Search

Research was conducted to design and simulate two-loop Delta-Epsilon modulators capable of greater than 100 dB of signal-to-noise ratio for a 10 MHz input bandwidth. Each modulator was capable of operating at 10 GHz. Current state-of-the-art analog-to-digital converters have approximately 85 dB of dynamic range at 10 MHz input bandwidth. The modulators offer the opportunity for increased resolution.

The application of thin-film transformers to microwave circuits is described. A low-frequency lumped-element analysis of the devices including calculations of their bandwidth was conducted. An alternative model for the transformer where each part of the patterned circuit is treated as a distributed element is presented. Numerical simulations based on the distributed model were in excellent agreement with data taken on actual devices.

Circuits for receiving and transmitting bits generated by Single Flux Quantum circuits have been developed using shunted Nb-AlOx-Nb junctions. A series array of dc SQUIDs driven into the voltage state was used as a transmitter and inductively coupled with the receiver circuit. The transmitter generated a maximum peak-to-peak amplitude of 296 micro V at a clock rate of 2.5 GHz and 187 micro V at 5 GHz.

Three types of high-transition-temperature magnetometers are developed with the use of a YBa2Cu3O7-x-SrTiO3-YBa2Cu3O7-x multilayer process. These are multiturn flux transformers combined with single layer direct current superconducting quantum interference devices (SQUIDs) in flip-chip arrangements, multiturn flux transformers integrated with dc SQUIDs and multiloop magnetometers.

The feasibility of using a high-critical temperature superconducting quantum interference device (SQUID) in obtaining high frequency magnetic microscopic images is evaluated through experimental procedures. A SQUID-based microscope is designed and employed in imaging subsurface defects in metal structures at frequencies ranging from zero to 200 GHz. Results show that the SQUID-based microscope is a very useful tool for nondestructive testing of metals.

The operating characteristics of yttrium barium copper oxide superconducting quantum interference devices (SQUIDs) fabricated on a single SrTiO3 bicrystal substrate were studied. The SQUIDs' current-voltage properties were measured in a liquid nitrogen environment under the presence of an ambient magnetic field. An electronic modulation scheme was then employed to reduce the SQUIDs' white noise emission to a useful level. Results reveal that the use of the current reversal scheme decreased the white noise level by at least two orders of magnitude.