Reading a transceiver datasheet

A transceiver datasheet is twenty pages of tables, and the three numbers that decide whether a link works are scattered across them under different names and test conditions. This page walks through the standard structure of a datasheet, explains the transmitter, receiver, electrical, environmental and management parameters that matter, shows how to normalise "min/typ/max" claims between vendors, and ends with a unified specification card — the fields to record for every module you qualify.

Structure of a datasheet

Section	What it contains	What to check
Features / applications	marketing bullets: PMD, reach, DDM, RoHS, MSA compliance	PMD names and standards referenced (Standards map)
Ordering information	PN table: grades, connector, DDM options	grade suffixes (Temperature grades, Part numbering)
Absolute maximum ratings	supply, storage temperature, input power that damages	receiver damage threshold
Recommended operating conditions	Vcc, case temperature, data rate, supply current / power	class and grade (Power & consumption)
Optical characteristics — transmitter	wavelength, power, OMA, ER, spectral width, eye, TDECQ	the min values
Optical characteristics — receiver	sensitivity, overload, LOS thresholds, return loss	at which BER and conditions
Electrical characteristics	input/output swing, impedance, CDR, jitter, control pins	host compatibility
Timing	t_init, t_off, t_on, LOS assert/deassert, DDM update	bring-up behaviour
Digital diagnostics	SFF-8472/8636/CMIS compliance, calibration type, accuracy, alarm defaults	calibration and accuracy (Accuracy)
Pin assignment / mechanical drawing	MSA pinout, dimensions, latch, heat-sink notes	cage fit
EEPROM content	default identity bytes, sometimes a full A0h dump	vendor fields, compliance codes (Memory map)
Regulatory / reliability	laser class, CE/FCC/RoHS, MTBF, ESD ratings	—
Revision history	what changed between datasheet versions	firmware or spec changes

Transmitter parameters

Parameter	Typical spec (10GBASE-LR example)	Meaning	Pitfall
Centre wavelength	1260–1355 nm (1310 nominal)	laser λ window over temperature and life	CWDM/DWDM windows are tighter; check at the grade's extremes
Spectral width	−20 dB width ≤ 1 nm (DFB); RMS ≤ 0.85 nm (VCSEL 850)	linewidth → dispersion penalty	wide width limits reach on SMF
SMSR	≥ 30 dB	single-mode purity	—
Average launch power	−8.2 … +0.5 dBm	Pavg into the fibre	min defines budget; "typ −3 dBm" is marketing
OMA	≥ −5.2 dBm	modulated amplitude P1 − P0	Ethernet specs use OMA; DDM reports average
Extinction ratio	≥ 3.5 dB	P1/P0	low ER raises average-power needs; conversion below
Eye mask margin / TDP	mask per IEEE; TDP ≤ 3.2 dB	waveform quality / dispersion penalty	TDECQ ≤ 3.4 dB for PAM4
RIN	≤ −128 dB/Hz (RIN12OMA)	laser noise	matters for high-ER links
Tx off power	≤ −30 dBm	TX_DISABLE effectiveness	—

Conversion: Pavg = OMA × (ER + 1) / (2 × (ER − 1)) in linear units; for ER = 3.5 dB (2.24×), Pavg ≈ 1.3 × OMA/… — in dB: Pavg ≈ OMA + 1.2 dB. Details in Units & conversions.

Receiver parameters

Parameter	Typical spec	Meaning	Pitfall
Sensitivity (average)	≤ −14.4 dBm at BER 1e-12 (10G LR); ≤ −10.6 dBm OMA (stressed)	weakest signal decoded at the stated BER	the BER matters: 25G+ specs quote pre-FEC BER 2.4e-4 or 1e-5 — not comparable with 1e-12 figures
Stressed receiver sensitivity	worse than nominal by the stress penalty	with a distorted test signal — the realistic figure	some datasheets omit it
Receiver overload / saturation	≥ +0.5 dBm	strongest signal still decoded	a 40 km module on 2 km needs an attenuator (Rx power & budget)
Damage threshold	+3 … +5 dBm (absolute max)	destroys the photodiode	high-power ER/ZR ends, amplified systems
LOS assert / deassert	assert ≤ −30 dBm, deassert ≥ −20 dBm, hysteresis ≥ 0.5 dB	when the LOS pin toggles	LOS deasserting far above sensitivity hides marginal links
Return loss	≥ 12 dB (MMF) / 26 dB (SMF APC systems)	reflection back into the fibre	—
Receiver wavelength range	1260–1600 nm	photodiode response	BiDi and CWDM receivers may be filtered

Link parameters

Parameter	What it says	Check
Link budget / power budget	Tx min − Rx sensitivity, e.g. 6.2 dB for 10G LR at 1e-12	subtract fibre, connectors, splices, penalties, margin (Reach tables)
Reach	standard figure at standard fibre	conditions (OM3 vs OM4; SMF at 0.4 dB/km)
Dispersion tolerance	ps/nm (e.g. 800 ps/nm for 40 km at 1550)	for long SMF links and DWDM
Penalties	TDP, stressed eye, jitter	already inside the budget in IEEE specs; vendor tables may list them separately

