Model a Mixer Chain

RF Blockset™ Equivalent Baseband software uses a baseband equivalent model to simulate RF components in the time domain. The blockset only models a band of frequencies around the carrier frequency of each component; the frequency band is determined by the following parameters of the corresponding Input Port block:

• Reciprocal of the Sample time (s)

• Center frequency (Hz)

When a mixer is present in a physical subsystem, it shifts the carrier frequency of the signal. This shift affects the frequencies that are used to create baseband equivalent model.

To illustrate how the mixer works, consider a typical RF mixer chain that consists of the following components:

• Direct Quadrature Upconverter

• High-Power Amplifier

• Channel

• Low-Noise Amplifier

• Downconverting Mixer

• IF Filter

• Direct Quadrature Downconverter

The following diagram shows these components and the band of frequencies that are simulated for each component. The signals at the input and output of the cascade are baseband complex. For the cascade, the diagram shows the real passband frequencies that are used to create the baseband-equivalent model, which is centered at zero. For a detailed explanation of how to use the blockset to model quadrature mixers, see Quadrature Mixers.