A 10-Gb/s Wireline Receiver Using Linear Baud-Rate CDR and Analog Equalizer for Free Space Optical Communication Over 10- and 100-m Distances

Free-space wireless optical communication (FSO), which adopts the wavelength division multiplexing (WDM) technology, transmits and receives various data and wavelength combinations on a single channel. The mixed data and wavelengths are separated by WDM demodulation using the different refraction of light. Due to chromatic dispersion, the phase of the arriving optical signal would depend on the wavelength. Therefore, clock and data recovery (CDR) is required to determine the optimum sampling point in FSO-WDM systems. The proposed baud-rate CDR uses an integrator to generate a clock phase at the data center. Because the integrator output determines early or late signals, the proposed CDR does not require any reference voltage or additional clock phase. The proposed analog equalizer (AEQ) of the receiver in the front end compensates for the inter-symbol interference (ISI) caused by the electrical-to-optical converter, atmospheric channel, and optical-to-electrical converter. The AEQ reduces the ISI by using a feedback loop. The prototype receiver achieved a bit error rate (BER) of 10−11 regardless of the wavelength thanks to the proposed AEQ and baud rate CDR in FSO-WDM system over 10- and 100-m distances. The power efficiency and area of the proposed receiver were 3.8 pJ/bit and 0.147 mm2, respectively.