ALMA Memo #410
Designing and Prototyping of 2-4 GHz Bandpass SiGe Digitizers and
Associated Test Equipment for the ALMA Project. I
Alain Baudry 1, David Deschans 2,1, Jean-Baptiste Begueret 2, Yann Deval 2,
Pascal Fouillat 2, Guy Montignac 1, Olivier Gentaz 3, Marc Torres 3
1 Observatoire de Bordeaux, BP 89 33270, Floirac, France
2 Laboratoire IXL, Université de Bordeaux, 351 cours de la Libération, 33405 Talence, France
3 Université de Grenoble, IRAM, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France
2002/02/20
Keywords: fast digitizers, demultiplexers, digitizer test equipment
In this first paper we describe the approach followed to design and
experimentally test the high speed and broad band analog-to-digital
converters (ADC's or digitizers) required for the ALMA project. Our
prototypes are based on monolithic digitizers implemented in a BiCMOS 0.35
or 0.25 µm SiGe process with 3 or 8 quantization levels and 4 giga samples
per second rate for an input signal from 2 to 4 GHz under full Nyquist
condition. We have adopted a conventional flash converter architecture to
design three different 2-bit digitizers and one 3-bit digitizer. The
experimental results obtained with our first 2-bit digitizer ASIC show that
sinusoidal input signals are properly sampled for clock rates up to 4.9
GHz. The design details and high dynamic range tests of our ADC's will be
reported in forthcoming papers. A specific digitizer test equipment
providing the auto-correlation and spectral analysis of the digitized
signal has been developed to characterize our designs and provide the
necessary feedback to the ASIC design team. It includes a broad band noise
generator, a demultiplexing unit following the digitizer under test, a
16-lag auto-correlator, and FFT and display units. This equipment will
also play a major role at the pre-production stage and for
qualification/acceptance at the production stage. We suggest that the
demultiplexing scheme developed for the digitizer test equipment could be
used as a basis for multi-bit synchronization of the demultiplexed signal
in front of the ALMA fiber optic transmitter system.
View a pdf version of ALMA Memo #410.
Download a zipped postscript version of ALMA Memo #410.