Resonant Tunneling Analog-To-Digital Converter

As sampling rates continue to increase, current analog-to-digital converter (ADC) device technologies will soon reach a practical resolution limit. This limit will most profoundly effect satellite and military systems used for e.g. electronic countermeasure, electronic and signal intelligence, and phased-array radar. New device and circuit concepts will be essential for continued progress. We will describe a novel, folded architecture ADC which could enable a technological discontinuity in ADC performance. The converter technology is based on the integration of multiple resonant tunneling diodes (RTD) and heterojunction transistors on an indium phosphide substrate. The RTD consists of a layered semiconductor heterostructure AIAs/InGaAs/AIAs (2/4/2 nm) clad on either side by heavily-doped InGaAs contact layers. Compact quantizers based around the RTD offer a reduction in the number of components and a reduction in the input capacitance. Because the component count and capacitance scale with the number of bits N, rather than by 2 N as in the flash ADC, speed can be significantly increased. A 4-bit, 2-GSps quantizer circuit is now under development to evaluate the performance potential. Circuit designs for ADC conversion with a resolution of 6-bits at 25 GSps may be enabled by the resonant tunneling approach.