micheleandCursor
6fc2ac583d
Use the vendored Hammerstad-Jensen/Cohn engine for microstrip, stripline, and coupled-diff advice. Skip OpenEMS/pcbnew and refuse CPWG rather than inventing a number. Co-authored-by: Cursor <cursoragent@cursor.com>
81 lines
2.8 KiB
Python
81 lines
2.8 KiB
Python
"""zsolver validation: a published reference point plus monotonicity checks
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against the underlying physics, so the tests don't just re-derive whatever
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the implementation happens to compute.
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"""
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from __future__ import annotations
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import pytest
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from impedancefinder import zsolver
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def test_microstrip_matches_classic_50ohm_fr4_rule_of_thumb():
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# ~3mm trace on 1.6mm FR4 (er~4.5) is the textbook "50 ohm microstrip"
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# widely quoted in PCB fab application notes.
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z0 = zsolver.microstrip_z0(width_mm=3.0, height_mm=1.6, er=4.5, t_mm=0.035)
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assert z0 == pytest.approx(50.0, rel=0.05)
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def test_microstrip_z0_decreases_with_width():
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narrow = zsolver.microstrip_z0(0.2, 0.15, 4.3, 0.035)
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wide = zsolver.microstrip_z0(0.6, 0.15, 4.3, 0.035)
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assert wide < narrow
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def test_microstrip_z0_increases_with_dielectric_height():
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thin = zsolver.microstrip_z0(0.3, 0.1, 4.3, 0.035)
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thick = zsolver.microstrip_z0(0.3, 0.3, 4.3, 0.035)
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assert thick > thin
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def test_microstrip_z0_decreases_with_er():
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low_er = zsolver.microstrip_z0(0.3, 0.15, 3.0, 0.035)
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high_er = zsolver.microstrip_z0(0.3, 0.15, 5.0, 0.035)
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assert high_er < low_er
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def test_microstrip_z0_finite_thickness_correction_is_a_small_effect():
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with_thickness = zsolver.microstrip_z0(0.3, 0.15, 4.3, 0.035)
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without_thickness = zsolver.microstrip_z0(0.3, 0.15, 4.3, 0.0)
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assert without_thickness == pytest.approx(with_thickness, rel=0.15)
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def test_stripline_requires_positive_copper_thickness():
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with pytest.raises(ValueError):
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zsolver.stripline_z0(0.15, 0.3, 4.4, 0.0)
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def test_stripline_z0_decreases_with_width():
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narrow = zsolver.stripline_z0(0.1, 0.5, 4.4, 0.035)
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wide = zsolver.stripline_z0(0.3, 0.5, 4.4, 0.035)
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assert wide < narrow
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def test_stripline_z0_increases_with_plane_spacing():
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tight = zsolver.stripline_z0(0.15, 0.3, 4.4, 0.035)
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loose = zsolver.stripline_z0(0.15, 0.6, 4.4, 0.035)
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assert loose > tight
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def test_diff_microstrip_is_between_single_ended_and_twice_single_ended():
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single = zsolver.microstrip_z0(0.2, 0.15, 4.3, 0.035)
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diff = zsolver.diff_microstrip_z0(0.2, 0.15, 0.2, 4.3, 0.035)
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assert single < diff < 2 * single
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def test_diff_microstrip_approaches_twice_single_ended_as_spacing_grows():
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single = zsolver.microstrip_z0(0.2, 0.15, 4.3, 0.035)
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wide_gap = zsolver.diff_microstrip_z0(0.2, 0.15, 5.0, 4.3, 0.035)
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assert wide_gap == pytest.approx(2 * single, rel=0.02)
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def test_diff_stripline_approaches_twice_single_ended_as_spacing_grows():
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single = zsolver.stripline_z0(0.15, 0.3, 4.4, 0.035)
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wide_gap = zsolver.diff_stripline_z0(0.15, 0.3, 5.0, 4.4, 0.035)
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assert wide_gap == pytest.approx(2 * single, rel=0.02)
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def test_cpwg_is_not_implemented():
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with pytest.raises(NotImplementedError):
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zsolver.cpwg_z0()
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