What is the difference between vector signal and RF signal source?

The signal source can provide accurate and highly stable test signals for various component and system test applications. The signal generator adds an accurate modulation function, which can help simulate the system signal and perform receiver performance testing. Both the vector signal and the RF signal source can be used as the test signal source. Below we have their own characteristics under analysis.
What is the difference between vector signal and RF signal source?
1. Introduction to Vector Signal Source
The vector signal generator appeared in the 1980s, and used the intermediate frequency vector modulation method combined with the radio frequency down conversion method to generate the vector modulation signal. The principle is to use a frequency synthesis unit to generate a continuously variable microwave local oscillator signal and a fixed frequency intermediate frequency signal. The intermediate frequency signal and the baseband signal enter the vector modulator to generate an intermediate frequency vector modulated signal with a fixed carrier frequency (the carrier frequency is the frequency of the point frequency signal). signal. The radio frequency signal contains the same baseband information as the intermediate frequency vector modulation signal. The RF signal is then signal-conditioned and modulated by the signal conditioning unit, and then sent to the output port for output.

Vector signal generator frequency synthesis sub-unit, signal conditioning sub-unit, analog modulation system and other aspects are the same as ordinary signal generator. The difference between the vector signal generator and the ordinary signal generator is the vector modulation unit and the baseband signal generation unit.

Like analog modulation, digital modulation also has three basic methods, namely amplitude modulation, phase modulation and frequency modulation. A vector modulator usually contains four functional units: the local oscillator 90 ° phase-shifting power division unit converts the input RF signal into two orthogonal RF signals; the two mixer units convert the baseband in-phase signal and the quadrature signal Multiply with the corresponding RF signal respectively; the power synthesis unit sums the two signals after multiplication and outputs. Generally, all input and output ports are internally terminated with a 50Ω load and adopt a differential signal driving method to reduce the return loss of the port and improve the performance of the vector modulator.

The baseband signal generating unit is used to generate the required digitally modulated baseband signal, and the waveform provided by the user can also be downloaded to the waveform memory for generating a user-defined format. The baseband signal generator usually consists of a burst processor, data generator, symbol generator, finite impulse response (FIR) filter, digital resampler, DAC, and reconstruction filter.

2. Introduction of RF signal source
Modern frequency synthesis technology often uses an indirect synthesis method to connect the frequency of the main vibration source and the frequency of the reference frequency source through a phase-locked loop. It requires less hardware equipment, high reliability, and a wide frequency range. Its core is a phase-locked loop, and the RF signal source is a relatively broad-spectrum concept. Generally speaking, any signal source that can generate an RF signal can ride the RF signal source. Current vector signal sources are mostly in the RF band, so they are also called vector RF signal sources.

Third, the difference between the two signals
1. The pure radio frequency signal source is only used to generate analog radio frequency single frequency signals, and is generally not used to generate modulated signals, especially digital modulated signals. This type of signal source generally has a wider frequency band and a larger power dynamic range.

2. The vector signal source is mainly used to generate vector signals, that is, commonly used modulation signals in digital communication, such as l / Q modulation: ASK, FSK, MSK, PSK, QAM, customized I / Q, 3GPPLTE FDD and TDD, 3GPPFDD / HSPA / HSPA +, GSM / EDGE / EDGE evolution, TD-SCDMA, WiMAX? And other standards. For the vector signal source, due to its internal band modulator, the frequency is generally not too high (about 6GHz). The corresponding index of its modulator (such as the built-in baseband signal bandwidth) and the number of signal channels is an important index.

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