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Take a closer look – Atec Agilent-U2000 Series User Manual

Page 6

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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