Feedforward Linearizer Current Referencing for Wide-Temperature RF Linearity
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Solution Overview
Problem
Conventional feedforward linearizers for RF amplifiers are not effective over a broad temperature range, as their linearization effectiveness is limited to a small temperature range due to the temperature dependence of intermodulation distortion, which reduces the dynamic range of the amplifier.
Innovation Solution
A temperature-compensated feedforward linearizer is designed by splitting the reference node between the main and linearizing amplifiers and using a second reference generator to match the thermal coefficient of the linearizing amplifier to the intermodulation distortion, allowing for optimal linearizing amplifier output current across a range of temperatures, measured by the 3rd order output intercept point (OIP3), and configuring the linearizing amplifier with a tunable current source to achieve peak linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a standard or bandgap current reference generator is used in the feedforward linearizer, then the linearization effectiveness is improved at a specific temperature, but the temperature range over which the linearizer remains effective is limited to a relatively small range
Solution Approach 1:
The patent divides the single reference generator into two separate reference generators: a first reference generator coupled to the main amplifier and a second reference generator coupled to the linearizing amplifier. This segmentation allows each reference generator to be independently optimized for different temperature characteristics, enabling the linearizer to maintain effectiveness across a broad temperature range while preserving linearization precision at any given temperature
Solution Approach 2:
The patent applies different temperature compensation characteristics to different parts of the system. The second reference generator is specifically designed to compensate for temperature-dependent variations in the linearizing amplifier's intermodulation distortion, while the first reference generator maintains the main amplifier's operating point. This local quality differentiation enables each amplifier to operate optimally across temperature variations
2Power
If the input power to the RF amplifier is increased, then the output power and signal strength are improved, but the intermodulation distortion increases, thereby reducing the dynamic range of the amplifier
Solution Approach 1:
The patent implements preliminary anti-action by using the linearizing amplifier to pre-compensate for intermodulation distortion before it degrades the output signal. The linearizing amplifier is configured to generate an inverted version of the distortion components and inject them into the main amplifier's output, thereby canceling the harmful intermodulation products and preserving dynamic range even at high output power levels
Data Source
AI summary
A feedforward linearizer device is disclosed. The device includes a main amplifier, and a linearizing amplifier operatively coupled to the main amplifier. A first reference generator is operatively coupled to the main amplifier by a first reference node. A second reference generator is operatively coupled to the linearizing amplifier by a second reference node, and is configured to cause an optimal linearizing amplifier output current for each of a plurality of temperatures. In one such case, the second reference generator is configured to cause an optimal linearizing amplifier output current for each of a plurality of temperatures based on a corresponding optimal ratio of main amplifier output current and linearizing amplifier output current. The linearizing amplifier may be configured with a tunable current source that is controlled by the second reference generator, or a current source having a fixed total transistor area (not tunable).