Sub-THz sampling AD converters using resonant tunneling diodes

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The purpose of this project is to establish high performance Analog to Digital Conversion (ADC) technology using resonant tunneling logic gate MOBILES (Monostable Bistable Transition Logic Elements). We investigated a novel type of Delta Sigma ADC, which uses frequency modulated intermediate signals (FM Delta Sigma ADC). The details of the studies are shown below.1. First, we proposed a novel resonant tunneling logic gate, SMOBILE (Symmetric MOBILE). The SMOBILE can operate at double-clock rate. Furthermore, its operation is scarcely affected by the output current. These features make the SMOBILE promising for ultrahigh speed operations. 100 Gb/s operation is demonstrated with complementary 50 GHz clocks for circuits fabricated on InP substrates. The SMOBILE is promising for quantizers for high-performance analog-digital converters.2. The output signal of the MOBILE is in a RZ-mode (Return to Zero). This obstructs integration of the MOBILE circuits into conventional circuits. Here we proposed NRZ-MOBILE (Non Return to Zero MOBILE), the output of which is compatible to the conventional circuits. After confirming the basic operation of the NRZ-MOBILE, we investigated its application to the FMDSM (FM Delta Sigma Modulator), which is a key component of the FM Delta Sigma ADCs. Even if we take the threshold voltage fluctuation of the HEMTs into account, good SNDR (Signal to Noise and Distortion ratio) was demonstrated for FMDSM using the NRZ-MOBILE. Moreover, we confirmed SNDR improvement for parallel FMDSM using NRZ-MOBILEs.3. One of the most difficult problems of the FMDSM is to improve linearity of the voltage controlled oscillator (VCO). We proposed complementary VCO approach to solve this problem, where two VCOs are driven by the complementary input signals. It is demonstrated the 2nd harmonic peak can be decreased and the good SFDR can be obtained by this scheme.