Front-panel operation 13
threshold to initiate the integration process. Once the trigger level is selected, the
output is turned on and the pulsed load measurement is operational, the 2308 can
be prompted to automatically determine the high time, low time, and average time
in pulsed current mode according to
Figure 7
. These parameters may also be set
manually from the front panel or over the GPIB bus.
Figure 7
Pulsed waveform
The pulsed response of a device is rarely a perfect square wave.
Figure 8
shows
the current response of a typical GSM handset during the transmit portion of the
data frame. Using the built in auto-time feature with a trigger threshold of 0.2 amp
and no trigger delay, the Model 2308 will automatically set the HIGH integration
time, denoted by T
H1
, to 533
μ
s. For this value of HIGH integration time, the effect
of the current transient at the beginning of the pulse is included in the
measurement. Although in this example the effect of the current transient on the
measurement is small, the user can eliminate the effect of the transient by adding
a suitable amount of trigger delay. In this case, a delay of 100
μ
s is sufficient to
eliminate the effect of the transient, approximately 70
μ
s, from the measurement.
Accordingly, the HIGH integration time, T
H2
, must be reduced, in this case 300
μ
s
was chosen, so the integration time does not extend into a section of the pulse the
user does not want to measure.
NOTE
The pulsed waveform in
Figure 7
shows trigger level and the
high, low, and average times set by the Model 2308 using the
auto-time feature.
Trigger
level
Average current
level
High current level
Low current level
High
time
Low
time
Average time
