Optical Transceiver

Optical transceivers are commonly used for high speed data communications and they normally conform to industry standard form factors. This results in designers often needing to incorporate multiple power supply rails into a small predetermined physical space.

Efficiency and power dissipation become very important and the latest optical transceiver chipsets demand supplies with low output noise performance and excellent transient response.

Circuit configuration of Optical Transceiver (QSFP-DD)
Circuit configuration of Optical Transceiver (QSFP-100G)

Optical Transceiver (QSFP-DD)

QSFP-DD is a module and cage/connector system similar to current QSFP, but with an additional row of contacts providing for an eight lane electrical interface. It provides solutions up to 200 Gbps or 400 Gbps aggregate and uses PAM4 (4-level Pulse Amplitude Modulation) as well as NRZ modulation.

Typically QSFP-DD designs include an additional Digital Signal Processor (DSP) for PAM4 and they also require a negative voltage rail for the PAM4 EML (a laser source plus electro-absorptive modulator)

Block diagram	Requirements	Recommended ICs	Features
Line Switch For 3.3V input	Specifications I_OUT: 6A Other points Adjustable Slew Rate	-	-
Power on Reset To monitor 3.3V rail	Specifications Detect voltage: 2.7V Other points Small High accurate	XC6127	High accurate voltage detector Small High accurate V_IN: 0.7V ~ 6.0V Detect voltage: 1.5V ~ 5.5V
TOSA (Transmitter Optical SubAssembly) TX CDR (Transmitter Clock Data Recovery) EML Driver (Electro-absorption Modulator Laser Driver) EML (Electro-absorption Modulator Laser)	Specifications V_OUT: -1.2V ~ -3.3V I_OUT: 50mA ~ 300mA Other points Small Low noise High efficiency	XCL303	Inductor built-in Negative Output Voltage DC/DC Suitable negative voltage supply for Laser Driver and EA Low ripple, good for Laser stability Small, Low noise V_IN: 2.7V ~ 5.5V V_OUT: -1.2V ~ -6.0V I_OUT max: 300mA @ V_OUT=-3.3V, V_IN=3.3V
	Specifications V_OUT: 0.9V ~ 2.5V I_OUT: 100mA ~ 300mA Other points Small Low noise High efficiency	XCL223 / XCL219	Inductor built-in HiSAT-COT step-down DC/DC Small and low height package (XCL223, h=0.75mm max.) High speed transient response, Low noise V_IN: 2.5V ~ 5.5V V_OUT: 0.8V ~ 3.6V I_OUT max: 700mA (XCL223) / 1A (XCL219)
TEC (Thermo Electric Cooler)	Specifications V_OUT: 3.3V ~ 5.0V I_OUT: 100mA ~ 300mA Other points Small High efficiency	XCL102	Inductor built-in step-up DC/DC When> 3.3V is required to suppress laser temperature drift Small, Low ripple V_IN: 0.6V ~ 5.5V V_OUT: 1.6V ~ 3.6V I_OUT max: 500mA @ V_OUT=5.0V, V_IN=3.3V
DSP(Digital Signal Processor) PAM4(Pulse Amplitude Modulation) PHY(PHYsical layer)	Specifications V_OUT: 0.6V ~ 1.2V I_OUT: 3A ~ 6A Other points High accurate High speed transient response	XC9266	6A high speed transient response HiSAT-COT step-down DC/DC For DSP core, low voltage High speed transient response HiSAT-COT control For low height of module (h=1.0mm) V_IN: 2.5V ~ 5.5V V_OUT: 0.6V ~ 3.6V I_OUT max: 6A
ROSA(Receiver Optical Sub Assembly)	Specifications V_OUT: 3.3V ~ 5.0V I_OUT: 100mA ~ 300mA Other points Small Low noise High efficiency	XCL102	Inductor built-in step-up DC/DC Small, low ripple V_IN: 0.6V ~ 5.5V V_OUT: 1.6V ~ 3.6V I_OUT max: 500mA @ V_OUT=5.0V, V_IN=3.3V

Optical Transceiver (QSFP-100G)

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 use non-return-to-zero (NRZ) modulation and normally an additional DSP and extra negative voltage rail is not required . QSFP56 uses PAM4 so an additional negative voltage rail for the PAM4 EML is often required.

