flysnows
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bandpass delta sigma
Thesis: A Superconducting Bandpass Delta-Sigma Modulator for Direct Analog-to-Digital Conversion of Microwave Radio
by John Francis Bulzacchelli
Massachusetts Institute of Technology,2003
This thesis examines the potential of superconducting technology for realizing RF analogto-digital converters (ADCs) with improved performance. A bandpass delta-sigma (ΔΣ) modulator is an attractive architecture for digitizing narrowband signals with high linearity and a large signal-to-noise ratio (SNR). The design of a superconducting bandpass ΔΣ modulator presented here exploits several advantages of superconducting electronics: the high quality factor of resonators, the high sampling rates of comparators realized with Josephson junctions, natural quantization of voltage pulses, and high circuit sensitivity. Demonstration of a superconducting circuit operating at clock rates in the tens of GHz is often hindered by the difficulty of high speed interfacing with room-temperature test equipment. In this work, a test chip with integrated acquisition memory is used to simplify high speed testing in a cryogenic environment. The small size (256 bits) of the on-chip memory severely limits the frequency resolution of spectra based on standard fast Fourier transforms. Higher resolution spectra are obtained by “segmented correlation”, a new method for testing ADCs. Two different techniques have been found for clocking the superconducting modulator at frequencies in the tens of GHz. In the first approach, an optical clocking technique was developed, in which picosecond laser pulses are delivered via optical fiber
to an on-chip metal-semiconductor-metal (MSM) photodiode, whose output current pulses trigger the Josephson circuitry. In the second approach, the superconducting modulator is clocked by an on-chip Josephson oscillator.
Thesis: A Superconducting Bandpass Delta-Sigma Modulator for Direct Analog-to-Digital Conversion of Microwave Radio
by John Francis Bulzacchelli
Massachusetts Institute of Technology,2003
This thesis examines the potential of superconducting technology for realizing RF analogto-digital converters (ADCs) with improved performance. A bandpass delta-sigma (ΔΣ) modulator is an attractive architecture for digitizing narrowband signals with high linearity and a large signal-to-noise ratio (SNR). The design of a superconducting bandpass ΔΣ modulator presented here exploits several advantages of superconducting electronics: the high quality factor of resonators, the high sampling rates of comparators realized with Josephson junctions, natural quantization of voltage pulses, and high circuit sensitivity. Demonstration of a superconducting circuit operating at clock rates in the tens of GHz is often hindered by the difficulty of high speed interfacing with room-temperature test equipment. In this work, a test chip with integrated acquisition memory is used to simplify high speed testing in a cryogenic environment. The small size (256 bits) of the on-chip memory severely limits the frequency resolution of spectra based on standard fast Fourier transforms. Higher resolution spectra are obtained by “segmented correlation”, a new method for testing ADCs. Two different techniques have been found for clocking the superconducting modulator at frequencies in the tens of GHz. In the first approach, an optical clocking technique was developed, in which picosecond laser pulses are delivered via optical fiber
to an on-chip metal-semiconductor-metal (MSM) photodiode, whose output current pulses trigger the Josephson circuitry. In the second approach, the superconducting modulator is clocked by an on-chip Josephson oscillator.
