Building an optical transceiver with Atmel’s SAM D20

An optical transceiver can best be described as a device that converts high-speed data from a cable source (e.g., Gigabit Ethernet) to an optical signal for communication over optical fiber.

In the vast majority of configurations, a small microcontroller is used to control the Laser Driver Diode (LDD) and Linear Transconductance Amplifier (LTA) of the transceiver.

An optical transceiver is typically packed into a small form factor, simply because standards such as SFP and XFP require MCUs in the 3mm to 4mm square range.

Additional key design requirements include flexible serial and analog peripherals – with multiple LDD, LTA, host standards and interfaces requiring numerous digital and multi-channel analog interfaces. Perhaps most importantly, extremely low latency responses are necessary to control the LDD and LTA due to control loops required to sustain the high data throughput.

Atmel’s SAM D20 ARM Cortex-M0+ based MCU can be used in the design of a standard optical transceiver, along with other Atmel components, including the 30TS temperature sensor and AT24/AT25 Serial EEPROM.

“To satisfy the requirements of optical transceiver controllers, the SAM D20 offers very small package options (32QFN4x4 mm package, chip scale package <3×3 x 0.5mm), with flexible serial and analog peripherals, as well as fast and low-latency interfaces. In terms of flexible serial and multi-channel analog peripherals, Atmel’s SAM D20-based platform offers 6 SERCOM interfaces, each configurable as SPI, I2C, or USART,” Atmel engineering manager Bob Martin told Bits & Pieces.

“There is also 12-bit, 16-channel ADC, 10-bit DAC and 2 full-featured analog comparators to support multiple feedback capabilities and control interfaces. Meanwhile, fast and low-latency interfaces include optimized 300ksps, ADC and DAC analog peripherals, along with I2C, SPI, and USART serial communications interfaces – supporting up to 24Mbps data transfers, as well as single clock cycle IO control for minimal control loop latency.”

On the software side, Atmel provides an extensive development ecosystem, including debuggers development kits such as Atmel’s IDE (Studio 6), along with ready-to-run peripheral drivers and communication stacks (ASF). There is also Atmel’s Gallery and SAM D20 Xplained Pro Kit which packs an integrated programmer and debugger with connectors for expansion wings.

Additional information about Atmel’s SAM D20 MCU can be found here.