About Circuit Envelope Simulation

This is a description of Circuit Envelope simulation, including when to use it, how to set it up, and the data it generates. Examples are provided to show how to use this simulation. Detailed information describes the parameters, theory of operation, and troubleshooting information.

Circuit Envelope simulation, simulates high-frequency amplifiers, mixers, oscillators, and subsystems that involve transient or modulated RF signals. You can simulate:

• Amplifier spectral regrowth and adjacent channel power leakage with digitally modulated RF signals at the input
• Oscillator turn-on transients and frequency output versus time in response to a transient control voltage
• PLL transient responses
• AGC and ALC transient responses
• Circuit effects on signals having transient amplitude, phase, or frequency modulation
• Amplifier harmonics in the time domain
• Subsystem analyses using modulation signals such as multilevel FSK, CDMA, or TDMA
• Efficient third-order-intercept (TOI) and higher-order intercept analyses of amplifiers and mixers
• Time-domain optimization of transient responses
• Intermodulation distortion (although the Harmonic Balance simulator, with the new Krylov option selected, may provide a faster solution in most cases)

Typical applications for the Circuit Envelope simulation include:

• Time Domain Data Extraction
  Selecting the desired harmonic spectral line it is possible to analyze:
  • Amplitude vs. Time
    Oscillator start up
    Pulsed RF response
    AGC transients
  • Phase vs. Time
    VCO instantaneous frequency, PLL lock time
  • Amplitude & phase vs. time
    Constellation plots
    EVM, BER
• Frequency Domain Data Extraction
  By applying FFT to the selected time-varying spectral line it is possible to analyze:
  • Adjacent channel power ratio (ACPR)
  • Noise power ratio (NPR)
  • Power added efficiency (PAE)
  • Reference frequency feedthrough in PLL
  • Higher order intermods (3rd, 5th, 7th, 9th)

In ADS, in the Envelope simulation controller is available in the Simulation-Envelope palette.

See the following topics for details on Circuit Envelope simulation:

• Using Circuit Envelope Simulation explains when to use Circuit Envelope simulation, describes the minimum setup requirements, and gives a brief explanation of the Circuit Envelope simulation process.
• Examples of Circuit Envelope Simulation is a detailed setup for calculating intermodulation distortion, using a Gilbert Cell mixer as the example. The location of the mixer example is also given.
• Limitation of Circuit Envelope Simulation explains the limitions of using Circuit Envelope simulation.
• Envelope Simulation Parameters provides details about the parameters available in ADS for the Envelope simulation controller.
• Theory of Operation for Circuit Envelope Simulation is an outline of the simulation process, with specific details of the Circuit Envelope simulator including a user-selected mode that can speed up lengthy cosimulations of Analog/RF circuits.
• Troubleshooting a Circuit Envelope Simulation offers suggestions on how to improve a simulation.