RF Power Amplifier Envelope Tracking with Fast Transistor Rectification
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Solution Overview
Problem
Existing RF power amplifiers face challenges in achieving high linearity and efficiency due to the contradictory nature of these requirements, with conventional DC/DC converters being inefficient and parasitic elements reducing performance, especially in space applications where weight and cost are critical.
Innovation Solution
A RF power amplifier with envelope tracking using a fast DC/DC converter employing two RF power transistors as both the switching and rectifying elements, allowing for high commutation speed and handling of high currents and powers, thereby avoiding the diode bottleneck and minimizing parasitic components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional DC/DC converters are used for envelope tracking, then the circuit implementation is straightforward, but the efficiency is low and switching losses are unacceptable at high frequencies
Solution Approach 1:
The patent changes the fundamental operating parameters of the DC/DC converter by using a resonant topology that operates at the natural resonant frequency of the LC tank circuit. This allows the converter to achieve both high efficiency and high switching frequency (up to 80 MHz) simultaneously, overcoming the conventional trade-off where higher switching frequencies result in unacceptable losses.
Solution Approach 2:
The patent employs periodic resonant oscillations in the LC tank circuit to transfer energy. The switching transistor operates in conjunction with the resonant frequency, creating periodic energy transfer cycles that enable high-efficiency envelope tracking at high frequencies. The resonant action naturally limits switching losses while maintaining high switching rates.
2Productivity
If switching converters operate at high frequency (10-80 MHz) to follow fast envelope variations, then the envelope tracking bandwidth is sufficient, but conventional Si MOSFET circuits introduce unacceptable switching losses
Solution Approach 1:
The patent changes the switching mechanism from conventional hard switching to resonant soft switching. By operating the DC/DC converter at the resonant frequency of the LC tank, the transistor switches occur at optimal points in the resonant cycle, minimizing switching losses. This enables the system to achieve high envelope tracking bandwidth (up to 80 MHz) without the unacceptable switching losses that plague conventional high-frequency converters.
3Speed
If linear converters are used for envelope tracking, then the response speed is fast, but the efficiency is low
Solution Approach 1:
The patent replaces the linear conversion mechanism with a resonant switching mechanism. Instead of using linear regulation that dissipates excess power as heat, the system uses resonant energy transfer where the LC tank stores and releases energy efficiently. This substitution maintains the fast response characteristics of linear converters while achieving high efficiency through resonant energy transfer rather than linear dissipation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables high-efficiency envelope tracking with bandwidths of up to 36 MHz, eliminating the need for linear stages and reducing parasitic elements, thus enhancing performance and compactness while maintaining high efficiency across a wide range of output powers.
Implementation Method 1
The converter comprises a resonant LC circuit comprising an inductor L and a capacitor C
Implementation Method 2
The transistor of the DC/DC converter and that of the RF power amplifier are identical, discrete transistors embedded in a common package
Data Source
AI summary
A radio-frequency power amplifier with envelope tracking, comprising: a power RF amplifying device for amplifying a RF signal; and a switching DC/DC converter, comprising a switching device and a rectifying device, for providing said power RF amplifying device with a DC power supply at a voltage level proportional to an envelope of said RF signal; wherein said switching device is a RF power transistor; characterized in that said rectifying device, and preferably also said power RF amplifying device, is also a transistor of a same technology, connected as a two-terminal device. Preferably, said power RF amplifying device is also a transistor of said same technology. A low-pass filter can also be provided for reducing the bandwidth of the envelope signal on which the PWM signal driving the DC/DC converter depends.