RF Impedance Sensing Circuit Using Frequency Dividers for Phase Accuracy
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Solution Overview
Problem
RF impedance measurement circuits are not suitable for high-frequency applications, such as the millimeter-wave range, due to amplitude-dependent delays caused by log amplifiers, leading to errors in phase detection and inefficiencies in RFIC designs.
Innovation Solution
An RF impedance measurement circuit with a sensing capacitor, amplitude detectors, frequency dividers, and phase detection circuits that maintain phase information while eliminating amplitude variations, allowing for accurate phase detection at high frequencies, and includes a voltage divider to protect downstream circuits from large output powers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a log amplifier is used for amplitude detection in RF impedance measurement, then the circuit can operate at lower frequencies, but amplitude-dependent delays cause excessive error in phase detection at higher frequencies
Solution Approach 1:
The patent extracts and removes the log amplifier component from the measurement circuit. Instead of using a log amplifier that introduces amplitude-dependent delays, the invention uses a different detection mechanism that directly measures phase difference without being influenced by amplitude variations, thereby eliminating the source of measurement error at high frequencies
Solution Approach 2:
The patent substitutes the log amplifier-based detection mechanism with a direct phase detection mechanism. The new approach replaces the amplitude-based measurement method with a phase-based method that is insensitive to amplitude variations, effectively substituting a flawed measurement system with a robust one suitable for high-frequency operation
2Measurement precision
If an RF impedance measurement circuit is connected in series with the RF signal path, then impedance measurement is enabled, but the circuit loads the signal path and reduces output power and efficiency
Solution Approach 1:
The patent applies local quality by making the sensing capacitor's capacitance value locally optimized for minimal impact. By carefully selecting the capacitance value of the sensing capacitor, the circuit achieves minimal loading effect on the specific RF signal path, allowing impedance measurement while preserving output power and efficiency characteristics
3Power
If the sensing capacitor has larger capacitance to reduce loading effect, then output power and linearity are maintained, but measurement accuracy decreases
Solution Approach 1:
The patent uses parameter changes by optimizing the capacitance value of the sensing capacitor. Through careful selection and adjustment of this critical parameter, the circuit achieves an optimal balance where the loading effect is minimized enough to maintain power and linearity, while the capacitance remains sufficiently large to provide accurate impedance measurement
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
Enables accurate RF complex impedance measurement at high frequencies with reduced errors and maintains output power linearity and efficiency by avoiding amplitude-dependent delays, thus extending the circuit's operational range into the millimeter-wave range.
Implementation Method 1
a first frequency divider and a second frequency divider, each coupled, with the measurement circuit in operation, to the RF signal path
Implementation Method 2
the phase detection circuit is a mixer configured to mix the output of the first frequency divider and the output of the second frequency divider
Implementation Method 3
through an appropriate choice of the capacitance of the sensing capacitors, this arrangement may provide a negligible loading effect to the circuits driving the RF signal path
Data Source
AI summary
An RF impedance measurement circuit includes a sensing capacitor connectable with an RF signal path; a first amplitude detector and a first frequency divider, each coupled, with the measurement circuit in operation, to the RF signal path at a first terminal of the sensing capacitor; a second amplitude detector and a second frequency divider, each coupled, with the measurement circuit in operation, to a second terminal of the sensing capacitor; and a phase detection circuit connected to an output of the first frequency divider and to an output of the second frequency divider.