[WIP] Add RF transformer layout, Palace EM simulation, and Circulax parameter fit notebook

[delficomerso]

Overview

This PR adds a new notebook (nbs/palace_transformer.ipynb) that demonstrates an end-to-end workflow for designing, simulating, and extracting parameters for an integrated RF transformer.

Key Additions

• Layout Generation: Implements a parameterized transformer_concentric component (a coplanar 1:1 single-turn coil) using gdsfactory and the IHP PDK. Includes a helper function to add a Patterned Ground Shield (PGS).
• 3D EM Simulation: Sets up and runs a Driven electromagnetic simulation (10 GHz - 100 GHz) via the gsim.palace API to extract broadband S-parameters.
• Lumped-Element Modeling (WIP): Defines an equivalent circuit model for the transformer (primary/secondary coils, mutual inductance, and parasitic resistance/capacitance) using circulax.
• Parameter Extraction (WIP): Scaffolds a JAX/optax optimization routine designed to minimize the error between the circulax model's differential impedances and the Palace EM-simulated target impedances ($Z_{dd11}$, $Z_{dd22}$, $Z_{dd12}$).

Current Status (WIP)

The layout generation and Palace EM simulations are fully implemented and plotting correctly. The PR is currently marked as WIP while the parameter extraction and optax fitting loop are finalized to accurately recover the physical inductance, coupling, and parasitic values.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.04%. Comparing base (1cf9e69) to head (a18fad5).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

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+ Coverage   60.73%   61.04%   +0.31%     
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  Files          65       65              
  Lines        9665     9748      +83     
  Branches     1946     1961      +15     
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+ Hits         5870     5951      +81     
- Misses       3131     3132       +1     
- Partials      664      665       +1     

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