In an RF system, there are typically multiple input and output ports, making it costly to analyze scattering characteristics using a multi-port network analyzer. Therefore, it is common to use a switch to route signals between multiple inputs and outputs, allowing analysis with a simpler two-port network analyzer. In nuclear magnetic resonance (NMR) systems, the number of receiving channels is often fewer than the number of antenna coils, so multi-loop coils must be switched to select and use the appropriate ones.
Currently, most designs rely on ready-made switch chips for this function. However, these chips are often unreliable, prone to damage, and require complex power supply setups. For instance, the SW-437 chip, while capable of basic switching, has high static electricity requirements that are difficult to meet in standard lab or workshop environments, leading to frequent failures and inconvenient practical use. To address this, a new RF switch conversion circuit using PIN diodes has been designed. This circuit allows selection of any two RF signal outputs from four available inputs.
The switch will be integrated into a resonant test system based on the LabView platform. The computer provides a voltage control signal, which is a digital signal with high and low levels (5V and 0V). Since the RF switch requires 10V for operation, a voltage conversion circuit is necessary. The entire system consists of two main parts: a voltage conversion circuit and an RF switching circuit. When LabView supplies 5V, the switch receives 10V and 0V; when it supplies 0V, the switch receives 0V and 10V, meeting its operational voltage requirements.
The voltage conversion circuit is designed to convert the 5V control signal to 10V. When input1 is 5V, transistor Q3 turns on, Q5 turns off, and Q1 turns on, resulting in output1 being 0V. At the same time, Q4 turns off, Q6 turns on, and Q2 turns off, making output2 10V. Conversely, when input1 is 0V, Q3 turns off, Q5 turns on, and Q1 turns off, making output1 10V, while Q4 turns on, Q6 turns off, and Q2 turns on, resulting in output2 being 0V. This ensures the correct voltage is applied to the switch for proper operation.
For the RF switch circuit design, the idea is to use DC signals to control the on/off state of PIN diodes, allowing the RF signal to pass through the activated diode. By changing the control logic, different RF signals can be selected and routed accordingly.
The design process includes:
1. **Designing the DC control circuit**: The chosen diode is INFINEON BA592, which operates best at 5mA. A 10V control voltage is used, with resistor values of 10kΩ for R7, R8, R11, and R12.
2. **Designing the AC signal circuit**: With a center frequency of 63.6MHz, impedance matching is crucial. One RF signal is output while the other is matched to a 50Ω resistor. A 10nF coupling capacitor and an 18μH inductor are used to separate DC and AC signals.
3. **Basic modules and their connections**: Two types of modules are used. The 2x2 module allows two inputs to be routed to two outputs based on control logic. The 2x1 module routes two inputs to one output, with the other connected to a 50Ω resistor for matching.
4. **PCB design**: The final step involves designing the printed circuit board to ensure reliable and efficient signal routing and performance.
This RF switch design offers a more robust and cost-effective solution compared to traditional switch chips, especially in environments where reliability and ease of use are critical.
O.D114MM Hydraulic Dc Motors,O.D114MM Hydraulic Dc Motor,O.D114MM Dc Hydraulic Pump,O.D114MM Dc Hydraulic Pump Motor
Wuxi Jinle Automobile Motor Factory , https://www.wxjldj.com