RF Impedance Measurement Circuit for Accurate Millimeter-Wave Phase Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing RF impedance measurement circuits are not suitable for high-frequency applications, such as the millimeter-wave range, due to amplitude-dependent errors and loading effects that degrade phase detection accuracy.
Innovation Solution
An RF impedance measurement circuit with a sensing capacitor connected in series to the RF signal path, coupled with amplitude detectors and frequency dividers to maintain constant amplitude and enable accurate phase detection, along with phase detection circuits to reconstruct phase differences, minimizing loading effects and amplitude-dependent delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If log amplifier is used for amplitude detection, then amplitude detection is achieved, but amplitude-dependent delay causes excessive error to phase detection especially at higher frequencies
Solution Approach 1:
The patent extracts the problematic log amplifier from the signal path and replaces it with a combination of amplitude detector and frequency divider. This separation removes the source of amplitude-dependent delay while preserving the necessary amplitude detection function, thereby eliminating the phase detection error caused by the log amplifier's non-linear characteristics.
Solution Approach 2:
The patent changes the operational parameters by using frequency dividers with fixed division ratios instead of log amplifiers with variable gain. This parameter change transforms the system from one with amplitude-dependent timing characteristics to one with fixed timing relationships, eliminating the amplitude-dependent delay that degrades phase measurement accuracy at high frequencies.
2Measurement precision
If sensing capacitor is connected in series with RF signal path, then impedance measurement is enabled, but loading effect degrades output power linearity and efficiency
Solution Approach 1:
The patent applies local quality by making the sensing capacitor's loading effect localized and controlled. By positioning the sensing capacitor specifically in series with the RF signal path and designing it with appropriate capacitance values, the loading effect is confined to a minimal impact on the overall power amplification chain, preserving output power linearity while enabling impedance measurement functionality.
Solution Approach 2:
The patent uses a sensing capacitor with small but non-negligible capacitance value that provides sufficient measurement signal coupling while maintaining negligible loading effect. This partial action approach allows the capacitor to perform its measurement function without excessively interfering with the RF signal power transmission, thus maintaining output power linearity and efficiency.
3Measurement precision
If frequency divider is used instead of log amplifier, then amplitude-dependent delay is avoided, but circuit complexity increases
Solution Approach 1:
The patent introduces frequency dividers as intermediary components between the RF signal path and the phase detection circuitry. These frequency dividers act as mediators that convert the RF signal to lower frequency while maintaining fixed timing relationships, thereby avoiding the amplitude-dependent delay of log amplifiers. The intermediary structure, while adding components, provides superior phase measurement accuracy through deterministic timing characteristics.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An RF impedance measurement circuit (100), comprises a sensing capacitor (104) connectable in series with an RF signal path (102); a first amplitude detector (116a) and a first frequency divider (108a), each coupled, with said measurement circuit in operation, to said RF signal path (102) at a first terminal (104a) of said sensing capacitor (104); a second amplitude detector (116b) and a second frequency divider (108b), each coupled, with said measurement circuit in operation, to a second terminal (104b) of said sensing capacitor (104); and a phase detection circuit (110a) connected to an output (I) of said first frequency divider (108a) and to an output (I) of said second frequency divider (108b).