VSWR
Joined: 07 Feb 2002
Posts: 767
Helped: 72
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 09 Apr 2009 19:01 re line envelope |
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From
http://edocs.soco.agilent.com/display/ads2009/About+Circuit+Envelope+Simulation:
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.
When to Use Circuit Envelope Simulation
Circuit Envelope is highly efficient in analyzing circuits with digitally modulated signals, because the transient simulation takes place only around the carrier and its harmonics. In addition, its calculations are not made where the spectrum is empty.
•It is faster than Harmonic Balance, assuming most of the frequency spectrum is empty.
•It compromises neither in signal complexity, unlike Harmonic Balance or Shooting Method, nor in component accuracy, unlike Spice, Shooting Method, or DSP.
•It adds physical analog/RF performance to DSP/system simulation with real-time co-simulation with ADS Ptolemy.
•It is integrated in same design environment as RF, Spice, DSP, electromagnetic, instrument links, and physical design tools.
Circuit Envelope provides these advantages over Harmonic Balance:
•In Harmonic Balance, if you add nodes or more spectral frequencies, the RAM and CPU requirements increase geometrically. The Krylov solver improves this, but it is still a limitation of Harmonic Balance because the signals are inherently periodic.
•Conversely the penalty for more spectral density in Circuit Envelope is linear: just add more time points by increasing tstop. The longer you simulate, the finer your resolution bandwidth.
•Doing a large number of simple one-tone HB simulations is effectively faster and less RAM intensive than one huge HB simulation.
•With a circuit envelope simulation the amplitude and phase at each spectral frequency can vary with time, so the signal representing the harmonic is no longer limited to a constant, as it is with harmonic balance.
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