RF Pulse Switching Circuit With Fast Fall Time and Low Noise
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Solution Overview
Problem
Conventional RF pulse signal generation circuits for target object detecting apparatuses, such as radar systems, face challenges in rapidly falling waveforms and stability issues due to the use of p-type FETs for high-side switching, leading to reduced receiving sensitivity and increased transmission noise in close-range detection.
Innovation Solution
The RF pulse signal generation switching circuit employs n-type FETs for both low-side and high-side control, utilizing a capacitor to supply gate current to the high-side FET, ensuring rapid fall times and stable operation by compensating the gate-source voltage, and includes a gate voltage controller to synchronize gate and drain voltage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a p-type FET is used as a high-side FET in the drain switching circuit, then the circuit structure is simple, but the fall time becomes long and receiving sensitivity degrades
Solution Approach 1:
The patent changes the key parameter of FET type from p-type to n-type for the high-side switching element. This parameter change fundamentally improves the fall time characteristic because n-type FETs have higher electron mobility and can discharge the output capacitance much faster than p-type FETs, directly resolving the speed contradiction while maintaining circuit simplicity through the same basic switching topology.
Solution Approach 2:
The patent introduces a preliminary action by adding a discharge path that becomes active before the main switching action is needed. The discharge transistor and discharge capacitor create a pre-configured fast discharge path that can immediately pull the output low when needed, preparing the circuit state in advance to achieve rapid fall times without complicating the main switching structure.
2Speed
If an operational amplifier with high unity gain frequency is used to control gate voltage, then the fall time is shorter, but output waveform ringing occurs and stability is low
Solution Approach 1:
The patent replaces the operational amplifier-based voltage control system with a direct transistor switching system. Instead of using an op-amp to control the gate voltage (which causes ringing due to its high-speed characteristics), the invention uses a transistor switch that directly controls the drain voltage. This substitution eliminates the ringing problem while achieving fast fall times through the transistor's inherent switching capability.
Solution Approach 2:
The patent introduces an intermediary element - the discharge transistor - that mediates between the control signal and the output. This intermediary provides a controlled discharge path that prevents the direct high-speed switching that causes ringing in op-amp circuits, while still achieving fast fall times through the transistor's switching action. The intermediary smooths the transition and improves stability.
3Device complexity
If the drain voltage of the power FET is controlled using conventional drain switching circuit, then the circuit is simple, but transmission noise increases and receiving sensitivity degrades in close-range detection
Solution Approach 1:
The patent applies preliminary action by pre-configuring a fast discharge path using the discharge transistor and discharge capacitor. This discharge path is ready before transmission ends and can immediately pull the drain voltage low when the transmission stops, preventing the tailing effect that causes transmission noise. This preliminary preparation allows the circuit to maintain simplicity while dramatically reducing noise and improving close-range receiving sensitivity.
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
This configuration enables rapid fall times for RF pulse signals, reducing transmission noise and improving receiving sensitivity, especially in close-range target object detection.
Implementation Method 1
a capacitor to supply gate current to the high-side FET, ensuring rapid fall times and stable operation by compensating the gate-source voltage
Data Source
AI summary
An RF pulse signal generation switching circuit for controlling an output of a power FET for amplifying a high frequency signal to generate an RF pulse signal that is the high frequency signal pulse formed into a pulse-wave shape is provided. The circuit includes first and third n-type FETs of which gates are inputted with a control pulse that supplies a rise timing and a fall timing of a pulse, and a second n-type FET of which a gate is connected with a drain of the first FET. A source of the first FET and a source of the third FET are grounded, respectively. The drain of the first FET is applied with a first drive voltage via a resistor. A drain of the second FET is applied with a second drive voltage. A source of the second FET is connected with a drain of the third FET and the connection point therebetween is connected with the power FET. A capacitor is connected between the connection point and an end of the resistor from which the first drive voltage is applied.