Cascode Bias Circuit for Power Amplifier Phase Linearity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Power amplifiers in mobile communication devices, particularly those using millimeter wave signals, face challenges in maintaining phase linearity across multiple power levels due to cascode transistor operation in saturation and triode modes, leading to significant phase distortion and non-linear phase behavior.
Innovation Solution
A bias circuit is implemented to fix the bias of cascode transistors within power amplifiers, allowing them to operate at a fixed duty cycle between saturation and triode modes, resulting in constant capacitance and negligible phase distortion across a wide signal level range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If cascode transistors operate in saturation and triode modes across multiple power levels, then power amplification capability is improved, but phase linearity deteriorates due to significant phase distortion
Solution Approach 1:
The bias voltage applied to the cascode transistor gate is dynamically adjusted based on the operating power level. At different power levels, the bias voltage changes to maintain a substantially constant duty cycle (e.g., 50%) of triode mode operation, thereby maintaining constant average capacitance and improving phase linearity across the full power range while preserving power amplification capability
Solution Approach 2:
The invention changes the bias voltage parameter of the cascode transistor to control the duty cycle of triode mode operation. By adjusting this parameter, the average capacitance is kept constant across multiple power levels, which directly addresses the phase linearity issue while maintaining the ability to amplify across different power levels
2Manufacturing precision
If cascode transistors are biased to operate at fixed duty cycle in triode mode, then phase distortion is reduced through constant capacitance, but circuit complexity increases due to bias circuitry
Solution Approach 1:
The bias circuit is designed to automatically adjust the gate bias voltage based on the operating conditions to maintain the desired duty cycle. The circuit self-regulates to keep the average capacitance constant, reducing phase distortion without requiring complex external control systems or additional components beyond the integrated bias circuitry
3Adaptability or versatility
If cascode transistors operate with varying capacitance across power levels, then power amplification range is improved, but phase distortion increases making correction difficult
Solution Approach 1:
Instead of allowing capacitance to vary freely with power level, the invention dynamically adjusts the bias voltage to maintain a constant duty cycle of triode mode operation. This dynamic control keeps the average capacitance substantially constant across the power amplification range, thereby maintaining phase linearity while preserving the ability to amplify across multiple power levels
Data Source
AI summary
Amplitude modulation-phase modulation (AM-PM) linearization in a power amplifier using bias circuitry, which fixes a bias of a cascode transistor within a power amplifier is disclosed. In particular, the cascode transistor may switch between operation in a saturation mode and a triode mode. The bias is set such that the cascode transistor operates at a fixed duty cycle in the triode mode relative to the saturation mode for a wide range of signal levels from small-signal to large-signal. An exemplary duty cycle is fifty percent (50%), although other duty cycles may be used. This bias will result in a constant capacitance contributed by the cascode device to the power amplifier over a wide signal level range.