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SPICE up your life: Comparing SPICE simulators

25 Feb 2015  | Rajan Bedi

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I am a great believer of design re-use and both Hyperlynx Analog and PSpice allow the design drawn for circuit simulation to be re-used as the schematic for PCB floor-planning, layout, and product design. In the real world, a single stage of entry avoids unnecessary duplication and errors, helping space-electronic products get to market faster and be developed to cost and schedule. Both LTSpice and Hyperlynx Analog support hierarchical simulation using symbols while PSpice prefers a flat design as it tends to repeat references throughout a hierarchy.

Hyperlynx Analog allows users to back-annotate and import SPICE or S-parameter trace data from the routing to account for its parasitic effects. Mentor's PCB flow also permits the prediction of EMI, thermal, and power-integrity effects, and if you are producing spacecraft avionics, these tools are essential to ensure your hardware is delivered right-first-time.

Unlike the other tools in this comparison, Hyperlynx Analog allows me to simulate low-frequency, DC-DC converters, as well as high-speed, mixed-signal circuits where I can import third-party S-parameter component models, or extract the S-parameters of a complete network to account for layout effects. For this comparison, I used the Eldo simulator within Hyperlynx Analog. The three tools permit analogue circuits and logic to be co-simulated which is useful for digital control of voltage regulators and ADCs/DACs.

The quality of simulation models provided by suppliers of power microelectronics varies immensely and I encourage vendors of DC-DC converters to get in touch if they need help to produce models that are fit for the space industry, and compatible with the EDA tools used by manufacturers of satellite sub-systems and spacecraft.

A word of caution: simulation does not replace breadboarding prior to a production build! Modelling allows you to predict the behaviour of your regulator and debug flaws quickly and at low cost, permits what-if analyses without the fear of blowing anything or anyone up, lets you understand how a design reacts to faults such as a short-circuit, and simulates test measurements if you do not have access to the relevant equipment. A working SPICE model doesn't necessarily mean your prototype hardware will work first time: if you 'wire' your model as you would in a lab accounting for ohmic losses, leakages, and parasitics, the predicted performance should correlate with that measured from your Engineering Model. In the real world of product development, simulation MUST be supplemented by measurement of loop stability from your hardware to minimise risk. Component parasitics, temperature, and PCB layout all affect control-loop stability, and no experienced designer would rely solely on modelling to predict critical performance. Measurement should be performed on the prototype, qualification, and flight builds.

To help designers predict loop gain and phase margin, several vendors provide free modelling software that uses proprietary simulation models specific to their parts, e.g. Linear Technology's PowerCAD and Analog Devices' ADIsimPower. SIMPLIS, PSIM, and Power 4-5-6 are also very useful and quicker than SPICE-based modelling, and top-down tools such as Simulink use behavioural models to predict the stability of the feedback-control loop and I really like the speed of this approach.

Space-electronics companies invest a lot in EDA software and many do not understand the capability or potential of such tools to get their products to market right-first-time, delivered to cost and schedule. In many instances, businesses use simulation software from one supplier and schematic entry and PCB layout software from another, unnecessarily duplicating design entry, buying multiple licences, and having to learn two flows. Please don't make this expensive mistake!

About the author
Rajan Bedi is currently CEO of Spacechips. Rajan worked at Astrium (now Airbus) for twelve years developing and researching space-grade electronics for telecommunication, navigation, Earth-observation and science missions. As Head of the Mixed-Signal Design Group, Rajan's team developed the hardware for the award-winning, channelising payload currently operating on-board the Alphasat telecommunication satellite.

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