Doherty PA Base-Current Sensing for Antenna Impedance Tuning
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Solution Overview
Problem
In RF applications, the impedance presented by an antenna to a power amplifier is often not at a desired value, leading to poor receive sensitivity and degraded transmit performance due to factors like size constraints and proximity of the antenna to objects, resulting in a high voltage standing wave ratio (VSWR) that existing technologies struggle to compensate for effectively.
Innovation Solution
A power amplification system with a splitter and combiner circuit configuration using Doherty power amplifiers and a monitoring circuit to measure base currents, allowing for the adjustment of load impedance presented to the antenna, eliminating the need for a bi-directional coupler and utilizing cascode arrangements of transistors to predict and adjust antenna impedance based on base current ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a bi-directional coupler is used to measure forward and reflected power for antenna impedance prediction, then impedance measurement capability is provided, but insertion loss increases and receive sensitivity degrades
Solution Approach 1:
The patent extracts the impedance measurement function from the traditional bi-directional coupler approach and relocates it to the power amplifier's existing base current measurement nodes. By measuring base currents at the carrier and peaking amplifiers and computing their ratio, the system obtains antenna impedance information without inserting additional measurement hardware into the signal path, thereby eliminating the insertion loss associated with bi-directional couplers.
Solution Approach 2:
The patent uses base current as an intermediary parameter to indirectly measure antenna impedance. Instead of directly measuring forward and reflected power through a bi-directional coupler, the system measures the base currents of the carrier and peaking amplifiers, computes their ratio, and uses this ratio to determine antenna impedance. This intermediary measurement approach avoids the energy loss of direct power measurement hardware.
2Area of moving object
If antenna size is constrained to meet device form factors, then device compactness is improved, but antenna impedance matching deteriorates leading to high VSWR
Solution Approach 1:
The patent implements dynamic adjustment of the antenna matching network based on real-time base current ratio measurements. The system continuously monitors the ratio of carrier to peaking amplifier base currents, which reflects antenna impedance variations, and dynamically adjusts the matching network components (such as variable capacitors or inductors) to maintain optimal impedance matching despite antenna size constraints and environmental variations.
Solution Approach 2:
The patent establishes a feedback loop where the measured base current ratio is used to control the antenna matching network adjustment. The processor computes the base current ratio and generates control signals to adjust the matching network, creating a closed-loop system that automatically compensates for impedance mismatches caused by small antenna sizes or proximity to objects, thereby maintaining reliable impedance matching without increasing antenna physical dimensions.
3Reliability
If existing impedance compensation technologies are applied to high VSWR conditions, then some impedance adjustment is provided, but compensation effectiveness is insufficient and receive sensitivity remains degraded
Solution Approach 1:
The patent replaces traditional mechanical or fixed impedance measurement systems (bi-directional couplers with directional detectors) with an electronic measurement approach using base current sensing. By substituting the mechanical/electromagnetic measurement mechanism with electronic current measurement and digital computation of the base current ratio, the system achieves more precise impedance detection that is directly coupled to the power amplifier operation, thereby improving both compensation effectiveness and receive sensitivity without the losses associated with traditional measurement hardware.
Data Source
AI summary
Antenna impedance prediction via power amplifier parameter. In some embodiments, a power amplification system can include a splitter circuit and a combiner circuit, and first and second Doherty power amplifiers implemented in a quadrature configuration between the splitter circuit and the combiner circuit, with each Doherty power amplifier including a carrier amplifier and a peaking amplifier. The power amplification system can further include a monitoring circuit configured to measure at least some of base currents associated with the carrier and peaking amplifiers of the first and second Doherty power amplifiers, and generate a signal capable of adjusting a load impedance presented to an output of the combiner circuit.