Ultrahigh frequency integrated circuits using resonant tunneling diodes

The purpose of this project is to establish ultrahigh speed integrated circuit technology using resonant tunneling diodes (RTDs). The project is divided into three parts ; 1) to develop high performance analog to digital converters (ADC) based on resonant tunneling logic gate, MOBILE, 2) to develop logic gates based on the MOBILE having ultra short gate delay time of around 100 fs, 3) to develop ultrahigh frequency chaos circuits and their applications. The details of the studies are shown below.1) The MOBILE is a high speed logic gate exploiting the monostable to bistable transition of a circuit consisting of two serially connected RTDs. It features edge-trigger and latching function as well as short switching time. These features make it suitable for the quantizer application in ADCs. We investigated the delta sigma ADC using the MOBILE, since the performance of which strongly depends on the operating frequency, and requires no precise analog component. We proposed a novel delta sigma modulator using a MOBILE, which is based on the FM delta sigma modulation concept. We demonstrated ultrahigh frequency operation of delta sigma modulator at 20GHz. Furthermore, we proposed novel technique to surmount difficulties of FM delta sigma modulation, which have hindered the use of FM delta sigma modulation.2) The C^2MOBILE (Capacitor-Coupled Monostable-Bistable Transition Logic Element) is an extension of the MOBILE. The C^2MOBILE uses the transient current through the coupling capacitor to transmit signals between gates, and is expected to operate with an extremely short gate delay time. Basic operations of the C^2MOBILE have been demonstrated with the circuits fabricated on InP substrates. The circuit tested are the 2- and 3-stage logic circuits and the AND/OR gate. The gate delay time was estimated to be around 1 ps for these circuits. Much shorter gate delay time close to 100 fs should be possible with the sophisticated circuit design and fabrication process.3) We proposed the RTD chaos generator and its application to a variable-ratio frequency-divider, which is based on the bifurcation phenomenon characteristic of chaos systems. 88 GHz operation of 1/2 frequency divider was demonstrated using this circuit. Furthermore, we proposed a technique to control chaos in this system. Using this technique we demonstrated direct observation of the chaotic signals in the microwave frequency range.