μWaveRiders: Simulating Mixed-Signal RF Systems with AWR VSS Software

24 Feb 2021 • 4 minute read

Team RF The Team RF "μWaveRiders" blog series debuts as a showcase for Cadence AWR RF products. Monthly topics will vary between Cadence AWR Design Environment release highlights, feature videos, Cadence Academic Network news (now includes the former AWR University Program), as well as software tips, tricks, customization, and feature spotlights. To receive notifications about new blogs in this series, click Subscribe Now and submit your email ID in the Subscriptions box.

Depending on the application, the term system conjures up different interpretations. System on chip (SoC), embedded system, and power management system are just a few examples in electronics where the term system has meaning. The Cadence AWR Design Environment platform includes the AWR Visual System Simulator (VSS) communications and radar systems design software for the design of systems particular to the RF community. AWR VSS software allows analysis capability for RF systems including communications link, radar, and test instrumentation.

RF Communications Systems

In an RF communications system, the main components that comprise the link are the transmitter, the receiver, and the channel. Figure 1 shows a high-level block diagram of an RF communications system.

RF Communications System

Figure 1. RF Communications System

Depending on the application, either digital or analog data are converted to RF in the transmitter. The transmitter then sends the RF signals through a channel to the receiver. The channel medium can be either over-the-air, wired cable, or fiber-optic cable. The receiver converts the RF channel signal to the reconstructed digital or analog data signals. The goal is faithful reproduction and receipt of the transmitted data despite the presence of noise, distortion, and interfering spurious signals anywhere along the communications system link.

The difficulty in analyzing an RF communications system stems from the divergent signal types that comprise the overall link. Figure 2 shows a subset of the RF communications system, the transmitter.

Figure 2. Transmitter Block Diagram

Within this single transmitter block, a system designer must contend with digital, analog, and RF signals. In the digital realm, a system designer would typically experiment with various error correction algorithms, techniques for mapping symbols to the IQ constellation, and pulse shaping to reduce inter-symbol interference. The analog design portion entails a digital-to-analog converter, an IQ modulator, and an intermediate frequency (IF) local oscillator as well as any IF amplifiers, filters, etc. Many communications systems operate in the RF, microwave, or even optical spectrum. The RF blocks include the carrier oscillator, upconverter mixer, and power amplifier. Depending on the system, an antenna design may be included. Anywhere along this link, disturbances in the form of both noise and distortion may impair the signal.

Radar Systems

Radar is another example of an RF system. A typical radar block diagram also consists of digital, analog, and RF elements as shown in Figure 3.

Radar Block Diagram

Figure 3. Radar Block Diagram

Depending on the type of radar system, waveform generation consists of digital signal processing, digital-to-analog conversion, and analog signal analysis for the transmit section. Pulse compression, chirp, and pulse generation algorithm development and analysis are examples of waveform generation requirements. In the receive section, the detection block also consists of analog and digital signal analysis and algorithm development. In both the transmit and receive sections, RF analysis is required for the up/down converters, power amplifier, and low noise amplifier.

AWR VSS Software Analysis of RF Communications Systems

AWR VSS software is a comprehensive tool that allows analysis of all aspects of the RF communications system: digital, analog, RF/microwave and over-the-air channel transmission. All disciplines of the RF link can be combined in a single design to allow overall analysis and design optimization of the entire mixed-signal link including:

Digital design using fixed point data
Algorithm development for digital modulation that conforms to either a generic format such as QAM, OFDM, and QPSK, or libraries of specific communications standards such as 5G NR, LTE, and GSM
Analog and RF design using CW signals as the stimulus for the analysis of gain, output power, noise figure, inter-modulation distortion, harmonic distortion, etc. in order to determine sufficient link budget
Complete end-to-end system development with digital modulation as the stimulus to measure metrics such as EVM, BER, and ACLR

The elements used in RF system projects can consist of behavior models, vendor-supplied data files, linear or nonlinear circuit schematics, or electromagnetic (EM) structures.

This blog highlights the types of RF systems that AWR VSS software aids in analyzing. Future blogs in this series will include details on time-domain vs. frequency-domain analysis, digital signal processing, and RF budget analysis capabilities within AWR VSS software. For more information on Cadence AWR products, visit the Cadence website.

By: Brian Avenell
Sr. Principal Product Engineer
Cadence AWR R&D - U.S.

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