RF Power Sensing Circuit for Load-Independent Output Measurement
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Solution Overview
Problem
Existing RF power amplifier power sensing methods, such as directional and bidirectional couplers, and mirror transistors, fail to provide accurate power measurements due to load impedance variations and phase mismatches, leading to potential damage from excessive current or voltage peaks.
Innovation Solution
An electronic circuit that directly senses RF current and voltage using a scaled-down transistor and a low-capacitance voltage sensing module, with a coherent detector like a Gilbert quad to multiply these signals, generating an instantaneous power signal independent of load impedance, allowing for effective load mismatch detection and control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If directional or bidirectional couplers are used for power sensing, then RF power delivery and reflection can be sensed, but measurement precision deteriorates when load impedance varies
Solution Approach 1:
The patent replaces the traditional coupler-based sensing system with a transistor-based sensing system. The first transistor senses RF current directly at the output, and the second transistor senses RF voltage, eliminating the need for couplers. This substitution allows accurate power measurement independent of load impedance variations because the transistors directly sample the electrical parameters without being affected by impedance mismatches.
Solution Approach 2:
The patent introduces a capacitor as an intermediary element to couple the sensing circuitry to the output terminals. This capacitor enables voltage sensing without directly loading the output, and the transistor-based sensing acts as an intermediary that converts RF current and voltage into measurable signals for power calculation, isolating the measurement system from load variations.
2Measurement precision
If couplers are used for power sensing, then power reflection can be detected, but device size increases
Solution Approach 1:
The patent extracts the essential power sensing function from the complex coupler structure and implements it using simple transistor-based sensing elements. By taking out only the necessary current and voltage sensing capabilities and implementing them with transistors and capacitors, the solution achieves power sensing without the bulky coupler components.
Solution Approach 2:
The patent changes the sensing approach from using couplers that require specific impedance matching to using transistors that can directly sense current and voltage parameters. This parameter change in the sensing methodology allows for compact implementation while maintaining the ability to detect both delivered and reflected power through direct electrical measurement.
3Volume of moving object
If mirror transistors are used for current sensing, then device size is reduced, but measurement precision deteriorates due to phase mismatch
Solution Approach 1:
The patent segments the power sensing function into two independent sensing paths: one for current (using the first transistor) and one for voltage (using the second transistor). Each transistor is optimized for its specific sensing function, and the individual current and voltage measurements are then combined to calculate power. This segmentation eliminates the phase mismatch problem that plagues mirror transistor approaches because each sensing element operates independently without requiring phase coherence.
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 provides an accurate and instantaneous measure of RF power delivered to a load, preventing excessive current or voltage peaks and enabling precise power control, thus extending the lifespan of the RF power amplifier.
Implementation Method 1
a first transistor for sensing the current of an output of the power amplifier and for providing a scaled-down copy of a RF current signal
Implementation Method 2
coupling an appropriate sensing circuitry to the output terminals by means of a capacitor featuring a very low capacitance
Implementation Method 3
a coherent detector that is adapted to multiply the RF voltage signal and the RF current signal
Data Source
AI summary
The present invention provides an electronic circuit for measuring of an output power of a RF power amplifier. The electronic circuit comprises a current sensing transistor for sensing the RF current of the power amplifier and a voltage sensing module for sensing the voltage of the RF power amplifier. The electronic circuit further comprises a coherent detector for multiplying the sensed current and the sensed voltage in the time domain. In this way a signal is generated that is directly indicative of the power provided by the power amplifier irrespective of its actual load. Preferably, the coherent detector is implemented as a Gilbert quad and provides a differential output that effectively allows for DC offset compensation.