Take a closer look – Atec Agilent-U2000 Series User Manual
Page 6
6
Take a Closer Look
Diode-based sensors frequently
rely on the application of correction
factors to extend their dynamic range
beyond their square-law region, typi-
cally in the range of –70 to –20 dBm.
While this technique achieves
measurement of CW signals over
a wide dynamic range, it fails to do
so for modulated signals when the
signal level is above the square-law
region. Modulated signals must be
padded down, with their average and
peak power levels within the diode
square-law region, for accurate aver-
age power measurement.
The U2000 Series USB power sensors
are true-average, wide-dynamic-range
RF/microwave power sensors,
based on a dual-sensor diode pair/
attenuator/diode pair topology as
proposed by Szente et. al. in 1990
1
.
The simplified block diagram shown
here illustrates this technique.
This technique ensures diodes in the
selected signal path are kept in their
square law region—with output cur-
rent and voltage proportional to input
power. The diode pair/attenuator/
1. US Patent #4943764, assigned to Hewlett-Packard Company
2. November 1986 Hewlett-Packard Journal pages 14-2, “Diode Integrated Circuits for Millimeter-Wave Applications”
3. Refer to “Maximum Power” on page 9 for maximum power handling specifications
RF in
Low Sense+
Low Sense–
High Sense+
High Sense–
diode pair assembly can then yield
the average of complex modulation
formats across a wide dynamic range,
irrespective of signal bandwidth.
The dual-range Modified Barrier
Integrated Diode (MBID)
2
package
incorporates diode stacks in place of
single diodes. This further improves
measurement accuracy of high-level
signals with high crest factors with-
out incurring damage
3
to the sensor.
Implementation of both techniques in
the U2000 Series USB sensors enable
effective average power measure-
ments of a wide range of signals,
including multitone and spread spec-
trum signals used in CDMA, W-CDMA
and digital television sytems.
Built-in triggering port for
synchronization with external
instruments or events
LED indicator for PC communication
Small and lightweight build
Secure locking mechanism
USB 2.0-compliant cable
for connection to PC or
other instruments