In RF integrated circuit design, what is RF circuit simulation?

Figure 1. RFIC design requires balancing multiple, often conflicting, objectives.

Compared to digital ICs, RFICs are more sensitive to noise, crosstalk, and parasitic effects due to their high-frequency and high-precision requirements. RFIC specifications impose stricter demands regarding speed, frequency range, functionality, performance, linearity, precision, power consumption, noise, cost, and radiated emissions.

While meeting customer demands for higher speeds, higher frequency bands, expanded functionality, and superior performance, designers must skillfully balance these often-conflicting criteria.

Decisions and assumptions regarding this balance begin at the schematic capture stage—the first step following the determination of specifications and architectural choices. Identifying design issues and optimizing trade-offs at this early stage is far faster and less costly than doing so later in the process. This is why the concept of “shifting left” has become so critical in the semiconductor industry.

By running RF circuit simulations directly on the schematic, designers can rapidly explore various options and assumptions, and easily modify the design to achieve optimal trade-offs. Designers can iteratively:

·Adjust the values ​​of passive components (resistors, capacitors, and inductors)
·Experiment with bias thresholds for active components such as transistors
·Quickly re-run simulations
·Identify emerging issues
·Resolve these issues by modifying the design or design parameters

Figure 2. RF circuit simulation types

Some common RF circuit simulations are listed below:

·S-parameter simulation: These enable designers to maximize forward gain (S21), minimize return loss (S11 and S22) to achieve good impedance matching, and ensure high isolation (S12).
·Linearity simulation: For RF power amplifiers and mixers, linearity simulations help maximize metrics such as the 1-dB compression point and the third-order intercept point (IP3).
·Noise simulation: For low-noise amplifiers and other sensitive receivers, these simulations help minimize the noise figure.
·Power simulation: For power amplifiers, simulations help maximize power-added efficiency or overall efficiency while minimizing power consumption across individual modules.
·Stability simulation: Designers can verify unconditional stability over a wide frequency range by simulating factors such as the K-factor and stability circles.
·Bandwidth simulation: Designers can verify the operating bandwidth for various metrics (such as flat gain or low return loss) within a specific frequency range.
·Modulation simulation: Designers can simulate complex modulation schemes used in real-world 5G, 6G, Wi-Fi 7, and other signals to explore their impact on metrics such as Error Vector Magnitude (EVM) and Adjacent Channel Power Ratio (ACPR).