MOSFET RF Output Circuit Using Gate Bias Power Adjustment
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Solution Overview
Problem
Existing RF power adjustment methods either require complex DDS circuits for broadband RF power supply or fixed switching power supply voltage, limiting flexibility and increasing control costs.
Innovation Solution
A power-adjustable RF output circuit that changes the gate bias voltage of a MOSFET to adjust RF power output without altering the RF input signal amplitude or drain supply voltage, using a RF frequency source transformer, operational amplifying module, relay, and filtering capacitors to control the gate bias voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If DDS is used to generate RF frequency source for broadband RF power supply, then RF power adjustment flexibility is improved, but device complexity and control cost increase
Solution Approach 1:
The patent extracts the RF frequency source generation function from the complex DDS system and implements it using a simple crystal oscillator with temperature compensation. This removes the unnecessary complexity while retaining the essential RF generation capability, directly resolving the contradiction between flexibility and complexity.
Solution Approach 2:
The patent replaces the expensive and complex DDS system with a simple, low-cost crystal oscillator circuit. This substitution achieves the same fundamental function (RF frequency generation) with dramatically reduced complexity and cost, addressing the technical contradiction.
2Reliability
If switching power supply voltage is made into fixed output for stability, then control ease and stability are improved, but RF power adjustment flexibility deteriorates
Solution Approach 1:
The patent changes the control parameter from drain voltage (which would require variable power supply) to gate bias voltage. By adjusting the gate bias voltage through the voltage divider circuit while keeping the drain supply voltage fixed, the system achieves RF power adjustment flexibility without compromising power supply stability.
3Ease of operation
If gate bias voltage is set to fixed value for simple control, then control ease is improved, but RF power adjustment capability deteriorates
Solution Approach 1:
The patent introduces a dynamic element (the relay-controlled voltage divider) into the gate bias circuit. This allows the gate bias voltage to be dynamically adjusted between different levels (including negative bias) while maintaining simple control through the relay switch, thus achieving both ease of operation and power adjustment capability.
Data Source
AI summary
A power-adjustable RF (radio frequency) output circuit is disclosed, which includes a RF frequency source transformer, wherein: one output end of the RF frequency source transformer is connected with a gate of a power amplifier module, another output end of the RF frequency source transformer is connected with a gate bias voltage control circuit; a source of the power amplifier module is connected with ground; the gate of the power amplifier module is connected with a resistor which is connected with ground, a drain of the power amplifier module is connected with a fixed voltage DC (direct current) power supply and also connected with a RF filtering network for outputting a RF power through the RF filtering network.