User`s guide

Agilent E6432A Microwave Synthesizer User’s Guide 3-23

Soft Front Panel Help

Understanding the ALC System

The purpose of the ALC system is to control the amplitude or power

level of the RF energy generated by the synthesizer. It is a feedback

control system, in which the output power is measured and compared to

the desired power level. If the output power level does not equal the

desired power level, the ALC system changes the output until they are

equal.

A desired power level can be set by using either soft front panel controls

or remote VXIplug&play commands. As shown in the ALC System, the

inputs and calibration data are processed by the synthesizer’s assist

processor. The assist processor uses this information to set the Level

DAC. In turn, the Level DAC sends a controlling voltage to the Level

Control Circuits. In the presence of modulation, voltages appearing at

the AM input contribute to the control of the Level Control Circuits.

In synthesizers with an optional step attenuator (Option 1E1), the

power level at the RF output connector can be reduced by the

attenuation of the step attenuator. This is in addition to the control

capabilities provided by the Level Control Circuits.

A feed-back signal to the Level Control Circuits can be provided by

either internal or external detectors. This signal provides the feed-back

voltage that is compared to the voltage representing a desired power

level. This leveling loop allows the synthesizer to provide accurate and

stable power level setting with improved, corrected, source-match at the

internal or external leveling point. Alternately, the power level can be

set without using feed back. In this mode however, power level is

uncalibrated and is subject to drift with temperature.

The following sections describe the operation of the different leveling

modes and leveling points. Two terms are used in the following

discussions: output power and ALC level. Output power is defined as

the actual output power including the affects of the step attenuator

(Option 1E1). In synthesizers without step attenuators, the terms

output power and ALC level are equivalent.