Analog-to-digital converter using resonant tunneling diodes.

摘要

A novel A/D converter structure based on the Resonant Tunneling Diode (RTD) is presented. By using RTDs, the speed of Analog-to-Digital (A/D) converter can be increased due to the use of ultra-high-speed RTD digitizer. The RTD digitizer is comprised of two RTD circuits, and its switching speed is independent of the value of the positive differential resistance region and is only dependent of the value of the negative differential resistance. The switching speed through the negative differential resistance region has been shown to be very fast by many people. In addition, the folding characteristics of RTD devices can greatly reduce the circuit complexity of the folding type of A/D converter which is a high speed structure alternative to the flash type A/D converter. The speed performance of the RTD based A/D converter is analyzed by theoretical derivation and simulation. The extrinsic hysteresis and current-voltage characteristics of the multi-well, vertically-integrated, resonant-tunneling diode is analyzed. This analysis results in a device model which is supported by experimental results. By using a piecewise linear technique, the I-V curve of the multi-peaked RTD is divided into several regions and each region is modeled individually. By incorporating the switch model of SPICE3, the individual models are combined to form a large-signal RTD model. This large-signal model is used to simulate the performance of a 4-bit A/D converter digitizing high frequency input with digital output changing at a 60GHz rate. A breadboard circuit is constructed and tested for a 2-bit A/D converter using discrete 2-peak InGaAs/InAlAs vertically integrated RTDs. The experimental results confirmed that the basic concept for an A/D converter based on the RTD works. Results from the experimental demonstration and circuit simulation are discussed.