and a linearity better than a threshold value. The radio frequency wide band amplifier architecture includes a first stage amplifier and a second stage amplifier. The second stage amplifier includes an input source resistor (Rin) that receives an input voltage signal, a feedback resistor (Rfb) directly connected to the input source resistor, a p-type metal-oxide-semiconductor (PMOS) transistor directly connected to the input source resistor. The PMOS transistor receives an output from the input source resistor. A n-type metal-oxide-semiconductor (NMOS) transistor directly connected to the input source resistor. The NMOS transistor receives an output from the input source resistor. A lumped output resistor (Rout) that receives an output from the feedback resistor, the PMOS transistor, and the NMOS transistor. A terminal of the lumped output impedance is connected to ground.