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DDS Amp Analysis
K8IQY examines the gain-bandwidth performance of the DDS Amp to determine optimal gain gettings |
About the
AmQRP Club |
An
LT1252 amplifier used for DDS post-amplification service was evaluated using an
Advantest R3361A spectrum analyzer. The
LT1252 DDS amplifier was supplied by George Heron, N2APB of the AmQRP
organization.
The amplifier was
evaluated by driving it at a signal level of -10 dBm, using the tracking
generator in the R3361A. Its output
was fed to the spectrum analyzer and the frequency response was measured from 1
MHz to 100 MHz. A comparable data plot was produced using the identical setup,
but with a LT1253 dual amplifier. The data differences between these two
amplifiers are show below.
Data Comparison:
Frequency
(Mhz)
LT1252 Output (dB)
LT1253 Output (dB)
Difference (dB)
1
3.1
8.7
5.6
10
2.7
8.6
5.9
20
1.9
8.4
6.5
30
0.7
8.2
7.5
Freq
1-100 MHz Diff:
2.4
0.5
Note
that the LT1253 amplifier was set up to provide approximately 19 dB of power
gain at 1 MHz, whereas the LT1252 amplifier as evaluated was designed to provide
approximately 13 dB of gain at the same frequency. The feedback resistor pair in
the LT1253 can be adjusted to provide the same 13 dB gain level as the LT1252
amplifier, while improving the higher frequency response (less loss at 30 MHz).
In fact, the feedback scheme used in the LT1253 amplifier was optimized for
added gain with some slight degradation of 30 MHz performance.
The respective Bode plots of the LT1252 and LT1253 amplifiers are shown below ...
Jim Kortge, K8IQY
Material and concepts
presented on the AmQRP website is Copyright 2005 by the American QRP Club,
Inc.
These pages are designed and maintained by George Heron, N2APB
(n2apb_at_amqrp.org)
Page last updated: May 2, 2005