ProMOST is a single-transistor dimensioning tool for analog and RF CMOS. Size and bias
every device against your PDK's own compact model, in real time, one transistor at a time —
so your first full simulator run already starts near the optimum.
With the technology and the topology fixed, roughly three degrees
of freedom remain per transistor — three quantities picked from
{W, L, VGS, VGT, gm/ID, ID, gm},
with everything else following. A circuit with N transistors is therefore a
3N-dimensional optimization problem — and, because transistors are non-linear, a
non-linear one.
3 · 1021
combinations to examine for a 15-transistor amplifier — a 45-dimensional problem,
discretised very coarsely at just three candidate settings per dimension.
At ten settings per dimension it is 1045. It is this
growth of the search space, not the dimension count itself, that governs the work.
Coupled
Three degrees of freedom, per device
Set {W, L, VGS} and ID and gm follow; set
{L, VGT, gm} and W follows. VDS is usually not a degree of
freedom at all — only a headroom minimum to satisfy.
Non-linear
No closed-form inverse
Modern compact models — BSIM, PSP — are thousands of lines of code. You cannot invert them
to get the W that meets your spec.
The classic loop
Tweak & simulate
Grab some initial sizes, fire up the simulator, examine the collective behaviour, tweak,
re-run, tweak, re-run. Whether it converges depends entirely on the starting point.
The usual workarounds
Hand calculation, or brute-force simulation
Designers today fall back on one of two extremes. Each gives up exactly what the other has.
Back-of-the-envelope
Fast, and full of insight
Square-law models are inaccurate in modern CMOS
Oversimplification quietly hides real artifacts
Brute-force optimizer / simulator
Accurate — the full compact models
Slow: huge search space, heavy CPU load, local minima
No insight — you get numbers, not understanding
What you actually want is the accuracy of the simulator with the
speed and insight of hand analysis. That is the gap ProMOST was built to close.
The ProMOST approach
Divide & conquer: dimension per transistor
Instead of solving one enormous coupled problem, solve many small ones — each with the full,
accurate model behind it.
Mirrors, cascodes and the differential pair collapse 15 transistors into 6 unique ones.
The search space drops to 318 ≈ 4·108 — a huge gain, and still far too hard.
Optimize per transistor6 × 3 dimensions
One hard 18-dimensional search becomes six easy 3-dimensional ones, solved consecutively.
Low dimensionality means far less dependence on the initial guess. This is where ProMOST
comes in — accurately, and in real time.
Then the simulatorNear the optimum
Per-transistor optimization ignores interaction between devices, so the circuit is decently —
not fully — optimized. But the starting point is as good as it can be, which is exactly what
makes the circuit-level optimization fast.
It also tells you when the answer is "no". If the per-transistor step cannot
dimension one or more devices for their targets, that is a conflict between requirements and
design space — and it localizes the roadblock in the combination of {target specs, topology,
technology}. Either the circuit relies on an interaction that was not captured per transistor,
such as noise or distortion cancellation, or that topology in that technology simply cannot get
there.
Be in charge. Enforce what each transistor must do, individually and
collectively — instead of grabbing initial dimensions, running the simulator and reverse-engineering
the result. Design your circuit; don't reverse-engineer your simulator.
Read the full argument →
What is ProMOST
A real-time desktop calculator for transistors
ProMOST is ChipDesignWorks' transistor sizing tool for CMOS technologies: a fast desktop
calculator that lets designers determine optimum bias settings and device sizes per device —
giving very fast circuit dimensioning, straightforward porting, and clear bottleneck analysis.
Calculate operating point information for specific bias settings, device sizes and temperature
Calculate dimensions or bias conditions from a set of target performance metrics
Perform constrained or unconstrained sweeps to find the optimum
Calculate AC/RF properties: OIP, IIP, harmonic content, s-parameters and more
Work directly in VGT, gm/ID or inversion level — the vocabulary of modern design methodologies
No "Run" button. Every change to a bias setting, device size or operating
condition recalculates instantly — typical response times well below one second, even for
compound models.
The ProMOST main GUI — sweeps, operating-point data and plots update as you type.
Design speed improvement
Fourfold speed advantage
ProMOST accelerates the design process at every stage. Here is how:
01
Divide & conquer
Optimizing N transistors one by one is fundamentally faster than solving an
MN-dimensional coupled non-linear problem all at once.
02
Near-optimum starting point
Using ProMOST for initial dimensioning means your first circuit-simulator run already starts
close to the optimum — fewer, shorter iterations.
03
Simulator-accurate results
ProMOST runs the actual model in its own background solvers (op, dc, ac, noise) — results
match your circuit simulator, with sub-second response.
04
Bottleneck identification
If a transistor cannot meet its budget, you know exactly where — and why — your design is
limited.
Who it's for
Industrial designers and research groups
Industrial IC designers
Shorter design cycles — near-optimum first netlists, fewer simulator iterations.
Systematic porting — re-solve every transistor's budgets in the new PDK. Same demands, new W, L and bias. Porting becomes systematic rather than archaeological.
Bottleneck analysis for design reviews — defend every W and L with data.
Fits your flow — stand-alone, inside your design suite, or scripted from Python and MATLAB.
PhD students & university groups
Build real device intuition — explore any model parameter live, in the technology you actually tape out in.
gm/ID and VGT methodologies map one-to-one onto the tool, including the inversion coefficient.
Reproducible research — script every figure through TheRemote; export to XLS, CSV or TikZ.
Teaching — the SquareLaw and simplified-EKV add-ins put the textbook model next to a real short-channel device.
In practice
New designs, and the ones you already have
Starting from specs
Derive per-transistor budgets, dimension each device in seconds against the real model, then
enter the simulator with a near-optimum design. What follows is a short, convergent loop
rather than open-ended trial-and-error.
Hours of structured dimensioning replace days of tweak-and-simulate — and you understand
every choice you made.
Working on an existing circuit
Load a device's operating point and see immediately how far it sits from its optimum, and
which spec it limits. Re-dimension only the critical devices at constant ID or
gm — improving noise, linearity or speed without redesigning the circuit.
The same method ports a proven design to a new technology, device by device.
Accuracy & deployment
Your PDK's models, on your platform
ProMOST supports many transistor models, including
MOS11, PSP and the BSIM families, plus compound models — transistors extended with diodes,
passives and juncaps, solved as one device with both per-component and equivalent operating-point
data. It is used within major electronics companies, design houses and universities worldwide.
ProMOST runs on Linux and macOS, stand-alone or integrated in select
IC design suites. It ships with add-ins for distortion, RF small-signal, switched configurations,
W–L brute-force sweeps, bipolar devices and remote scripting.
ProMOST is updated on average once a year with bug fixes, new features, added transistor models,
and performance enhancements. A full update log is included with every software distribution
package.
