Optical Transceivers convert electrical data signals into blinking laser light which is then transmitted over an optical fibre. Optical transceivers have detachable optical connector to disconnect the fibre from the transceiver. Active Optical Cables (AOC) bond the fibre connection inside the transceiver end, creating a complete cable assembly.
Optical transceivers and AOC are commonly used for high-speed data communications and they normally conform to industry-standard form factors. Two popular AOC configurations are discussed in more detail below.
These industry-standard form factors dictate that designers often need to incorporate multiple power supply rails into a small physical space. As a result, power efficiency and heat dissipation become very important topics. Furthermore the latest optical transceiver chipsets also demand supplies with low output noise performance and excellent transient response.
QSFP stands for four-lane Quad Small Form factor Pluggable system. The QSFP28 variant allows speeds up to 100 Gbit/s and the closely related QSFP56 doubles the top speed to 200 Gbit/s.
Simpler QSFP28 designs often use non-return-to-zero modulation (NRZ) and normally an additional DSP and extra negative voltage rail is not required. However, QSFP56 designs typically use 4-level Pulse Amplitude Modulation (PAM4) and NRZ so an additional negative voltage rail is often required for the EML (electro-absorption modulated laser).
A typical QSFP-100G block diagram is illustrated below:
Fig.1: Typical Optical Transceiver circuit configuration (QSFP-100G).
QSFP-DD is a module and cage/connector system like the QSFP above, but it includes an additional row of contacts providing for an eight-lane electrical interface. It provides solutions up to 200 Gbps or 400 Gbps aggregate and typically uses PAM4 as well as NRZ modulation.
Typically, QSFP-DD designs include an additional Digital Signal Processor (DSP) for PAM4 and an additional negative voltage rail for the EML is normally required.
A typical QSFP-DD block diagram is illustrated below:
Fig.2: Typical Optical Transceiver circuit configuration (QSFP-DD).
TOSA (Transmitter Optical Sub Assembly)
TX CDR (Transmitter Clock Data Recovery)
EML Driver (Electro-absorption Modulator Laser Driver)
EML (Electro-absorption Modulator Laser)
XCL303 - Negative Output Voltage Micro DC/DC with Integrated Coil
TEC (Thermo Electric Cooler)
ROSA (Receiver Optical Sub Assembly)
XCL102 - Step-Up Micro DC/DC with Integrated Coil
For when > 3.3 V is required to suppress laser temperature drift
DSP (Digital Signal Processor)
PAM4 (Pulse Amplitude Modulation)
PHY (PHYsical layer)
XCL213 - 1.5 A Hi-SAT COT Step-Down Micro DC/DC with Integrated Coil
For DSP and microprocessor core Voltage
XC9266 - 6.0 A Hi-SAT COT Step-Down DC/DC
For DSP core, low voltage
Power on Reset to monitor 3.3 V rail
XC6127 - Voltage detector with Delay
Samples of all the Torex IC mentioned above are readily available, so please ask your local Torex representative for details or contact us directly.