A fiber-optic analog isolator of up to 10 MHz bandwidth

Abstract

The electromagnetic interference (EMI) around the Experimental Advanced Superconducting Tokamak (EAST) device is very harsh during plasma discharge experiment. In order to reduce the effect of EMI and enhance signal to noise ratio (SNR), a fiber-optic high speed isolator has been designed. Each channel of the isolator has a transmitter unit connected via fiber-optic cable to the receiver unit. A transmitter unit which consists of a 6th order Bessel low-pass anti-aliasing filter, an analog-to-digital converter (ADC), a Field Programmable Gate Array (FPGA), a serializer and an optical transceiver, while a receiver unit comprises an optical transceiver, a deserializer, a FPGA, a digital–to-analog converter (DAC) and a 6th order Bessel low-pass filter. Data from the ADC is serialized by the serializer using 8b/10b encoding before transmission, and 10b/8b decoding was used by the deserializer in the receiver unit. A prototype of this isolator has been realized and tested. The test results show that the transmission bandwidth of analog signal is up to 10MHz, the transmission delay is typically 500ns, the transmission distance is up to 250m and the output noise is less than 5mV, which can meet the requirements of EAST experimental campaigns.