Circuit Envelope
RF Simulation Engine Comparison
| Simulation Engine | Domain | Primary Use Case | Cannot Simulate |
|---|---|---|---|
| S-Parameters (Linear) | Frequency | Small-signal gain, matching, filters | Compression, harmonics, distortion |
| Harmonic Balance (HB) | Frequency | P1dB, IP3, steady-state tones | Digital modulation, random data |
| Transient (SPICE) | Time | Oscillator start-up, step response | High-frequency carriers over long durations |
| Circuit Envelope | Mixed (Freq + Time) | EVM, ACLR, digitally modulated signals | Cannot be used without valid nonlinear models |
v(t) = A(t) · cos[2πfct + Φ(t)]
Where fc is the fast carrier frequency. Circuit Envelope ignores the repetitive fc completely and only calculates A(t) [amplitude modulation] and Φ(t) [phase modulation] at each time step.
Simulation Speed Advantage:
If fc = 28 GHz and the modulation bandwidth is 100 MHz, standard SPICE requires time steps < 5 picoseconds. Circuit Envelope only requires time steps of ~5 nanoseconds (driven by the modulation bandwidth), making it roughly 1000 times faster.
Frequently Asked Questions
How does it differ from Harmonic Balance?
Harmonic Balance is a purely steady-state, frequency-domain simulator. It assumes the input signal is a continuous, never-changing sine wave. It is perfect for calculating IP3 using two steady tones. But a real 5G signal is random data; it changes constantly. Circuit Envelope runs a rapid Harmonic Balance simulation at every single time-step to capture the dynamic, changing nature of the signal.
What inputs are required for Circuit Envelope?
You need a non-linear model of your active devices (e.g., an X-parameter model or a compact model like Angelov/BSIM) and an IQ data file. The IQ data file contains the digital baseband symbols (In-phase and Quadrature) that represent the actual modulated data stream (like QAM or OFDM) that you want to push through the amplifier.
Can it simulate Envelope Tracking (ET)?
Yes. Because it solves both the high-frequency RF path and the slow-moving baseband path simultaneously, Circuit Envelope is the only engine capable of simulating Envelope Tracking power supplies. It can simulate the baseband processor generating the dynamic drain voltage, delay that voltage appropriately, and apply it to the PA's drain while the RF envelope hits the gate.