Agilent Technologies 83620A Betriebsanweisung PDF herunterladen (Seite 3)

A major contribution of the 8360 series synthesized

sweepers is their unparalleled leveled output

power accuracy and flatness. This is achieved by

using a digital (vs. analog) design to control the

internal automatic leveling circuitry (ALC).

An internal detector samples the output power

to provide a DC feedback voltage. This voltage is

compared to a reference voltage that is proportional

to the power level chosen by the user. When there

is a discrepancy between voltages, the power is

increased or decreased until the desired output level

is achieved (see figure 3). The factory-generated

internal calibration data of an 8360 is digitally

segmented into 1601 data points across the start/stop

frequency span set by the user. Subsequently, these

points are converted into 1601 reference voltages

for the ALC loop.

The digital ALC control scheme not only delivers

excellent power accuracy and flatness at the output

port of the instrument, but also provides the means

to execute the user flatness correction feature of the

8360. Generally, a power meter is used to create a

table of correction data that will produce flat power

at the test port. The user may measure and enter

correction data for up to 801 points. The correction

data contained in the table is linearly interpolated

to produce a 1601-point data array across the

start/stop frequency span set on the source. This

is summed with the internal calibration data of the

8360 (see figure 4). When user flatness correction

is enabled, the sum of the two arrays will produce

the 1601 reference voltages for the ALC loop.

Theory of operation

Figure 3. Simplified automatic leveling circuitry

Figure 4. ALC calibration correction - summing user flatness correction array

with internal calibration array

Oscillator

modulator

Power

amplifier

Step

attenuator

Leveled

RF output

test

port

Correction

voltage

Leveling

amplifier

Detector

Feedback

voltage

Referece

voltage

1601 equadistant

point array

accessable only

from a computer

User flatness correction array

1 to 801 point frequency-

correction pairs entered

from a computer

or the front panel

1601 points of internal

calibration data

Linear

interpolation

Complete

1601 point

array

Off

CorPair

disable

Fitness

on/off

1601 points

of correction

data

1601 points

of calibration

data

1601

points

for ALC

DAC

∑

1 2 3 4 5 6 7 8 ... 15 16

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