Source: https://guthlabs.ai/docs/instruments/bjt-amplifier-gain-estimator-common-emitter/
instrument / verified-with-binding-errata
# BJT Amplifier Gain Estimator (Common-Emitter)
The current ledger marks this instrument verified with errata that must be applied at binding time.
Status: **VERIFIED_WITH_ERRATA**Lifecycle: **verified-with-binding-errata**
## Inspectable records
[01**Overview**Purpose and lifecycle]()[02**Mechanism**Method and assumptions]()[03**Implementation**Binding and validation]()[04**Qualification**Evidence and errata]()
## Ledger state
The current ledger marks this instrument verified with errata that must be applied at binding time.
**Area**: Electrical & Electronics Engineering — Circuits, Power Systems, Electronics Lab
**Tranche**: tranche-5
**Evidence ID**: t5-171
**Ledger rows**: 1
No ledger note is attached.
## Review findings
The honest label 'simplified hybrid-π small-signal model' is directionally accurate but incomplete. The UI should explicitly label the results as unloaded, emitter-AC-grounded estimates and state the IE derivation, thermal-voltage assumption, and omitted ro/RL/emitter-degeneration effects.
### Formula and scope findings
- re=26 mV/IE is standard only at approximately room temperature; the 26 mV thermal-voltage assumption should be stated explicitly.
- IE is not provided as an input. The specification provides IC and β, but does not state whether to approximate IE≈IC or derive IE=IC(1+1/β). The test vectors use the latter relationship.
- Av≈−RC/re is valid for an unloaded common-emitter stage with the emitter AC-grounded; it omits emitter degeneration, collector load RL, and transistor output resistance ro.
- Zout≈RC assumes ro is much larger than RC and omits any external load. A more complete approximation is RC||ro, with the load included when relevant.
- Zin≈R1||R2||βre assumes R1 and R2 are AC-grounded bias resistors and uses the simplified base-input resistance βre; it omits transistor bias-dependent parameter variation and other input loading.
### Unit assumptions
- IC and IE are currents in amperes when used with 0.026 V; resistor values are in ohms; β is dimensionless.
- 26 mV is treated as the room-temperature thermal voltage VT.
- For the test vectors, IE is derived as IE=IC(1+1/β), rather than approximated as IC.
- Av is dimensionless; Zin and Zout are in ohms; the minus sign denotes common-emitter phase inversion.
## Boundary hardening
**BREAK_CLAIMED** · SELF_FLAGGED
The valid-looking boundary input IC=0 makes re=26 mV/IE divide by zero, causing Av and Zin to be undefined. The estimator must reject zero collector/emitter current instead of forcing numeric results.
## Errata and corrections
### Tranche errata
**Zin** · vector 3
33015.873
32974.001
final reciprocal of her own correct conductance sum divided slightly wrong
## Inspectable example
4 review vectors are recorded. One source-bound sample is shown below.
````
{
"inputs": {
"IC": "1.000 mA",
"RC": "4700 Ω",
"R1": "100000 Ω",
"R2": "20000 Ω",
"β": 100
},
"expected_outputs": {
"Av": -182.576923,
"Zin": "2229.846 Ω",
"Zout": "4700 Ω"
},
"working": "IE=IC(1+1/β)=0.001(1+1/100)=0.00101 A. re=0.026/0.00101=25.742574 Ω. Av=−4700/25.742574=−182.576923. βre=100×25.742574=2574.2574 Ω. Zin=1/(1/100000+1/20000+1/2574.2574)=1/(0.00001+0.00005+0.000388461538)=1/0.000448461538=2229.846 Ω. Zout=RC=4700 Ω."
}
````
## 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_WITH_ERRATA`
- `evidence-tranche5/tranche5-results.json`
- `BOUNDARY_HAZARD_CATALOG.json`