Two-Stage RF Power Amplifier Bias Network for Gain Compression
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Solution Overview
Problem
The linearity of power amplification modules degrades as output power increases, leading to a decrease in gain and efficiency in mobile communication devices.
Innovation Solution
A power amplification module with a two-stage amplification circuit and bias circuit configuration, where the bias circuit includes a third transistor, capacitors, and resistors to optimize bias current supply and RF signal input, enhancing the linearity by controlling impedance changes and increasing bias current at high signal levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the power amplification module operates at high output power levels, then the output power increases, but the gain decreases and linearity degrades
Solution Approach 1:
The bias circuit dynamically adjusts the bias current based on the RF signal level. At high signal levels, the bias current increases automatically through the action of the capacitor and resistor network, allowing the amplifier to maintain linearity across varying output power levels. This dynamic adaptation resolves the contradiction between high output power and maintained linearity.
Solution Approach 2:
The invention changes the operating parameters of the bias circuit by introducing a capacitor connected to the RF signal and a network of resistors that modify the bias current characteristics. These parameter changes enable the bias current to vary with signal level, improving linearity at high output powers while maintaining stable operation across the full power range.
2Reliability
If the bias current is increased to maintain linearity at high power levels, then the linearity improves, but the power consumption increases
Solution Approach 1:
The bias circuit uses dynamic control where the bias current is adjusted according to the instantaneous RF signal level rather than being constantly high. The capacitor couples the RF signal to the bias network, causing the bias current to increase only when needed at high signal levels, thereby maintaining linearity without continuous high power consumption.
Solution Approach 2:
The bias current modulation occurs periodically in response to the RF signal cycles. The capacitor charges and discharges with the RF signal, creating periodic variations in bias current that coincide with high signal levels, thus improving linearity only when necessary and reducing overall power consumption.
Data Source
AI summary
A power amplification module includes: a first transistor that amplifies a first radio frequency signal and outputs a second radio frequency signal; a second transistor that amplifies the second radio frequency signal and outputs a third radio frequency signal; and first and second bias circuits that supply first and second bias currents to bases of the first and second transistors. The first bias circuit includes a third transistor that outputs the first bias current from its emitter or source, a capacitor that is input with the first radio frequency signal and connected to the base of the first transistor, a first resistor connected between the emitter or source of the third transistor and the base of the first transistor, a second resistor connected between the capacitor and the emitter or source of the third transistor, and a third resistor connected between the capacitor and the base of the first transistor.