Power Measurement Circuit Using Transconductance Rectifier
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Solution Overview
Problem
Existing power measurement circuits for RF signals require a balun transformer for differential input, increasing cost and complexity, and often necessitate the true square of the input voltage to calculate average power, which is not always feasible.
Innovation Solution
A power measurement circuit utilizing a transconductance rectifier arrangement with an averaging filter to produce a time-averaged DC output signal proportional to the mean square of the input voltage, eliminating the need for a balun transformer and allowing single-ended input, suitable for signals with approximately 50% duty cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a balun transformer is used to interface single-ended RF signals with differential power measurement circuit input, then the circuit can measure power accurately, but the cost and circuit complexity increase
Solution Approach 1:
The patent extracts and eliminates the balun transformer from the circuit by redesigning the power measurement architecture to accept single-ended inputs directly. The differential input stage is replaced with a single-ended compatible rectifier configuration that processes the input signal without requiring differential transformation, thereby removing the complexity and cost of the balun while preserving measurement functionality.
Solution Approach 2:
Instead of converting single-ended to differential signals through a balun transformer (traditional approach), the patent inverts the approach by designing a rectifier that directly processes single-ended signals and generates the necessary differential output internally. This reversal of the signal conversion sequence eliminates the need for the balun component.
2Measurement precision
If a squaring cell with averaging RC filter is used to measure average power, then accurate power indication is achieved, but the circuit complexity and cost increase
Solution Approach 1:
The patent combines the squaring function and averaging function into a single integrated transconductance rectifier circuit. Rather than using separate squaring cell and RC filter components, the rectifier performs both operations simultaneously through its transfer characteristic and internal timing, reducing component count and circuit complexity while maintaining measurement accuracy.
Solution Approach 2:
The transconductance rectifier is designed to perform multiple functions: it rectifies the input signal, squares the voltage (through its non-linear transfer characteristic), and provides averaging (through its inherent timing and output characteristics). This multi-functional design eliminates the need for separate dedicated components for each function, simplifying the overall circuit.
3Measurement precision
If the circuit is optimized for 50% duty cycle signals, then measurement accuracy is improved, but the adaptability to other duty cycles decreases
Solution Approach 1:
The circuit is optimized for the common case of 50% duty cycle signals (partial optimization) where most RF applications operate, achieving high accuracy for this predominant scenario. The design accepts that accuracy may degrade for extreme duty cycles but provides sufficient performance for the vast majority of practical applications, representing a practical compromise between optimization and versatility.
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
The circuit provides accurate average power measurement without a balun transformer and can operate with single-ended inputs, maintaining square law conformance with minimal error across a wide dynamic range, making it suitable for RF applications.
Implementation Method 1
a transconductance rectifier arrangement including an input and configured to receive a periodically varying input voltage signal
Implementation Method 2
an averaging filter for producing a time averaged DC output signal proportional to the mean square of the voltage
Data Source
AI summary
A power measurement circuit and method are described. The circuit comprises: a transconductance rectifier arrangement including an input and configured to receive a periodically varying input voltage signal having an approximate 50% duty cycle; and an averaging filter for producing a time averaged DC output signal proportional to the mean square of the voltage at the input of the transconductance rectifier arrangement and representative of the average power of the input voltage signal within a range of voltages at the input.