EDNE February 2013 - (Page 16)
A mo
insight intonthly
T&M techn the latest
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the pages logy from
Measurem of Test &
(www.tmw ent World
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Test & Measurement
World is the leading
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engineers and managers in the electronics testing industry.
®
An economy low-noise
instrumentation preamp
Using a pre-amp ahead of a measurement instrument such as a spectrum analyzer,
when low-level signals are being explored, can lower noise floor and reveal
more signal detail. The evaluation platform for a new wideband amplifier IC
offers a low-cost option.
®
Kenneth Wyatt, in Test & Measurement World’s “EMC blog”
L
ast year Mini-Circuits developed a (really!) low-noise,
broad band, preamp (model PSA4-5043+) for use as a
front-end amplifier for mobile telecom applications,
such as GSM, CDMA, LTE and WiMax. However, it would
also be ideal to act as a pre-amplifier for spectrum analyzers:
the low-noise feature would lower the effective noise figure of
the analyzer, allowing you to see low-level signals better. This
would not only be useful for amplifying near-field or current
probe outputs, but would work well to boost the antenna
output in semi-anechoic chambers - especially if there is a
long run of coax cable. The PSA4-5043 costs about $2.50
in quantities of 20; however, rather than ordering the device
itself, note that Mini-Circuits sells the amplifier already built
into a high-quality test board and brass housing (model #
TB-653+) for just $59.95 in single quantities. It’s orderable
right off their web site.
The MMIC amplifier is based on E-PHEMT technology
and is specified from 50 MHz to 4 GHz with an amazing
noise figure of 0.73 to 1.44 within that frequency range. The
output power at 1dB compression is about 16 to 20 dB and
the third-order intercept ranges from 28 to 31 dB. It should
operate moderately well in high dynamic range environments. It’s really quite good for a single four-legged SOT-343
device. In addition, it’s also rated Class 1B (HBM) at 500 to
<1000V for ESD.
I tried measuring the preamp using my Rigol DSA815TG
spectrum analyzer (with tracking generator) and found the
gain to vary from 25 to 15 dB from 1 to 1,500 MHz (the upper
limit of the analyzer), just as the data sheet specifies. Note
that, despite Mini-Circuit’s spec of 50 MHz for the lower
limit, I found it would amplify all the way down to 5 MHz.
To power the preamp, I took a spare USB cable and cut off
the larger end, leaving enough to
reach the USB port on the analyzer. On my cable, the +5V was
the red wire, and black was the
return. Be sure to verify your cable
using a volt meter before connecting to the preamp.
I adjusted the tracking generator output to -20 dBm, so the
preamp wouldn’t saturate. I also
changed the vertical scale from 10
dB to 5 dB per division, so I could
observe gain changes more easily.
After normalizing the analyzer, I
adjusted the offset so the positive
gain would display properly on the
screen.
You’ll want to print out this
gain versus frequency plot (or save
as a calibration table) in order to
Figure 1. The gain of the preamp from 1 to 1,500 MHz (the limit of the analyzer).
provide a calibration factor for
It varies from 25 to 15 dB as per the Mini-Circuits data sheet.
certification testing or for accu-
16 EDN EUROPE | February 2013
www.edn-europe.com
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Table of Contents for the Digital Edition of EDNE February 2013
Cover
Digi-Key
Contents
RS Components
Microchip
Agilent Technologies
Masthead
EDN.comment
Digi-Key
Pulse
Maxim Integrated
Renesas
Signal Integrity
Mesago SMT 2013
Test & Measurement World
Rohde & Schwarz
Mesago PCIM 2013
Mechatronics in Design
Hot technologies: trends to watch in 2013
EPN
Hot 100 products of 2012
Add LED intelligence to improve light quality, efficiency, and cost
Design Ideas
EDNE
IAN
Product roundup
Tales from the Cube
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