The Keysight PathWave Design 2021 suite of EDA tools focuses on 5G design, simulation and verification. For RF/microwave applications, the PathWave Advanced Design System (ADS) addresses three critical requirements for 5G product development, requirements not satisfactorily met by other EDA tools:
- Assembling and performing 3D electromagnetic (EM)-circuit co-simulation on multi-technology modules
- Simulating performance with modulated signals and verifying performance with 5G modulation standards
- Analyzing the stability of multi-device amplifiers under small- and large-signal operation
From 4G to 5G, operating frequencies have increased by a factor of 40, i.e., from the 700 to 2600 MHz bands to the 28 to 40 GHz bands. The density and complexity of system integration are increasing - adding phased array antennas, for example - and digital modulation has replaced analog. The implications of these changes for RF/microwave component designs are many:
Multi-technology Components – Design flows need to support the assembly and interconnect of multi-technology components - RFICs, MMICs, wafer-level packages, phased array antennas, laminates and PCBs - into dense, complex RF modules and subsystems. Design rule checking (DRC) and layout vs. schematic (LVS) for manufacturing sign-off must extend across the entire multi-technology structure.
3D EM Effects – EM effects at mmWave degrade circuit performance, increasing loss and coupling and shifting frequency. Circuit designers need to understand these 3D EM effects from packages and interconnects during design exploration, tuning and optimization, not just at the final verification of the completed design, when unexpected performance may force a redesign.
EVM Simulation – Digitally modulated RF signals require error vector magnitude (EVM) as the new figure of merit for circuit design and optimization. Traditional analog rules for 3G and 4G can lead to performance not meeting spec or over designing circuits, leading to greater power consumption.
Stability – Combining higher transistor gain, which is increased to offset high frequency losses at mmWave, with unwanted coupling from densely integrated circuit can lead to unstable amplifiers. Analyzing amplifier stability under nonlinear large-signal conditions is required to avoid unstable hardware.
Historic design flows are not adequate to ensure design success for 5G, automotive radar and other mmWave applications. Each component in a system cannot be designed stand-alone; they must be analyzed together, as an integrated system. From the transistor to the antenna far field, the EM, circuit and electrothermal analyses should be integrated across technology boundaries. It is not trivial to analyze ICs in packages with present design tools, and it is nearly impossible to analyze EM and real signals to understand the effects of modulated waveforms in a multi-technology 3D structure. Keysight developed PathWave ADS 2021 to address these difficulties, tapping its domain expertise in both measurement and simulation.
MULTI-TECHNOLOGY MODULE CO-SIMULATION
ADS 2021 is an open EDA platform based on the open access (OA) database architecture for the efficient assembly and routing of 3D integrated RF module structures:
- RFIC and chip-scale antenna layouts based on OA (e.g., Virtuoso, EMPro)
- PCB and laminate layouts based on ODB++ (e.g., Allegro, Expedition, Zuken)
- ADS native MMIC and RF layouts
A unique assembly technology called SmartMount automatically handles different units (e.g., µm and nm for ICs; mm, mils and inches for PCBs and laminates), orientation (e.g., top/bottom mount, flip chip) and adjacent technology stack-up definitions. After assembly, ADS layout behaves as both a package and IC layout tool: building hierarchical sub-structures like an IC tool and “avoidance route” 3D interconnects like a package tool. This makes building and assembling packages straightforward, as well as accounting for package effects on the IC’s performance (see Figure 1). Another unique capability called module-level DRC and LVS ensures the correctness of the multi-technology module for building the hardware.
RFPro in ADS 2021 is an automated 3D EM-circuit co-simulation capability, enabling easy analysis of the EM performance of any portion of a design, without layout cookie cutting and tedious setup of ports, ground references and 3D EM simulation parameters. The 3D EM results are automatically combined with the circuit simulation to immediately analyze the EM effects of packaging, interconnect and coupling on circuit performance. This enables the circuit designer to perform 3D EM analysis and EM-circuit co-simulation seamlessly, without manual setup errors or waiting for scarce experts to perform the EM analysis. The result is orders-of-magnitude faster EM-circuit co-simulation, from weeks and months to seconds and minutes.
CIRCUIT EVM SIMULATION
5G, automotive radar, Wi-Fi 6E and IoT - almost all wireless applications - employ digitally modulated signals, and EVM is the common figure of merit for measuring the linearity performance of a circuit or system with digital modulation. Particularly with increasing signal bandwidth and modulation density, traditional rules of thumb like P1dB or IP3 as indicators of linearity are obsolete.
ADS 2021 has the first circuit EVM simulation, using Keysight’s fast EVM measurement and compact test signal algorithms (see Figure 2). The capability enables designers to tune and optimize a design for EVM, removing inaccurate rules of thumb and guesswork when designing components or systems with digitally modulated signals.
ADS 2021 also offers Keysight’s instrument grade 5G sources and demodulation algorithms in a preconfigured 5G virtual test bench (VTB), which eliminates the complicated setup for 5G compliance tests. VTBs provide accurate compliance verification for RF component designs before the hardware is built, establishing confidence early in the development cycle.
With applications well into mmWave frequencies - 5G and automotive radar at 40 and 77 GHz, respectively - transistor gains have increased to offset mmWave losses. However, high gain with dense integration increase the risk of unstable amplifiers from unintended coupling. ADS 2021 provides a unique amplifier stability analysis called the Winslow technique, a unified simulation replacing 28 separate techniques (see Figure 3). This single, all-encompassing stability analysis assesses amplifier stability under both small- and large-signal operating regions.
Pathwave ADS 2021 enables the design, simulation and verification of RFIC, MMIC, RF module and RF PCB components and subsystems for 5G and other wireless applications, with capabilities not available in competing EDA tools. Using ADS 2021 for design, a company can have more confidence in the capability of its design process and achieve early design wins.
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