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EDA on the iPad

EDA on the iPad
by Daniel Payne on 04-02-2012 at 1:16 pm

I started a forum discussion about running Schematic Capture and SPICE on an iPad back in January, since then I bought an iPad 3rd generation and tried out that app.

It was easy to visit the App store, find the Spicy Schematic Capture app, download and start learning how to use their schematic and SPICE circuit simulator.

To get started quickly there is a library of demo circuits that you can view and simulate. Or, you can visit their YouTube page and see how it works.

The tool is focused more on PCB design and simulation, or placing small parts, Resistors, Capacitors and sources.

One library design that caught my attention was for an SRAM cell:

The netlist looks just fine for SPICE syntax and you can email your netlist from the iPad:

[CODE]******************************************
* Netlist and simulation file
* Generated by: SPICY Schematics (ischematics.com)
* File: Sram(2)
******************************************
.GLOBAL vdd!

M0 N_Q N_QB 0 0 NFET
M1 N_QB N_Q 0 0 NFET
M2 N_QB N_Q vdd! vdd! PFET
M3 N_Q N_QB vdd! vdd! PFET
M4 N_BL N_WL N_Q UN6 NFET
M5 N_BLB N_WL N_QB UN8 NFET

******************************************
* MODELS USED IN CIRCUIT
******************************************

.MODEL NFET NMOS (LEVEL=3)

.MODEL PFET PMOS (LEVEL=3)

******************************************
* Simulations
******************************************

.print DC V(N_WL) V(N_BLB) V(N_BL) V(N_Q) V(N_QB)
.print AC V(N_WL) V(N_BLB) V(N_BL) V(N_Q) V(N_QB)
.print TRAN V(N_WL) V(N_BLB) V(N_BL) V(N_Q) V(N_QB)
.END
[/CODE]

To setup your type of analysis click Simulate and choose between: DC, AC or Transient analysis

The waveform viewer is colorful and easy to use:

I’ve used schematic capture and SPICE tools since 1978 and really wanted to like this iPad-based product, but I can say that the old way of using a mouse and keyboard are still quite superior to the tablet-based approach of using your fingers for schematic capture. Specifically, the way that you wire between ports was clumsy and not accurate because the finger is not really accurate to the pixel level which is required to place skinny wires between precise port locations. They do have a novel way for clicking and placing wires by dragging your fingers, it is just not accurate enough or fast enough for my taste.

Once you have something wired you cannot click on a net and redo vertices, you can only select and delete a wire. So, it’s not really ready for production work.

I took the 6 transistor memory cell, added a Voltage source, added the PWL syntax, and tried to netlist but couldn’t get it to accept my design. It may have just been a limitation of my demo version, and I did get some quick feedback after posting to the Facebook page.

For Spicy Schematic Capture to make the leap from proof of concept to production ready would require a few things:

  • EDIF input and output support (compatible with legacy schematics)
  • Wire vertice editing
  • Multi-sheet support
  • Price increase to support more development
  • HSPICE compatibility for the IC market

Summary
The target market for this iPad app is students and hobbyists that want a simple way to test out their design and simulation ideas. In general I think that most engineering-oriented IC designers would use the iPad as a terminal to connect to bigger iron when running their EDA software. There is a certain wow factor when using an iPad for schematics and SPICE simulation, so I commend the author for creating this new app and wish him success.

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