CT-1250NSP-SB1L-A 850 nm VCSEL 550 m 1.25 Gb/s SFP Transceiver

The CT-1250NSP-SB1L-A supports distances up to 550 m over 50/125 µm multimode fibre and 275 m over 62.5/125 µm multimode fibre. It uses an 850 nm VCSEL with an optical output range of −9.5 to −4 dBm and a receiver sensitivity of −17 dBm or better. The difference between the weakest specified transmitter output and receiver sensitivity is 7.5 dB. This figure is the unallocated optical power difference rather than a complete channel budget, so connector loss, splice loss, modal effects and ageing allowances must still be considered. The installed fibre type and channel loss should therefore be verified before the maximum distance is adopted in a design.

Yes, the module is intended for IEEE 802.3z Gigabit Ethernet at 1.25 Gb/s and ANSI Fibre Channel links operating at 1.06 Gb/s. The electrical interface uses NRZ signalling, so the host serializer and receiver circuitry must provide the correct line rate for the selected protocol. Pin 7, which is assigned as Rate Select in the SFP connector format, is not connected in this module. The transceiver should therefore be treated as a fixed-function optical device rather than a host-controlled multi-rate module. Link compatibility still depends on the host port, protocol configuration, optical budget and multimode fibre characteristics.

The module requires a nominal 3.3 V supply and is specified to operate from 3.1 to 3.5 V. Maximum transmitter and receiver supply currents are 140 mA and 100 mA respectively, giving a combined stated maximum of 240 mA. The host power rail and filtering network should be designed above this requirement with an appropriate engineering margin. The differential data input accepts a voltage swing from 400 to 1,660 mV, while the receiver differential output is specified from 0.4 to 1.3 V. The 6 V absolute maximum rating must not be interpreted as an allowable operating voltage, as normal operation is restricted to the 3.1–3.5 V range.

The receiver sensitivity is specified at −17 dBm or better, while the maximum optical input power is −3 dBm. These limits define a 14 dB span between the sensitivity threshold and overload level. The transmitter output ranges from −9.5 to −4 dBm, leaving 1 dB between the strongest specified transmitter output and the receiver overload limit before channel losses are introduced. Very short laboratory or equipment-level links should still be checked for measurement tolerance and unexpected power variation. At the weak-signal end, the −17 dBm sensitivity is associated with a 2^7−1 test pattern and a bit error rate below 10^−12, so production testing should use equivalent acceptance criteria where required.

TX_DISABLE is active high, and leaving the input open also disables the transmitter. A low level is defined between 0 and 0.8 V, while a high level extends from 2.0 V to Vcc. TX_FAULT provides a transmitter fault indication, and RX_LOS reports insufficient received optical power using TTL-compatible output levels. The specified LOS thresholds are −30 dBm for assertion and −17 dBm for deassertion, with 0.5 dB of stated hysteresis. Host firmware should also account for the timing limits, including up to 300 ms for initialisation, 10 µs for TX_DISABLE assertion and 100 µs for RX_LOS assertion or deassertion.

The specified case operating temperature is −40 to +85 °C, and the storage temperature range is also −40 to +85 °C. The operating limit applies to the module case, so enclosure ambient temperature alone is not sufficient for thermal validation. Airflow, cage temperature, neighbouring heat sources and the module’s combined current consumption must be included when assessing the thermal design. The optical transmitter is designed for Class 1 operation under EN 60825-1, while the construction is identified as RoHS compliant and lead-free. EMC behaviour is designed around FCC Class B limits, although the completed host equipment still requires system-level emissions and immunity assessment.

The module uses the SFP form factor, a 20-pin electrical connector and a duplex LC optical receptacle. Integration therefore requires a compatible SFP cage, host connector and transmit and receive fibre arrangement. The high-speed electrical paths are provided through TD+/TD− and RD+/RD− differential pairs, with separate transmitter and receiver power and ground pins. Rate Select is not connected, while MOD-DEF(0), MOD-DEF(1) and MOD-DEF(2) support module presence and serial identification functions. PCB routing should maintain the intended differential impedance, minimise discontinuities and use suitable supply filtering close to the cage connection.

Digital diagnostic monitoring is not specified for the CT-1250NSP-SB1L-A. The MOD-DEF(1) and MOD-DEF(2) pins are assigned to a two-wire serial identification interface, but that assignment alone does not confirm support for real-time temperature, voltage, bias-current or optical-power telemetry. A host design should not assume compatibility with DDM or DOM management functions. Link supervision can still use the dedicated RX_LOS and TX_FAULT outputs, together with transmitter control through TX_DISABLE. If live optical and electrical telemetry is mandatory, that capability should be confirmed before the module is approved for the application.