| Research Abstract |
For the purpose of achieving analog-to-digital converters (ADCs) that are able to convert microwave signals to digital ones directly, we have investigated high-speed, high-resolution ADCs using resonant-tunneling diodes (RTDs).
1.Flash ADC : We proposed novel ultrahigh-speed functional circuits that consist of RTDs and high-electronmobility transistors (HEMTs), and designed flash ABCs by applying the circuits not only to multi-level quantizers used as the front end but also to the encoder. This made the ADC circuit configuration quite compact (1/2 compared with conventional one). SPICE simulation showed that the power consumption was much reduced to a value as low as 0.3W (about half that required in conventional ADCs) for a 4-bit 10-GHz operation. Also we proposed a 5-bit flash ADO using the latched nature of RTD-based circuits as a pipelined manner, which resulted in a possible 4.6-ENOB, 10-GHz operation. (ENOB : effective number of bit)
2.DeltaSigma ADCs : Focusing continuous-time, bandpass delta-sigma ABCs that are suitable for wireless communication applications, we investigated ones including the flash ADCs using RTDs described above, and showed a possible delta-sigma ultrahigh-speed, high-resolution operation by adjusting the feedback parameter in accordance with the RTD duty ratio. We also designed a continuous-time bandpass delta-sigma modulator (DSMD assuming InP-based HEMT technology, and obtained simulation results that showed 8-bit 4-GHz operation with a center frequency of 0.5 GHz. Furthermore, we proposed a cascade bandpass DSM with the multi-bit DEM scheme, which suggested 16-bit operations. (DEM : dynamic element matching)
Although our investigation has been mainly focused on fundamental building circuit blocks, characteristics of each circuit are satisfactory and encouraging. Thus, it strongly suggests that by integrating such elements, we can certainly obtain the ABC performances that were predicted at the beginning of this project.
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