Product specifications

Compression vs. Frequency Measurements in Pulse Mode

Gain Compression (commonly specified as input/output power at 1 dB com-

pression point: IP1dB/OP1dB) is a very popular amplifier characteristic. It is

measured and calculated from either swept-power gain (S21) or amplifier output

power at a single frequency point. Often this is repeated at many frequency

points to characterize the amplifier compression point over its operating fre-

quency range (Figure 28). The PNA-X offers a gain compression application

(GCA) option that provides fast and accurate compression measurements versus

frequency with a very simple setup. It is important in this measurement that

the compression points are calculated from accurate input power with gain or

output power measurements. The GCA corrects power/receiver and mismatch

errors, providing the highest level of accuracy for compression measurements.

When the amplifiers are in pulse mode, these error corrections need to be kept

valid in order to take advantage of the accurate measurements with GCA. In

this section, we will discuss amplifier’s compression versus frequency measure-

ments under pulse operation using the GCA option and wideband detection

technique (narrowband pulse is not available in PNA-X application measurement

classes). But this technique for setting up a pulsed-RF measurement is also

applied to setting up a pulsed-RF mixer/converter compression measurement in

a Gain Compression Converters (GCX) measurement class.

The measurement setup and calibration procedure is similar to the pulsed

S-parameter measurement setup. Measuring stimulus level correctly is cru-

cial for accurate compression measurements, which requires GCA calibration

remains enabled with pulsed stimulus. Use receiver leveling to level the pulsed

stimulus, then GCA calibration for accurate compression versus frequency

measurements. Fortunately, R1 receiver used for the source leveling is cali-

brated during the GCA calibration (B receiver is calibrated as well); therefore

no additional calibration for the receiver leveling is needed. Note, measure-

ments with such wide IF bandwidth become noisy thus adding averaging is

recommended. A wider IF bandwidth may cause misalignment between the

data acquisition and pulses resulting in a noisy trace. Adding 300 ns or more

delay to the Pulse 0 (the pulse for data acquisition) solves this problem as

explained earlier in the PNA-X pulse system delay section. Once the GCA and

pulse setup is completed, turn off the pulse modulation for calibration. The

GCA calibration wizard guides you through the steps based on the measure-

ment setup. Then the pulse modulation drive can be switched back to the

pulse generator and the R1 receiver is ready for leveling pulsed stimulus.

Figure 28. Compression measurements vs. frequency

Gain

Frequency

Compression

Point