| Wireless applications would be less expensive, more flexible, and more robust if they had more digital and less analog circuitry. The problem is implementing digital signal processing at radio frequencies. Conventional data converters (ADCs and DACs) and digital circuits are simply not fast enough. However, superconductors can provide ultra fast mixed signal and digital circuits with the linearity and dynamic range required for true direct, digital-RF processing. In fact, a US Navy laboratory is now evaluating the world’s first complete prototype digital RF receiver capable of direct digitization from DC to 2 GHz. .
The superconducting circuits are digital ICs based on Josephson junctions and “rapid-single-flux-quantum” logic (RSFQ), where switching speeds up to 750 GHz have been demonstrated. Medium scale ICs operate at speeds up to 200 GHz, enabling true digital-RF architecture. This permits direct conversion between analog RF and digital baseband signals, replacing frequency and protocol-specific analog hardware with flexible digital processors. Data conversion in high frequency wireless applications at frequencies up to 50 GHz will soon become practical.
Hypres recently delivered a HF-UHF All Digital RF Receiver (ADR) prototype to ONR. Testing of this ADR has demonstrated the superior performance of superconducting ICs in cryocooled systems. Specific tests and measurements evaluated and passed included:
• compatibility evaluations with standard Army SINCGARS radios and waveforms;
• testing of selected HF/VHF signals; and,
• Signal-to-Noise and Spurious Free Dynamic Range measurements.
HYPRES demonstrated high sampling-speed (20 Gsamples/s) and linearity (>110 dB spur-free dynamic range) within the HF-UHF All Digital RF Receiver (ADR) consisting of a superconductor analog-to-digital converters (ADCs), digital down-converters and ultra fast (20 GHz) digital filters.
The next generation of the ADR currently under development will work at 40 GHz clock. Similar developments are underway for C-Band and X-band ADRs. Future circuits are expected to advance to higher sampling rates (100 to 200 Gsamples/s) and more complex specialized DSP functions. The extreme high-speed logic and improved sensitivity of superconducting electronics will greatly improve the performance of high frequency wireless applications in the near future.
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