Electrical and timing

Parameter	Typical (SFP+/SFF-8431)	Notes
Supply	3.3 V ± 5 %; max current per class	Power & consumption
Data rate	9.95–11.3 Gb/s (10G LR) / 25.78 Gb/s / 26.5625 GBd PAM4	multi-rate windows; below-range rates may not lock (Speed & rate)
Input differential swing	180–700 mVpp (SFI)	host output must fit
Output differential swing	300–850 mVpp	—
CDR	present / bypassable / rate-selectable	CDR
t_init (power-on to ready)	≤ 300 ms (SFP+) ; CMIS modules seconds	host waits before reading
t_off (TX_DISABLE assert → light off)	≤ 10 µs	—
t_on (TX_DISABLE negate → light on)	≤ 1 ms	—
LOS assert / deassert time	≤ 100 µs	—
DDM update interval	100 ms … 1 s	slower than the host polls
Hardware pins	TX_DISABLE, TX_FAULT, RX_LOS, RS0/RS1, MOD_ABS; QSFP: ResetL, LPMode, IntL, ModSelL	SFP hardware, QSFP hardware

Environmental, reliability, regulatory

Item	Look for
Case temperature	0…70 / −5…85 / −40…85 °C (Temperature grades)
Humidity	5–85 % (or 95 %) RH non-condensing
MTBF	hours at 25 or 40 °C (Telcordia SR-332) — 1–5 million hours is typical marketing; wear-out is not MTBF (Failures)
ESD	HBM ≥ 1 kV on data pins, ≥ 2 kV on connector shell
Laser safety	Class 1 (IEC 60825-1), CDRH 21 CFR 1040.10 (Labels)
Compliance	RoHS, CE, FCC, UL

Management section

Item	Meaning
"SFF-8472 Rev 12.x compliant, DDM"	A2h diagnostics present (SFF-8472)
Internal / external calibration	how the host converts raw values (Calibration)
DDM accuracy	±3 dB power, ±3 °C, ±10 % bias typically (Accuracy)
Alarm/warning defaults	factory thresholds (Thresholds)
Write protection / password	whether user area is writable (Write protection)
CMIS version, applications, VDM support	for QSFP-DD/OSFP (CMIS)

Min, typ, max and test conditions

Budget uses min Tx and the worst (least negative) sensitivity. Typical numbers describe a sample at 25 °C, not the part you will get at +70 °C after five years.
BER basis. 1G/10G/FC quote 1e-12. 25G, 50G, 100G and PAM4 specs quote pre-FEC BER (2.4e-4 for RS-FEC; 1e-5 for some KP4 cases) — a "−10 dBm sensitivity" at 2.4e-4 is not better than "−14 dBm" at 1e-12 (FEC).
OMA vs average. Ethernet PMDs specify OMA; DDM shows average power; convert before comparing (Units).
Temperature range. Optical specs are guaranteed over the case range of the grade; a −40…85 part's numbers hold at the extremes, a 0…70 part's do not beyond them.
End of life. IEEE budgets include EOL Tx degradation; vendor "typ" does not.
Fibre assumptions. Reach on OM3 vs OM4; SMF at 0.4 vs 0.35 dB/km; connectors counted (1.5 dB for MMF, 2 × 0.5 dB for SMF typically).

Comparing two modules

Same PMD and standard clause? (LR vs "LR-compatible" vs LX.)
Same grade and case range?
Tx min and Rx sensitivity at the same BER → budget.
Power consumption max and class → cage fit.
DDM: calibration type, accuracy, thresholds.
Management compliance and revision; CMIS version for 400G+.
MSA mechanical compliance, latch type, heat-sink requirement.
EEPROM identity policy: OEM-coded, generic, or configurable (Third-party optics).

A unified specification card

Record these fields for every qualified module; they map one-to-one to what CodingBox reads and to what a switch checks.

Field	Example	Source
Vendor / PN / rev	Acme / SFP-10G-LR-A / A2	label, EEPROM
Form factor	SFP+	EEPROM byte 0
PMD / standard	10GBASE-LR, IEEE 802.3 Cl. 52	compliance codes
Data rate(s)	9.95–11.3 Gb/s	datasheet, BR nominal byte
Wavelength	1310 nm (1260–1355)	byte 60–61
Fibre / connector	SMF, LC duplex, UPC	connector byte
Reach	10 km	length bytes
Tx power min / max	−8.2 / +0.5 dBm	datasheet
Rx sensitivity / overload	−14.4 / +0.5 dBm at 1e-12	datasheet
Link budget	6.2 dB	derived
Power class / max power	Level I / 1.0 W	byte 64; datasheet
Case temperature	0…70 °C	datasheet, PN suffix
DDM	yes, internal calibration, ±3 dB	byte 92; datasheet
Management spec	SFF-8472 Rev 12.4	byte 94
Laser class	Class 1	label
Coding	generic / coded for X	EEPROM vendor fields
Firmware	1.02	vendor area
Qualification result	pass on platform Y, release Z, date	test log

In CodingBox

Half of the card comes from the EEPROM: CodingBox reads form factor, compliance codes, wavelength, lengths, power class, DDM type and calibration, management revision and vendor identity in one pass, and the code database stores them per PN together with your datasheet-derived fields (Check transceiver).