Abstract
By linking the unique capabilities of photonic devices with the
signal processing power of electronics, photonically sampled
analog-to-digital (A/D) conversion systems have demonstrated the potential
for superior performance over all-electrical A/D conversion systems. We
adopt a photonic A/D conversion scheme using low-temperature (LT)-grown
GaAs metal-semiconductor-metal (MSM) photoconductive switches integrated
with Si-CMOS A/D converters. The large bandwidth of the LT GaAs switches
and the low timing jitter and short width of mode-locked laser pulses are
combined to accurately sample input frequencies up to several tens of
gigahertz. CMOS A/D converters perform back-end digitization, and
time-interleaving is used to increase the total sampling rate of the
system. In this paper, we outline the development of this system,from
optimization of the LT GaAs material, speed and responsivity measurements
of the switches, bandwidth and linearity characterization of the
first-stage optoelectronic sample-and-hold, to integration of the switches
with CMOS chips. As a final proof-of-principle demonstration, a
two-channel system was fabricated with LT GaAs MSM switches flip-chip
bonded to CMOS A/D converters. When operated at an aggregate sampling rate
of 160 megasamples/s, the prototype system exhibits ~3.5 effective number
of bits (ENOB) of resolution for input signals up to 40 GHz.
© 2003 IEEE
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