Working principle, composition structure and application of RF signal source

What are the specific parts of the RF signal source? The following editor will take you to understand what modules the RF signal source is composed of after being disassembled.

The specific components of the RF signal source are mainly the following parts: AC-DC power board, digital board, RF board, OCXO board, DC-DC power board, keyboard board, frequency multiplier board, ATT board, IQ board, LCD board. I have divided them in detail above. If some low-frequency sources do not have frequency multiplier boards and ATT boards, or if the frequency is not high, the frequency multiplier function can be integrated on the RF board.

AC-DC Power Supply Board

The main function is to convert the AC voltage of the mains into DC power, and then supply power to the DC-DC power supply board.

DC-DC Power Supply Board

This module is used to reduce the output voltage of the AC-DC module to a certain value, and then convert it to meet the power supply (voltage and current) required for the normal operation of each functional unit. For example, the power supply of the fan and other boards (such as the RF board and the frequency multiplier board) are all provided by the DC-DC power supply board.

Digital motherboard

The digital motherboard stores the product's software information. For example, the software we upgrade and the product's serial number and hardware version are all managed by the digital motherboard.

Keyboard and LCD panel

Provide key and display functions. Debugging is mainly divided into the following steps: power supply, clock, program download, digital circuit function, power supply debugging to ensure the most basic conditions for the normal operation of each power supply of the circuit, and then debug the digital circuit. To debug the digital circuit, first ensure the correctness of the clock and provide power for the digital chip, then load the program code, and then see the performance of the digital circuit, test whether its display, keyboard, and external interface functions are normal.

RF Board

The most important part of the RF board is the processor, which is responsible for tasks such as human-machine interaction, data communication, system data calibration, system control, data call storage, etc. In order to quickly respond to the frequency or amplitude switching of the whole machine, complex control and calculation, the control of the RF circuit is realized by the RF FPGA.

The RF circuit of the RF signal source is divided into four parts: frequency synthesis, modulation, amplitude adjustment, and LF. Finally, the entire system is powered by an AC-DC power supply. The frequency synthesis part includes a synchronization circuit with a 10M TCXO as the core, a DDS frequency synthesis circuit, a local oscillator circuit, a mixing frequency synthesis circuit, a pulse modulation circuit, an ALC circuit, an AM modulation circuit, an amplifier circuit, and a step attenuator circuit.

OCXO board and TCXO circuit

The 10MHz (TCXO) in the clock circuit is the frequency reference of the RF frequency of the entire RF board, and is also the working clock of the digital circuit (FPGA), which is realized by a crystal oscillator. When an external reference or OCXO is inserted, the reference PLL works and locks. The control signal of the switch selection circuit is controlled by the monitoring circuit of the OCXO and the external reference. The clock external reference and OCXO are both to provide a more accurate reference synchronization clock for the TCXO through the PLL. The principle is that the system clock TCXO can only synchronize one of the OCXO or the external input reference signal through the PLL. When there is no external reference, the TCXO provides a reference; when there is an external reference signal, the synchronization circuit automatically selects the external signal as the reference.

Frequency doubling board

The low-frequency signal comes from the RF output of the RF board and passes directly through the multiplier board. The high-frequency part generates a higher-order frequency signal through multiple multiplication. After filtering, ALC control is performed and output to the ATT board.

ATT Board

The ATT board is mainly an attenuator, PA and switch related board, providing a combination of different amplitude outputs.

I/Q Board

The I/Q board is mainly responsible for I/Q modulation, that is, two orthogonal signals (carriers with the same frequency and a phase difference of 90°, generally represented by Sin and Cos) are respectively modulated with I (In-Phase, in-phase component) and Q (Quadrature Phase, orthogonal component) signals and then transmitted together, thereby improving spectrum utilization. I/Q modulation can select internal sources or pass-through.