Block diagram	Requirements	Recommended ICs	Features
Line Switch For 3.3V input	Specifications I_OUT: 3A Other points Adjustable Slew Rate	-	-
Power on Reset To monitor 3.3V rail	Specifications Detect voltage: 2.7V Other points Small High accurate	XC6127	High accurate voltage detector Small High accurate V_IN: 0.7V ~ 6.0V Detect voltage: 1.5V ~ 5.5V
TOSA (Transmitter Optical SubAssembly) TX CDR (Transmitter Clock Data Recovery) EML Driver (Electro-absorption Modulator Laser Driver) EML (Electro-absorption Modulator Laser)	Specifications V_OUT: -1.2V ~ -3.3V I_OUT: 50mA ~ 300mA Other points Small Low noise High efficiency	XCL303	Inductor built-in Negative Output Voltage DC/DC Suitable negative voltage supply for Laser Driver and EA Low ripple, good for Laser stability Small, Low noise V_IN: 2.7V ~ 5.5V V_OUT: -1.2V ~ -6.0V I_OUT max: 300mA @ V_OUT=-3.3V, V_IN=3.3V
	Specifications V_OUT: 0.9V ~ 2.5V I_OUT: 100mA ~ 300mA Other points Small Low noise High efficiency	XCL223 / XCL219	Inductor built-in HiSAT-COT step-down DC/DC Small and low height package (XCL223, h=0.75mm max.) High speed transient response, Low noise V_IN: 2.5V ~ 5.5V V_OUT: 0.8V ~ 3.6V I_OUT max: 700mA (XCL223) / 1A (XCL219)
TEC (Thermo Electric Cooler)	Specifications V_OUT: 3.3V ~ 5.0V I_OUT: 100mA ~ 300mA Other points Small High efficiency	XCL102	Inductor built-in step-up DC/DC Small, Low ripple V_IN: 0.6V ~ 5.5V V_OUT: 1.6V ~ 3.6V I_OUT max: 500mA @ V_OUT=5.0V, V_IN=3.3V
uPC(microcontroller)	Specifications V_OUT: 1.8V ~ 3.3V I_OUT: 100mA ~ 300mA Other points Small High efficiency	XCL223	Inductor built-in HiSAT-COT step-down DC/DC Small / Low height package (h=0.75mm max.) High speed transient response, Low noise V_IN: 2.5V ~ 5.5V V_OUT: 0.8V ~ 3.6V I_OUT max: 700mA
RX CDR (Receiver Clock Data Recovery)	Specifications V_OUT: 1.8V ~ 3.3V I_OUT: 100mA ~ 300mA Other points High accurate Low noise	XCL223 / XCL219	Inductor built-in HiSAT-COT step-down DC/DC Ideal for preventing data errors with low ripple Small / Low height package (XCL223, h=0.75mm max.) High speed transient response, Low noise V_IN: 2.5V ~ 5.5V V_OUT: 0.8V ~ 3.6V I_OUT max: 700mA (XCL223) / 1A (XCL219)
ROSA (Receiver Optical Subassembly)	Specifications V_OUT: 3.3V ~ 5.0V I_OUT: 100mA ~ 300mA Other points High accurate Low noise	XCL102	Inductor built-in step-up DC/DC Small, Low ripple V_IN: 0.6V ~ 5.5V V_OUT: 1.6V ~ 3.6V I_OUT max: 500mA @ V_OUT=5.0V, V_IN=3.3V

Optical Transceiver AOC（Active Optical Cable）
IoT Devices (Battery operation, Low power consumption )
Industrial Sensors (12V / 24V power supply)
Small Li batteries rechargeable by LDO (nominal 2V to 3V)