Okkim Atnarivik
Guest
Wed May 18, 2011 11:23 pm
In sci.electronics.design Spehro Pefhany <speffSNIP_at_interlogdotyou.knowwhat> wrote:
: Did you end up using the SiGe option?
SiGe is the obvious choice for the cryogenic LNA at the 'warm' 110K
end of the cable, but its efficiency when operated class-A causes too
much dissipation at 4K. Making a class-B or class-D amplifier out
of packaged SiGe discretes is probably too tedious, especially dealing
with the stability issues and the dissipation budget when there are many
active devices per an amp. Custom transistors or an ASIC would be
conceivable, e.g. SiGe devices from the AMS SiGe BiCMOS process (available
via MOSIS or Europractice) are known to function at 4K. Weinreb and his
colleagues have recently fabbed cryogenic SiGe amps for the SKA using
(I think) IBM SiGe process. A SiGe ASIC is probably a slow
path, however, which is likely to take several design iterations. We
have a superconducting foundry in-house, hence I'd prefer to keep the
control in our own hands and try to manage with SQUID-related devices.
Regards,
Mikko
Okkim Atnarivik
Guest
Wed May 18, 2011 11:33 pm
In sci.electronics.design George Herold <gherold_at_teachspin.com> wrote:
: By EMI I assume you are talking about 'cr_at_p' leaking in through the
: cable shield.
: This is probably silly, but could an active shield driven from the
: high temperature end help with EMI? I was playing around with a
: driven shield last year to help get the signal out. (reduce cable
: capacitance) So shield was driven by the signal. To shield from EMI
We did consider guarding, but that becomes tough at high frequencies
where the cable represents a (small) fraction of the wavelengths. Already a
small phase shift between the EMI and the guard signal would cause
untolerably strong coupling.
Regards,
Mikko
