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loss should be approximately equal
to the fixed attenuation value
being removed from the system.
Further, as discussed earlier, adding
equalizers prior to gain stages creates
dispersion in limiting dynamic range
vs frequency. To minimize this effect,
substitute the minimum number of
equalizers possible.
Finally, equalizers can be added to the
device output. Output equalization
reduces output power, but will
not create limiting dynamic range
dispersion. Output equalization does
create a slightly positive output power
slope, but this slope is offset by high
frequency package and connector
loss. A completed four stage limiting
amplifier layout is illustrated in Figure
9.
Figure 10 illustrates the output power
vs temperature simulation result for
ADI’s HMC7891. The final design
achieves 40 dB limiting dynamic
range and has a simulated worst case
output power variation of 3 dB under
all operating conditions.
ADI Limiting Amplifier
Test Results
Test results for the HMC7891 are
illustrated in Figures 11–18. Results
demonstrate the design was able to
achieve 47 dB gain with a saturated
output power of 13 dBm. The
amplifier’s input power range is -30 to
10 dBm, for a limiting dynamic range
of 40 dB. The unit was tested over an
operational temperature range of -40
to 85°C. A photograph of the HMC7891
is shown in Figure 19. Though the
HMC7891 was primarily designed
as a limiting amplifier the small size
and superior RF performance enable
utility in various applications including
use as a frequency tripler or as an
LO amplifier. The design technique
described herein can be used for
future limiting amplifier designs with
modifications to spec requirement
such as frequency, output power,
gain, NF, or limiting dynamic range.
“Thermopad” is a registered
trademark of EMC Technology, Inc.
New-Tech Magazine Europe l 57