ADS system simulation model helps development of Envelope Tracking systems
The ET System Simulation model, jointly developed by OpenET members Nujira and the University of Firenze, aids system optimization by making it easier for designers to identify sources of noise and distortion and to make the necessary design tradeoffs.
The System Simulation model, which has been developed using Agilent’s Advanced Design System (ADS), provides a framework to model a complete handset ET system, and incorporates a High Dynamic Range (HDR) RF Power Amplifier model developed by Nujira.
System simulation capability is particularly important in Frequency Division Duplex (FDD) systems, such as the 4G LTE standard, where the transmit and receive paths are operating simultaneously. Multiple noise and distortion mechanisms in the transmit path can feed into the receive path, and can result in reduced receiver sensitivity.
Envelope Tracking introduces new digital and analog paths, which can contribute to the system noise budget. With so many interactions and co-dependencies to consider, comprehensive system simulation is the only viable way for the designer to make the necessary system tradeoffs. However, PA models based on captured data have typically suffered a ‘noise floor’ of around -90 dB, which masks many of the other system effects.
The OpenET Alliance’s High Dynamic Range (HDR) PA simulation model overcomes this problem. Instead of interpolating between measured data points, the HDR PA model uses an algorithmic representation of the PA behavior to generate a continuously variable output, eliminating measurement noise and quantization errors. This mathematical modeling approach enables a simulation environment with almost 150 dB of dynamic range.
"For a system designer developing Envelope Tracking transceivers, a high dynamic range system simulation environment is essential for system designers to be able to ‘see the wood for the trees’ and identify and optimize the multiple sources of noise and distortion," said Steven Baker, Technical Director of the OpenET Alliance. "The HDR PA model is another significant milestone for the mainstream adoption of ET, removing a crucial hurdle in the process of developing optimizing systems operating in ET mode."
The HDR PA model can be parameterized with surfaces of gain, phase and efficiency extracted from real device measurements. The model can also be run with phase distortion (AM/PM) disabled, allowing the system designer to model a ‘perfect’ memoryless PA, giving full visibility of the contributions from, and interactions between, the other system elements.
The HDR simulation model is released to members of the OpenET Alliance as an ADS Design Kit component, linking with the OpenET Alliance’s complete ADS ET System Simulation Model.
The model is suitable for use by chipset designers, PA vendors, filter manufacturers and handset OEMs, and is being released to members of the OpenET Alliance for download from www.open-et.org