Waveform time domain circuit simulator
This software can be used in the design of circuits, in which the conventional time domain and / or the harmonic balance based simulators are inadequate. Circuits and situations that would greatly benefit from the application of this software have some, or all, of the following characteristics:
- complex, externally defined voltage and / or current source driving waveforms
- signals large enough to cause strongly non-linear operation of the active devices
- the circuit has an inherently and strongly non-linear electrical response
- the circuit consists of a mixture of microwave passive elements, defined by S parameter data and non-linear active devices
- "transient" phenomenon are of interest, such as the start up of unintentional oscillations, or, the phase shift, as a function of time, in a pulsed microwave circuit
The Waveform simulator can be used to predict
- whether an amplifier, or, other such circuit will unintentionally oscillate, without requiring the user to inject any "oscillation start up pulses"
- the behaviour of a VCO, with slow and fast variations, in the control voltage (no predictions of phase noise)
- the response of a transient overload protection circuit
- the level of the harmonics generated in a linear amplifier, when the amplifier is driven by a high level input signal
- the interactions (particularly reflected signals) between MMICs, connected through the use of transmission lines
- the operation of ultra wide band (UWB) circuits, as used in UWB RADAR and other systems
- the phase shift added to a single frequency input signal, as a function of time, in a pulsed RF circuit (causing " time varying beam skew" when such circuits are used in a phased array RADAR system), resulting from dispersive effects in the PHEMT. For example, the circuit supply voltage may be pulsed ON for 1 uSec, during which time the circuit functions as a power amplifier, operating at around 10 GHz, after which the power is turned OFF
Waveform will predict the signals in non-linear circuits
- a Step Recovery Diode (SRD) based circuit for impulse generation
- a Non Linear Transmission Line (NLTL) based circuit
- a Schottky Barrier Diode (SBD) based signal sampling circuit
Waveform can use complex, base-band, driving signals
- a 10 GBit/sec Non-Return-to-Zero (NRZ) Pseudo Random Bit Sequence (PRBS)... as encountered in optical communications modules and circuits
- a very wide bandwidth noise or pseudo-noise signal (such as WCDMA)
- high bit rate, parallel data bus signals. As an example, in an 8 bit wide, 1 GBit/sec, data bus, the complex electrical characteristics of the 8 coupled microstrip data tracks could be defined through the use of an electromagnetic simulator, as a 16 port S parameter data set
Waveform can predict the response of a circuit:
- in an electrically noisy environment
- to signals picked up from a nearby, high power, RADAR system
- to impulses picked up from a nearby UWB RADAR system
- to signals picked up from a nearby, high power, electronic warfare system
- to an electromagnetic pulse (EMP) from a nuclear explosion, or, other such powerful electromagnetic source
The Impulse software on its own can be used to visualise the response of a passive element, or, circuit section in the time domain. If the visualisation indicates that part of the response appears to occur before time t=0, then the " non-causal" or " unphysical" response needs to be corrected, before the data is used in any simulation. The cause of such an " unphysical" response could result from the over de-embedding of measurement data, or, inaccuracies in the closed form mathematical equations, used to predict the real and imaginary parts of the circuit response, as a function of frequency.
The WaveMaker linear microwave circuit simulator
The WaveMaker linear microwave circuit simulation software, is used to predict the S parameter characteristics of a linear microwave circuit. The circuit can consist of the following elements:
- RLC ideal lumped components
- microstrip lines and discontinuities
- stripline elements
- elements defined by their S parameter data
The circuit description can be defined through the use of a text editor, to define the netlist, or, through the use of the in-built schematic capture capabilities of the software.
The predicted circuit response can be displayed on a rectangular graph, in Smith chart form (for Snn) or in tabular format, and / or can be exported as a Touchstone format S parameter date file.
The software supports the optimisation of circuit element parameters, to cause the overall circuit or sub-circuit response to more closely match the specified goals. The optimisation approaches supported include both random and gradient types. This feature is also used to derive the values for the circuit element parameters from network analyser measurements on the circuit.
Changes can be made to the circuit element values or the circuit topology and the new circuit response can be superimposed on the old circuit response, to get a clear idea of the effect of any changes made.
Through the use of the in-built Fast Fourier Transform, the user can visualise the waveform at the output of a linear network, when that network is subjected to a user-defined, input driving waveform.
The Impulse software
- S or Y parameters defined in a data file using the well-known Touchstone format.
- First frequency point need not be zero: if it is less than 1.0% of the second frequency, the software will assume this to be the zero frequency entry.
- The interval between all the adjacent frequency points (with the first point assumed to be at zero Hz) must be the same and must equal the value of the second frequency point.
- Data for structures with from one to 19 ports may be used.
- Any of the S or Y parameters may exhibit gain (ie. Smn greater than 1.0).
Overview of Waveform specifications
Elements supported include:
- Voltage Controlled Voltage Source with optional use of delay
- Voltage Controlled Current Source with optional use of delay
- d.c. voltage and current sources
- sine wave voltage and current sources
- external waveform controlled voltage and current sources
- Import of 1 to 19 port S or Y parameter data blocks
- Standard SPICE compatible diode model
- TOM, TOM2, TOM3, Cobra and EEHEMT1 GaAs FET models
The Waveform software
- will calculate equivalent circuit model (including noise sources) values for each active device at quiescent bias point.
- will display bias voltages and currents, on the circuit schematic.
- will generate a data base containing the predicted voltages, at each node in the circuit.
- can be used to superimpose bias plane trajectory on FET IV characteristics.