NF FRA5087, Instruction Manual

Page: 98 / 194

4.9 Amplitude compression
FRA5087
4-24
4.9 Amplitude compression
The oscillator output amplitude level is so controlled that the amplitude level of the DUT (device
under test) is kept at a certain level. This is to prevent saturation of, or damages to, the DUT,
when the DUT amplitude response has a high peak level.
OS
C
CH1 CH2
FRA5087
Device under
test (DUT)
f
G
ain
The amplitude at this point
should be kept at a certain level.
Fig. 4-15 Amplitude compression
The amplitude control is done in the following way:
1) Measurement is done once, with the current setting value of the oscillator output voltage.
2) Comparison is made between the measurement data and the compression level setting. If
the comparison result (i.e., difference) is within the permissible range, the measurement at
the frequency is completed.
3) If the difference is beyond the permissible range, the oscillator output voltage is controlled
according to the DUT gain, which is obtained from the measurement data.
4) Measurement is made again and the measurement data is again compared with the
compression level setting to find the difference. If the difference is still beyond the
permissible range, repeat the measurement and comparison. If the measurement and
comparison are repeated for the preset number of times and still the difference is beyond
the permissible range, the measurement at this frequency terminates with an error message.
5)
The measurement data will be output.
The FRA5087 has a provision that the maximum oscillator output level can be set so that it will
not exceed the maximum permissible DUT input level, when the oscillator output voltage is
controlled according to the step
3)
above. The FRA5087 also has a provision that the correction
voltage factor (correction voltage = the difference between the current output voltage and the next
output voltage) can be changed so that the measurement system can be applied to such DUTs that
do not like steep input voltage change or such DUTs whose amplification gain varies according to
the operating level.
DFT
DFT
CH1
CH2
Display processing, etc.
[ R E F L E V E L ]
[ R E F C H A N N E L ]
[ C O R R E C T I O N
F A C T O R ]
+
Limiter
[ O U T P U T L I M I T ]
Amplitude control
OSC
-
+
+
+
+
Fig. 4-16 Principle of amplitude compression