MOSFET RF Power Detector Calibration for High-Frequency Accuracy
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Solution Overview
Problem
Existing FET/MOS power detectors face performance deterioration due to carrier mobility degradation, particularly at high frequencies, which affects the accuracy of signal strength indication and automatic gain control in radio communication systems.
Innovation Solution
A FET RF signal detector circuit is designed using two unbalanced differential transistor pairs with variable resistors between branch tails, allowing for improved calibration and high-frequency operation, enabling a logarithmic amplifier structure that compensates for mobility effects and provides a wide dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If FET/MOS power detectors are used at high frequencies, then integration with digital calibration and cost efficiency are improved, but carrier mobility degradation causes performance deterioration
Solution Approach 1:
The patent changes the operating parameters of the FET detector by introducing a specific mathematical relationship between the transconductances of the differential pair transistors (g_m1/g_m2 = K) and using the MOSFET's intrinsic square-law characteristic in saturation mode. This parameter configuration enables the detector to maintain accurate power detection despite carrier mobility degradation, as the circuit is designed to be independent of mobility variations.
Solution Approach 2:
The patent uses the intrinsic square-law characteristic of MOSFETs in saturation mode to directly implement power detection without requiring complex bipolar transistor-based squaring circuits. By copying and utilizing the natural MOSFET behavior, the design achieves accurate power detection with simpler circuitry that is inherently more robust to process variations and mobility degradation.
2Speed
If channel length is decreased to follow technology node trends, then transistor speed and integration density are improved, but carrier mobility degradation increases
Solution Approach 1:
The patent designs the differential pair with specific transconductance ratios (g_m1/g_m2 = K) and operates the MOSFETs in saturation mode where the square-law characteristic dominates. This parameter configuration makes the detection accuracy independent of carrier mobility, allowing the circuit to function accurately even as channel length decreases and mobility degrades in scaled technologies.
Solution Approach 2:
The patent converts the harmful effect of carrier mobility degradation into a benefit by designing a circuit that exploits the intrinsic square-law characteristic of MOSFETs. The design intentionally uses the MOSFET's natural behavior in saturation mode, where power detection accuracy becomes independent of mobility variations, thereby turning a potential source of error into a robust design feature.
3Measurement precision
If bipolar transistor based detectors are used, then power detection is achieved, but complex circuitry is required to extrapolate the square function
Solution Approach 1:
The patent copies and utilizes the intrinsic square-law characteristic of MOSFETs in saturation mode to implement power detection. By doing so, the circuit naturally produces a signal proportional to the input power without requiring additional squaring circuits, significantly reducing complexity compared to bipolar implementations that need external squaring functionality.
Solution Approach 2:
The patent extracts and utilizes the square-law characteristic that is inherently present in MOSFET operation, removing the need for separate squaring circuitry. This extraction of the essential functional element from the device physics simplifies the overall circuit architecture while maintaining accurate power detection capability.
Data Source
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AI summary
The invention provides an FET RF signal detector circuit comprising two unbalanced differential transistor pairs, each having at least one variable resistor between a pair of tails of the differential pair. This provides improved circuit performance as well as enabling a calibration function.