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What is an RF Front End (RFFE)?

By Cyprien Rusu 18 August 2019

In current mobile devices, there is a sophisticated circuitry that is responsible for converting information from the near-zero frequency baseband signals used to convey information and data to radio-signals that can be received or transmitted over the air.

This is basically what the RF Front End does… which is a HUGE job

RF Front End
The RF Front End (RFEE) needs to process the right data at the right time with the right information and send it with the right band at the right power level. In a modern smartphone, there are multiple antennas for transmit and receive signals.

There could be 6 or more Antennas (3G, 4G, 5G, WIFI, GPS…), depending on the technology!

For each Antenna, there must be a path either for transmit or receive that will get the signal from the antenna to the model.

Those paths are called RF Signal Pads or RF Chains. As more Antennas are added to the device you need more RF Chains. Each RF Chains needs a series of components that process the signal and all of those components as well as the interaction of those components with Antennas and with the modem need to be understood in details.

Looking forward to 5G that will bring more and more Antennas on the device, it is important for RFFE to evolve!

How does a RF Front End works in a Traditional Radio Receiver?

Let’s look a bit closer at the RF Front End of a Radio Receiver Circuit to see what it does:

The RF Front end is the generic name for all the circuitry between a receiver Antenna input up to the Mixer Stage.

For most architectures, the RF Front End consists of:

  • An RF Filter (which is actually a band-pass filter) receives the Electromagnetic wave from the Antenna. His role is to remove the image frequency and to prevent strong out-of-band signals from saturating the input stages.
  • An RF amplifier which is used to amplify weak signals without adding noise
  • A local oscillator which generates a stable radio frequency signal close to the input signal
  • A Mixer which produces a signal at a certain wanted frequency by “Mixing” the E-M Wave signal from the Antenna with the Local Oscillator Signal.

Note 1: The image frequency is an unwanted input frequency equal to the station frequency plus or minus the intermediate frequency

Note 2: The Mixer is a nonlinear electrical circuit that creates new frequencies from two signals applied to it. Those two signals produced are at the sum and difference of the two input signals. Generally, only one of those resulting signals is really wanted, the other is just not used.

How about RF Front Ends in cell phones?

In cell phones, the frequency produced by the Mixer (also called intermediate frequency) is digitized, sampled and converted to a binary digital form and the rest of the processing is done by digital filters which are smaller, use less power and can have more selectivity.

What are the main challenges of designing such RF Front Ends for cell phones?

Each RF Chains needs a series of components that process the signal.

In cell phones and mobile devices, there are many challenges due to the number of Antennas:

  • The various signals that must not interfere with each other
  • Choosing or Designing the proper components for each part of the RF Chains

Designers need to consider how to design systems that will sustain the architecture of the communication of the future!

Can Simulation be used to solve such engineering problems?

Of course! Actually, simulation is the only reliable way to solve the major problems that will allow us to generate signals at higher frequencies within devices that can go into our pocket! If you think about it, the system architecture for 5G RF Front Ends will be extremely complex and require to fit 100+ RF Filters into a smartphone. Designer will need to think about the cost, the power efficiency, the available space, and the ability to manufacture all of that in large quantities to meet the fast-growing global demand. Innovative RF filter design solutions will be required to simplify the design process and reduce the size of filters while at the same time improving their performance.

Currently, OnScale is the only Simulation software capable to simulate the newest types of RF Filters in full 3D (SAW Filters, BAW Filters, SMR Resonators…) to calculate directly and reliably the performance parameters such as the Q factor needed to understand fully the behavior of those complex systems.


SAW Resonator

OnScale also uses the power of the cloud to run 1000s of simulations at the same time and calculate the full design space solution of those new generation RF Devices. With OnScale, designers and engineers have been able to optimize RF Filters using genetic algorithm or by training AI Machine learning algorithms.

Want to know more about how to simulate all that?

Check our Simulation Guides for RF Filters!

You can also check our Simulation-Driven Optimization of 5G RF MEMS Filters White Paper!


Cyprien Rusu
Cyprien Rusu

Cyprien Rusu is our Director of Engineering for Asia at OnScale. He has a extensive background in FEM, Technical Marketing, Sales and Support. Cyprien recieved his MS in Civil Engineering from Tsinghua University. At OnScale he is a trusted advisor for our client base in Asia, while creating and providing OnScale training.

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