RF Amplifier Gain Reduction Without Noise Figure Degradation
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Solution Overview
Problem
Designing a radio-frequency amplifier for electronic devices with multiple gain modes that maintains noise figure and frequency response across a wide range of frequency bands is challenging, as existing amplifiers either degrade noise performance or alter frequency response when adjusting gain.
Innovation Solution
The radio-frequency amplifier includes input and capacitance neutralization transistors cross-coupled with gain adjustment switches that can be selectively activated or deactivated to operate in high and low gain modes, allowing out-of-phase current to flow through capacitance neutralization transistors, thereby reducing gain without impacting noise figure or frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If gain adjustment is implemented in conventional radio-frequency amplifiers, then gain attenuation is achieved, but noise figure and frequency response are degraded
Solution Approach 1:
The amplifier implements dynamic gain adjustment by selectively activating or deactivating specific transistors (first and second transistors in parallel with third and fourth transistors) based on the desired gain mode. This dynamic reconfiguration allows the amplifier to switch between high gain mode (only first and second transistors active) and low gain mode (all four transistors active), adapting the circuit topology to achieve different gain levels while maintaining optimal noise figure and frequency response characteristics for each mode.
2Reliability
If a single gain mode is used, then noise figure and frequency response are optimized, but gain adaptability is limited
Solution Approach 1:
The amplifier circuit is segmented into multiple parallel transistor branches: first and second transistors for high gain operation, and third and fourth transistors for low gain operation. By segmenting the amplification function across these separate transistor pairs and selectively enabling/disabling them, the amplifier achieves multiple gain modes (high gain and low gain) while maintaining optimized noise figure and frequency response characteristics in each segment, thereby expanding gain adaptability without sacrificing performance.
Data Source
AI summary
An electronic device may include wireless circuitry with a processor, a transceiver, an antenna, and a front-end module coupled between the transceiver and the antenna. The front-end module may include one or more radio-frequency amplifiers for amplifying a radio-frequency signal. The radio-frequency amplifier may include input transistors cross-coupled with capacitance neutralization transistors and/or coupled to cascode transistors. One or more n-type gain adjustment transistors may be coupled to source terminals of the capacitance neutralization transistors. One or more p-type gain adjustment transistors may be coupled to source terminals of the cascode transistors. One or more processors in the electronic device can selectively activate one or more of the gain adjustment transistors to reduce the gain of the radio-frequency amplifier without degrading noise performance and without altering the in-band frequency response of the radio-frequency amplifier.