Doherty RF Amplifier Peaking Gain Control for Lower Distortion
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Solution Overview
Problem
Doherty RF amplifier circuitry generates significant distortion when the peaking amplifier path becomes active due to parasitic impedances, which existing linearization techniques often fail to adequately compensate.
Innovation Solution
Incorporating a peaking variable gain preamplifier that adjusts the current provided to the peaking amplifier, allowing for adjustment of the output impedance and reducing distortion by controlling the gain of both the main and peaking amplifier paths through control circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the peaking amplifier path is activated to increase output power, then the power amplification capability is improved, but distortion is generated due to parasitic impedances
Solution Approach 1:
The patent changes the electrical parameters (impedance, current) of the peaking amplifier path dynamically. By adjusting the output impedance of the peaking amplifier path to match the real part of the input impedance of the main amplifier path, and by controlling the current through the peaking variable gain preamplifier, the system maintains power amplification while minimizing distortion generation at the transition point.
Solution Approach 2:
The patent employs control circuitry that monitors the operation state of the main and peaking amplifier paths and adjusts the peaking variable gain preamplifier accordingly. This feedback mechanism ensures that when the peaking amplifier path becomes active, its output impedance is properly adjusted to prevent distortion, and when it becomes inactive, the main amplifier path operates optimally.
2Reliability
If digital predistortion is used to compensate distortion, then linearity is improved, but the distortion may still be too large for adequate compensation
Solution Approach 1:
The patent takes preliminary action by pre-adjusting the output impedance of the peaking amplifier path before distortion becomes problematic. The control circuitry detects when the peaking amplifier path is about to become active and pre-adjusts its impedance to match the main amplifier path's input impedance, preventing distortion at its source rather than attempting to compensate for it afterward.
Solution Approach 2:
The patent converts the potentially harmful effect of parasitic impedances into a beneficial matching condition. By intentionally adjusting the peaking amplifier path's output impedance to match the main amplifier path's input impedance, the parasitic effects are transformed into a useful impedance matching relationship that minimizes distortion and improves power transfer efficiency.
3Power
If the peaking amplifier path operates in parallel with the main amplifier path, then power output is increased, but impedance mismatch causes distortion
Solution Approach 1:
The patent dynamically changes the impedance parameter of the peaking amplifier path to match the main amplifier path's input impedance. This parameter adjustment occurs at the transition point when the peaking amplifier path becomes active, ensuring that the parallel operation of both paths does not create harmful impedance mismatches that would generate distortion.
Data Source
AI summary
Doherty radio frequency (RF) amplifier circuitry includes an input node, an output node, a main amplifier path, and a peaking amplifier path. The main amplifier path is coupled between the input node and the output node and includes a main amplifier. The peaking amplifier path is coupled in parallel with the main amplifier path between the input node and the output node, and includes a peaking amplifier and a peaking variable gain preamplifier between the input node and the peaking amplifier. The peaking variable gain preamplifier is configured to adjust a current provided to the peaking amplifier.