Microwave analog-to-digital converters for broadband communications

Summary form only given. Microwave A/D and D/A converters enable digital RF systems where virtually all information is processed or generated by direct digital means. A complete receiver link can consist of a sensor (e.g. antenna or photodetector), an N-bit A/D converter, and a digital signal processor. A complete transmitter can be built using the appropriate actuator (antenna or laser), an N-bit D/A converter and a digital waveform synthesizer. Future radar, electronic warfare, and communication systems will exploit this all-digital approach to increase the performance and flexibility while lowering the cost. We describe how quantum switching devices can be used to build A/D converters with ultimate sampling rates well above 100 GHz. Resonant tunneling diodes (RTDs) are integrated with heterojunction field effect or bipolar transistors to sample, quantize, encode, demodulate, and filter broadband analog signals. Single-ended and differential circuits are discussed and compared for power consumption, area, and speed. Comparisons are made between RTD/FET and FET-only A/D functions. Results are shown for A/D quantizers that have sub-millivolt threshold sensitivity at 10 GHz sampling rates.