Principles Of Operation - Agilent Technologies U2000H Operating And Service Manual

1 Introduction

Principles of Operation

The U2000 Series USB power sensors function as power meter and power
sensor in one device. The U2000 Series has the capability of sensing the signal,
acquiring the data and signal conditioning, processing the data and fulfilling
communication function as in other Agilent test instruments.
The low power measurement path is a 2- diode stacks and the high power path
contains 5- diode stacks which extend the dynamic range square- law
detection. The range selection is performed automatically by the product
based on the measured power levels. The sensing element technology has been
previously used in the popular E9300 Series sensors. The new U2000 Series
includes all the signal conditioning and analog- to- digital formatting
functions that have been in use for several years. Thus, you can be assured
that the U2000 Series USB power sensors will deliver highly predictable
results.
The main component for the sensing element of the U2000 Series is the RF
input port assembly which provides a 50 Ω load to the RF signal applied to the
power sensor. A dual range GaAs diode pair/attenuator/diode pair assembly
in the RF input port rectifies the applied RF to produce dc voltages (high and
low ranges) which vary with the RF power across the 50 Ω load. Thus the
voltage varies with the RF power dissipated in the load.
The low- level dc voltage from the Rf input port assembly is picked up by the
signal conditioning part of the product which consists of high isolation
switches, chopper circuitry and high gain amplifier. Differential electronics is
maintained from the sensing element up to the 14- bit Analog- to- Digital
converter (ADC) for signal integrity and noise immunity. Amplification and
signal conditioning assure that drift and gain stability are not compromised
before hitting the high performance 14- bit analog- to- digital converter
modules. From there, the digitized power data enters the processor which
operates as an on- board computer for the self- contained sensor.
Products control and processing is provided by an Embedded Processor with
Digital Signal Processing (DSP) capability which is supported by a 64 MB
SDRAM. The available processing power enables the implementation of
* Agilent Fundamentals of RF and Microwave Power Measurements (Part 2), Power Sensors and
6
*
Instrumentation, Literature Number 5988-9214EN
Anderson, Alan B., October, 2000, Measuring Power Levels in Modern Communication Systems,
MW/RF Magazine
U2000 Series Operating and Service Guide