Filter Designer — Active Sallen-Key (2nd order) implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t6-013

Effect

Computation or source lookup only

Input and validation requirements

The advertised input Q is not independently realizable in the stated unity-gain equal-component approximation: that topology fixes Q at 0.5, so any requested Q other than 0.5 cannot be met without changing component ratios or adding gain. The engine also reaches an undefined division at fc=0 and can misdesign by a factor of 2π if Hz versus rad/s is not explicit.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "fc_hz": 1000,
    "Q": 0.5,
    "filter_type": "LP",
    "design_assumption": "C1=C2=10 nF; unity gain K=1; R1=R2"
  },
  "expected_outputs": {
    "R1_ohm": 15915.494309,
    "R2_ohm": 15915.494309,
    "C1_F": 1e-8,
    "C2_F": 1e-8,
    "achieved_fc_hz": 1000,
    "achieved_Q": 0.5
  },
  "working": "Set C1=C2=C=10 nF=10×10^-9 F and R1=R2=R. Then fc=1/(2πRC), so R=1/(2πfcC)=1/(2×3.141592653589793×1000×10×10^-9)=1/(0.0000628318530718)=15915.494309 Ω. For unity gain K=1, Q=1/(3-K)=1/(3-1)=0.5. Therefore R1=R2=15915.494309 Ω and C1=C2=10 nF."
}

Other records

Sources and evidence

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

• VERIFIED_LEDGER.json
• evidence-tranche6/tranche6-results.json