Crystal Oscillator Load Capacitance Calculator

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Electrical & Electronics Engineering — Circuits, Power Systems, Electronics Lab

Tranche

tranche-5

Evidence ID

t5-183

Ledger rows

1

No ledger note is attached.

Review findings

The core formulas are standard under the stated lumped-parasitic and symmetric-capacitor assumptions. Verdict is NEEDS_REVIEW because the specification leaves units, the exact meaning of Cstray, validity constraints, topology assumptions, and honest limitations unspecified. The honest label should state that results are nominal estimates for a symmetric Pierce-style load network and do not guarantee the crystal's operating frequency.

Formula and scope findings

• CL=(C1C2)/(C1+C2)+Cstray is the standard nominal load-capacitance formula when Cstray is the total effective parasitic capacitance and all capacitances use the same units.
• For the symmetric case C1=C2=C, the result C=2(CL−Cstray) is algebraically exact, not merely approximate; approximation only enters when selecting real standard capacitor values and accounting for tolerances and parasitics.
• The specification does not define whether Cstray includes the oscillator IC pin capacitances, PCB/layout capacitance, probe capacitance, or other parasitics.
• The specification does not state the required validity constraint CL>Cstray for positive external capacitors, nor does it explain how to handle CL≤Cstray.
• The two-input specification only supports the symmetric C1=C2 solution; unequal C1 and C2 values cannot be uniquely determined from CL and Cstray alone.

Unit assumptions

• CL, Cstray, C1, and C2 must be expressed in identical capacitance units; the examples use pF unless explicitly marked otherwise.
• Cstray is treated as one lumped capacitance in parallel with the crystal's effective load network.
• The crystal's rated CL is assumed to use the same load-capacitance convention as the formula.
• The reported values are nominal capacitor values before capacitor tolerance, voltage coefficient, PCB parasitics, and oscillator input-pin capacitance are included.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

The symmetric formula returns a zero-valued capacitor at the exact CL=Cstray boundary, which should be rejected for practical component selection, and very large valid-looking numeric input overflows JavaScript arithmetic to Infinity instead of producing a finite result or a clear validation error.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "crystal_rated_CL": "18 pF",
    "estimated_stray_capacitance": "3 pF",
    "assumption": "C1=C2"
  },
  "expected_outputs": {
    "C1": "30 pF",
    "C2": "30 pF"
  },
  "working": "C1=C2=2(CL−Cstray)=2(18 pF−3 pF)=2(15 pF)=30 pF. Verification: CL=(30×30)/(30+30)+3=(900/60)+3=15+3=18 pF."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche5/tranche5-results.json
• BOUNDARY_HAZARD_CATALOG.json