Specifications

13
The Agilent 8510C has the capability to make
measurements of amplifiers operating in their non-
linear region. A swept-frequency gain compression
measurement locates the frequency at which the
1 dB gain compression first occurs. A swept-power
gain compression measurement shows the reduc-
tion in gain at a single frequency as a power ramp
is applied to the AUT.
Swept-frequency gain compression
A measurement of swept-frequency gain compres-
sion locates the frequency at which the 1 dB gain
compression first occurs. The swept-frequency gain
compression is determined by normalizing to the
small signal gain and by observing compression as
the 1 dB drop from the reference line as input
power is increased. The swept-frequency gain com-
pression and corresponding output power (P
1dB
)
can be displayed simultaneously on the 8510C net-
work analyzer.
1. Perform an absolute output power calibration
and measurement (as previously described).
2. Channel 1 should already be set up for an
absolute power measurement (with correction on).
Set up channel 2 for an S
21
gain measurement.
Turn on a dual channel split display.
[CH 2] [S21]
[LOG MAG]
[DISPLAY] {DISPLAY MODE}
{DUAL CHAN SPLIT}
3. Connect the AUT and apply bias, if necessary.
4. Normalize the display to the small signal gain.
[DISPLAY] {DATA AND MEMORIES}
{DATA->MEMORY}
{Math (/)}
A flat line at 0 dB should now be displayed on
channel 2.
5. Set a scale of 0.5 dB/division and a reference
value of 0 dB to allow easy viewing of a 1 dB drop
from the small signal gain.
6. Increase the source power level until the trace
drops by 1 dB at some frequency. A marker can
then be used to read the exact frequency where the
1 dB compression first occurs. Care should be
taken when increasing the source power so that
the input power limitation of the AUT is not
exceeded.
STIMULUS [MENU]
{POWER MENU} {POWER SOURCE 1}
Use knob or arrow keys to increase power.
[MARKER]
{MARKER 1}
7. Set the source power on channel 1 to the same
value as for channel 2. The channel 1 marker dis-
plays the actual output power of the amplifier (in
dBm) at the 1 dB gain compression point. In this
example, the 1 dB gain compression first occurs at
26.255 GHz at an output power level of 16.19 dBm.
Nonlinear measurements
Figure 12. Swept-frequency gain compression measurement