Updated July 5,
here to go to our main page on attenuators
here to go to our page on variable attenuators
New for June 2011! This
topic was suggested by Chin-Leong, who was mentored by Ray Waugh.
At Chin-Leong's request, we have placed Ray Waugh in the Microwave
Hall of Fame!
Ray Waugh's attenuator is a PIN
diode network that provides voltage-variable attenuation over a
broad bandwidth. By replacing the series resistor in the Pi network
with two diodes, three benefits result:
- First, since the maximum isolation
of the network is set by the capacitive reactance of the series
diode(s), the use of two diodes in place of one will increase
the maximum attenuation or double the upper frequency limit for
a given value of attenuation.
- The twin diodes which occupy
the position of the series resistor are physically set up 180°
out of phase, resulting in the cancellation of even order distortion
- The resulting attenuator network
is symmetrical and the bias network is substantially simplified.
Below is the PIN diode attenuator,
before Waugh. Note the excessively-complicated bias scheme, and
the asymmetry. You can also learn more from page 152 of Ulrich Rohde's
online book, RF/Microwave Circuit Design for Wireless Applications.
attenuator using PIN diodes prior to Waugh
Here is a schematic of Waugh's
You can learn all about this
network from Agilent's App-Note AN1048, A Low-Cost Surface Mount
Attenuator. You can easily find this through a Google
search. The Agilent semiconductor division has since become
Avago. AN1048 is where we cribbed the two schematics from, we hope
Agilent (or Avago) doesn't mind, but we suspect that Ray Waugh won't!
Waugh's attenuator is also described
Waugh, R. W., "A Low
Cost Surface Surface Mount PIN Diode PI Attenuator,"
Microwave Journal, vol. 35, no. 5, May 1992, pp 280-284.
Ray's biography is from
his paper which appeared in Applied Microwave & Wireless:
Raymond W. Waugh is
diode applications engineer for the Wireless Semiconductor
Division of Hewlett-Packard Company. He is a Senior Member
of the IEEE, a member of the Microwave Theory and Techniques
Society, and is on the editorial board for IEEE Transactions.
He is also a member of SAE.
Waugh obtained his BSEE
degree from the University of Michigan in 1962 and his MSEE
from UCLA in 1968. He has written or co-written approximately
20 papers, and has conducted diode design seminars in Europe,
Asia and the United States.
In addition, we have learned
that Waugh was anti-patent, so his novel attenuator was adopted
quickly. His four-diode
attenuator is the most ubiquitous wideband attenuator configuration
in the industry.
Waugh's configuration has become
the de-facto industry standard for multi-octave, compact, high linearity
attenuator. His invention solved the asymmetrical drive requirement
of the previous three-diode
attenuator and also improved linearity by distortion self-cancelling
in the anti-series PIN diode arm.
Waugh served the society in the
Editorial Board of MTT Transactions 1999-2000.