Bipolar Cascode Power Amplifier for Stable Envelope-Tracking Gain
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Solution Overview
Problem
Power amplifying modules employing envelope tracking schemes face gain variation issues due to varying base-collector capacitance with power supply voltage, leading to degradation in linearity.
Innovation Solution
A power amplifying module configuration using a cascode amplifier circuit with a first bipolar transistor having a grounded emitter and a second bipolar transistor with a constant base voltage, where the power supply voltage varies with the amplitude of the RF signal, reducing the impact of power supply voltage on gain variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If envelope tracking scheme is used to reduce power consumption, then power efficiency is improved, but gain variation occurs due to base-collector capacitance changing with power supply voltage
Solution Approach 1:
The power amplifying module is divided into two separate bipolar transistors: a first bipolar transistor for providing a stable base-collector capacitance (with grounded emitter) and a second bipolar transistor for power amplification (with constant base voltage). This segmentation allows each transistor to perform its specific function independently, preventing gain variation while enabling envelope tracking for power efficiency.
Solution Approach 2:
The first bipolar transistor acts as an intermediary element between the power supply and the second bipolar transistor. By placing the first transistor in series with the collector of the second transistor, it mediates the effect of power supply voltage variations on the base-collector capacitance, isolating the amplification process from power supply fluctuations.
2Loss of energy
If power supply voltage is varied to reduce power loss, then energy efficiency is improved, but linearity degrades due to gain variation
Solution Approach 1:
The module segments the power amplification function into two transistors with distinct roles: the first transistor maintains stable capacitance characteristics while the second performs amplification. This allows power supply voltage to be varied for energy efficiency without causing gain variation, preserving linearity.
Solution Approach 2:
The invention changes the configuration parameters of the bipolar transistors, specifically the emitter connections (grounded for first transistor, connected to second transistor collector for second transistor) and base voltage conditions (variable for first transistor, constant for second transistor). These parameter changes enable the system to achieve both energy efficiency and linearity.
Data Source
AI summary
The linearity of a power amplifying module employing an envelope tracking scheme is improved. The power amplifying module includes a first bipolar transistor having a base to which a first radio frequency signal is input and an emitter grounded, and a second bipolar transistor having a base to which a first constant voltage is applied, a collector to which a first power supply voltage is applied, the first power supply voltage adapted to vary in accordance with an amplitude of the first radio frequency signal, and an emitter connected to a collector of the first bipolar transistor. The second bipolar transistor is configured to output a first amplified signal, obtained by amplifying the first radio frequency signal, from the collector of the second bipolar transistor.