CMOS RF Power Limiter Anti-Parallel FET Configuration
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Solution Overview
Problem
Conventional transceivers in wireless communications systems, particularly those using CMOS technology, face challenges with excessive voltage stress on transistors due to insufficient power limiting, leading to potential damage and unreliable operation, especially when connected to automatic test equipment.
Innovation Solution
A CMOS RF power limiter circuit utilizing two NMOS FETs in an anti-parallel configuration, which acts as diodes to symmetrically attenuate RF signals when they exceed a defined forward voltage, providing effective power limiting without requiring bias current or additional matching circuitry, and can be integrated into transceiver circuits or used as standalone devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional transceiver architectures are used without power limiting circuits, then device complexity is reduced, but voltage stress on transistors increases causing reliability degradation
Solution Approach 1:
The patent combines the power limiting function with the existing transceiver architecture by integrating limiter circuits at the input stage of the power amplifier. This merging approach adds protection functionality without creating a completely separate system, thereby improving transistor reliability while minimizing the increase in overall device complexity.
Solution Approach 2:
The patent introduces intermediary power limiting circuits that act as mediators between the transceiver and the power amplifier. These intermediary circuits attenuate excessive input signals before they reach the power amplifier transistors, preventing voltage stress and reliability degradation without requiring fundamental changes to the main transceiver architecture.
2Power
If input power to power amplifier is increased for calibration mode, then transceiver output power increases, but voltage stress on transistors increases causing reliability degradation
Solution Approach 1:
The patent applies local quality control by implementing power limiting specifically at the input stage of the power amplifier where the voltage stress is most critical. The limiter circuits are positioned to provide localized attenuation exactly where needed, allowing high output power operation while protecting the most vulnerable transistors from excessive voltage stress.
Solution Approach 2:
The patent employs dynamic power limiting that adapts to different operating conditions. The limiter circuits automatically adjust their attenuation characteristics based on the input signal level, providing minimal attenuation during normal operation to maintain high output power capability, and increasing attenuation during calibration mode or overload conditions to protect transistor reliability.
3Ease of manufacture
If CMOS technology is used for transceiver, then manufacturing cost is reduced, but breakdown voltage rating of transistors decreases making them more susceptible to damage
Solution Approach 1:
The patent implements beforehand cushioning by placing power limiting circuits in advance of the CMOS power amplifier stage. These limiter circuits provide protective attenuation before excessive voltage signals can reach the CMOS transistors, cushioning them against voltage stress and potential breakdown. This approach allows the use of cost-effective CMOS technology while compensating for its lower breakdown voltage rating.
Solution Approach 2:
The patent converts the inherent vulnerability of CMOS transistors to voltage stress into a benefit by designing the power limiting circuits specifically to protect this weakness. The lower breakdown voltage rating of CMOS devices becomes a design driver that ensures adequate protection is built in, making the overall system more robust against input power variations and potential damage sources.
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 solution effectively mitigates voltage and current over-stress on transistors, ensuring reliable operation while consuming less area and not necessitating additional components, and can handle RF signals up to 5 GHz, offering improved power limiting and ESD protection capabilities.
Implementation Method 1
A first and second CMOS FETs may be configured to perform a diode function with a defined forward voltage and arranged in an anti-parallel configuration
Implementation Method 2
arranged in an anti-parallel configuration and coupled between the input terminal and the ground terminal. When an RF signal is applied symmetrically to the input terminal and ground terminal it becomes symmetrically attenuated
Data Source
AI summary
An RF power limiter and ESD protection circuit has a set of two CMOS FETs each configured to perform a diode function with a defined forward voltage and arranged in an anti-parallel configuration and coupled between the input terminal and the ground terminal. When an RF signal is applied symmetrically to the input terminal and ground terminal it becomes symmetrically attenuated when the signal level exceeds the defined forward voltage of the diode configured CMOS FETs. In the ESD protection mode one of the CMOS FETs acts as a grounded gate NMOS transistor with SCR action to provide for mitigation of voltage and current over-stress of transistors utilized in RF transceiver circuits. Generally, the circuit architectures allow input power levels to be limited to an extent that reliable operation can be maintained.