  We present a sub-Nyquist analog-to-digital converter of wideband inputs. Our
circuit realizes the recently proposed modulated wideband converter, which is a
flexible platform for sampling signals according to their actual bandwidth
occupation. The theoretical work enables, for example, a sub-Nyquist wideband
receiver, which has no prior information on the transmitter carrier positions.
Our design supports input signals with 2 GHz Nyquist rate and 120 MHz spectrum
occupancy, with arbitrary transmission frequencies. The sampling rate is as low
as 280 MHz. To the best of our knowledge, this is the first reported wideband
hardware for sub-Nyquist conversion. Furthermore, the modular design is proven
to compete with state-of-the-art Nyquist ADCs in terms of resolution bits and
full-scale range. We describe the various circuit design considerations, with
an emphasis on the nonordinary challenges the converter introduces: mixing a
signal with a multiple set of sinusoids, rather than a single local oscillator,
and generation of highly-transient periodic waveforms, with transient intervals
on the order of the Nyquist rate. A series of hardware experiments validates
the design and demonstrate sub-Nyquist sampling.
