AN OPTOELECTRONIC THYRISTOR BASED ANALOG TO DIGITAL CONVERTER

A unique thyristor laser implements a high performance Analog to Digital Converter (ADC) in a monolithic FET GaAs integrated circuit. In the curent high speed FLASH ADC, the comparator circuit performs in the sampling on the input analog signal by comparing it to a voltage reference tree and the outputs are converted to binary form via a decimal to binary (DTB) algorithm stored in a ROM. To achieve substantial increases in ADC accuracy, speed and circuit density, we propose a comparator based on an optoelectronic thyristor which is electrically switched and provides laser ouput as a VCSEL in the on state. We introduce an elegant new architecture to implement the ADC function which merges the roles of the quantization, the DTB conversion and the O/E conversion within a simple integrated circuit. One thyristor and one Differential amplifier are required per binary digit. This new approach reduces the number of devices required for a 12 bit ADC from 100,000 to 70 and reduces the ADC delay from 50ns to 0.5ns. The power is correspondingly reduced and the output is a digital optical signal in serial or parallel format. The voltage resolution is in the 5mV range limited only by the dark current noise in the switch. This approach provides a quantum leap in an N bit ADC speed because the output is obtained optically in the time that it takes the analog signal to ripple through N stages at 40ps/stage. This technique promises to revolutionize the art of ADC and to provide the basis for very high speed image transfer for the future all digital network. In addition to this novel conversion we also provide the integrated technology to realize the VCSEL thyristor, the FET amplifier and CCD sensor simultaneously.