China Electronics Technology Instruments AV3672 Series, User Manual

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Appendix
Appendix 5 Amplifier Gain Compression Measurement
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The linear zone and compression zone are separated in the two sweep methods. The signals within the same
frequency range should be swept at different power levels in the repeated sweep. The first half of sweep aims to
measure the DUT return of X-axis power level. The second half of sweep aims to measure the corresponding start-
stop power range of the DUT at the compression power level. At the beginning of the second half, the power level
will increase if the return or X-axis value increases. The specific time is set as the DUT response to power level
changes. The input power must not be reduced to the minimum value in safety sweep. Instead, safety sweep aims to
prevent DUT from being greatly influenced by power changes.
2) Linear gain compression
After the reference gain is measured in the linear input power zone, DUT can be pushed to the high-power
compression level for repeated measurement. The power is increased or decreased according to the DUT power
level in subsequent measurements to reach the expected compression level. Generally, the appropriate algorithm
can be obtained after the third repeated sweep, so as to draw the curve and accurately find the compression point.
Attention
Influence of power sweep on measurement results
DUI may change greatly in different sweep processes. The influence can be reduced by enabling safety sweep or
carefully selecting the appropriate settings.
1) Maximum gain compression
The maximum gain of each frequency point will be saved to calculate the compression point. In the intelligent
sweep mode, additional repeated sweep of each frequency point will not be done to search the possible maximum
gain of the amplifier.
2) Compression in saturated state
The external maximum gain of each frequency point will be saved to calculate the compression point. In the
intelligent sweep mode, additional repeated sweep of each frequency point will not be done to search the possible
maximum gain of the amplifier.
5.2.7 Factors Related to Measurement Accuracy
The analyzer must have high power to drive the amplifier into the saturated zone. If the power level of the signal
source of the analyzer does not conform to the requirements, a preamplifier should be set in front of the tested
amplifier to improve the power level. The applied preamplifier must be included in calibration. If necessary, the
output of the amplifier should be fully attenuated. Too high output power may cause the following results.
a) The output power is higher than the input compression level of the receiver of the analyzer, which may lead to
inaccurate measurement results.
b) The analyzer receiver may be damaged.
The output power of the amplifier can be attenuated by the attenuator or coupler. As part of the test, the influence
of the attenuator or coupler must be taken into consideration. Proper error correction can help to reduce the
influence of such accessories.
a) The frequency response is a main error source of gain compression measurement. The error can be reduced
significantly by means of through type response calibration.
b) The amplifier has different response values corresponding to temperature differences. The test must be done at
the working temperature of the amplifier.
c) The dynamic range and accuracy can be improved by reducing the intermediate frequency bandwidth or using
the measurement averaging function, but at the sacrifice of measurement velocity.
5.3 Steps of Gain Compression Measurement
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Resetting of analyzer
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Enabling of gain compression measurement ····································································· 418