[asac] [almanews] Recent ALMA Memos

[Carolyn White]

ALMA Memo # 510

The ALMA Digitizer (DG) Demultiplexer :
Design, Performances in DG Assembly and Production Acceptance Tests

Cyril Recoquillon
Alain Baudry
Jean-Baptiste Begueret
Stephane Gauffre
Guy Montignac

2004-12-13

Keywords:Demultiplexer/Deserializer, SiGe technology, High-speed digital
circuit, Self-test, Digitizer assembly

Abstract: A high frequency, low power 1:16 deserializer has been
developed using the 0.25?m BiCMOS SiGe technology from ST
Microelectronics to meet the ALMA project requirements. The input shift
register is clocked at 4 GHz and the output data are transferred at 250
MHz. Nominal operation has been observed up to 8 GHz. With 2.5 V supply,
the circuit dissipates around 650 mW an especially low value compared to
existing similar circuits. The chip is available in an industrial
package and exhibits low thermal resistance (about 25 ?C/W) thus
implying long lifetime as required for the ALMA project. Functional
tests including those performed with a self-test block embedded in the
deserializer are briefly described. Our deserializer is integrated in a
prototype ALMA Digitizer assembly which includes a 3-bit (8-level), 4
GS/s sampler developed with the same SiGe process. Based on Digitizer
state counts measurements, Allan variance tests and long term operation
in the laboratory environment, we conclude that the prototype Digitizer
assembly is operational. The deserializer chip has reached the final
production stage after static and dynamic qualification tests have been
performed on a first restricted number of production chips.

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ALMA Memo # 511

Cycle-Slip-Free Fiber Length Stabilization System Using a Digital Phase
and Frequency Discriminator

Yohei Sato, Mitsuru Musha, Ken'ichi Nakagawa, Ken-ichi Ueda, Akitoshi
Ueda, Masato Ishiguro 

2004-12-15

Abstract: We have developed a fiber length stabilization system (FLSS)
for the photonic distribution of LO signals by using a digital phase and
frequency discriminator (DPFD). Compared with a conventional analog
double-balanced mixer (DBM) or a phase sensitive detector with an XOR
gate (PSD), the DPFD has wider linear discrimination range by more than
1000 times, which enables cycle-slip-free FLSS. Moreover, it makes
possible to stabilize the length of the fiber that is longer than the
coherent length of the light source used in FLSS. 

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ALMA Memo # 513

Design and Simulation of a Waveguide Load for ALMA-band 9

F. P. Mena
A. M. Baryshev 

2005-01-07

Abstract:An important element of any waveguide-based dispositive is the
termination or load. At relatively large wavelengths the idea is to make
them as compact as possible and usually contained inside of the
waveguide. However, as the working frequency increases, the involved
dimensions make more difficult such approach. In this memo, we describe
a relatively simple waveguide load which is appropriate when the
waveguide dimensions are prohibitory small. The load described here is
rather large compared with the waveguide making it relatively easy to
realize at small dimensions. Moreover, from the results of a simulation
it is shown that besides its simplicity it can have a reflectivity as
low as -40 dB if the appropriate material is used. 

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