AM Modulation | Agilent Technologies 33120A instruction

Chapter 5 Theory of Operation

AM Modulation

AM Modulation

Blocks 3 and 6 on block diagram page 129; Schematics on pages 136 and 133.

Amplitude modulation is performed by analog multiplier U603 combining the AM_IN and +FUNCTION and -FUNCTION signals. Modulation depths from 0% to 120% are set by varying the signal at AM_IN.

When the amplitude modulation function is selected, the output of U603 is switched into the +AMP_IN signal path by K602. At the same time, the -AMP_IN signal path is grounded, cutting the output signal amplitude in half, to accommodate the more than two times peak signal levels required by >100% modulation depth.

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The AM_IN signal is a combination of any external modulation inputs applied to the rear panel BNC connector and the internally generated AM signals. The function generator can internally synthesize an 8-bit modulation wave shape through DAC U313. Data from any standard or arbitrary wave shape can be used as the modulating wave shape. Modulating wave shapes are automatically expanded or compressed in length, as required, to meet the specified modulating frequency setting. Changes in the function generator output will lag changes in the modulating frequency because new modulation data must be computed and downloaded internally for every frequency change.

The AM_GAIN and AM_OFFSET dc signals are used to calibrate and vary the am modulation depth settings. AM_GAIN controls the peak-to-peak output level from U313 in response to modulation depth setting changes. Likewise, the AM_OFFSET signal varies inversely to the AM_GAIN signal, as the AM depth setting is varied, to produce a constant signal offset in the composite AM_IN modulation signal. The net AM_IN offset is independent of the modulating ac signal component or AM depth setting.

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Agilent Technologies 33120A manual AM Modulation

Contents

Agilent 33120A MHz Function Arbitrary Waveform Generator Service GuidePage Flexible system features Convenient bench-top features Front Panel at a Glance Front-Panel Number Entry MODulation Menu Front-Panel Menu at a Glance Trig Display Annunciators Use the front-panel Input / Output Menu to Rear Panel at a Glance This Book Page Contents Contents Schematics ServiceReplaceable Parts Contents Specifications Waveforms Modulation Characteristics General Specifications Product Dimensions Page Quick Start Quick Start Check the list of supplied items One User’s Guide 〈 This Service GuideConnect the power cord and turn on the function generator To prepare the function generator for use If the function generator does not turn on Verify that there is ac power to the function generatorVerify the power-line voltage setting Verify that the power-line fuse is good Remove the power cord . Remove To adjust the carrying handle Set the units to the desired value To cancel the number mode, press Shift CancelTo set the output frequency Enter the magnitude of the desired frequency Enter the magnitude of the desired amplitude To set the output amplitude Enter the magnitude of the desired offset How to change the offset to -1.5 mVdcEnable the offset modify mode To set a dc offset voltage Output the waveform with the displayed duty cycle To set the duty cycleSelect the square wave function Enter the desired duty cycle Select and output the displayed arbitrary waveform To output a stored arbitrary waveformDisplay the list of arbitrary waveforms Move across to the Exprise choice Enter the magnitude of the desired voltage To output a dc voltage Save the instrument state Set up the function generator to the desired configurationTurn on the state storage mode To store the instrument state Recall the stored instrument state Restore the instrument state To rack mount the function generator Quick Start Front-Panel Menu Operation Front-Panel Menu Operation MODulation Menu Front-panel menu reference Front-panel menu reference SYStem Menu Front-panel menu tutorial Messages Displayed During Menu Use Turn on the menu Move across to the Power on command on this levelMove across to the SYS Menu choice on this level Move down a level to the Parameter choices Cycle the power to restore the default valuesSave the change and turn off the menu Increment the first digit until 300.0 mVPP is displayed Select amplitude adjustment To select the output termination Move down a level to the OUT Term commandMove down a level and then across to the High Z choice Select AM To output a modulated waveformUse the menu to select the shape of the modulating waveform Set the modulating frequency to 200 Hz Move down a level verify that Sine is selectedSet the modulation depth to 80% To unsecure the function generator for calibration Move down a level to the Secured commandMove across to the CAL Menu choice on this level Move down to the parameters level Calibration Procedures Calibration Procedures Calibration Interval Agilent Calibration ServicesTime Required for Calibration Recommended Test Equipment Automating Calibration Procedures Test Considerations Self-Test Performance Verification Tests Quick Performance Check Function Gain and Linearity Verification Frequency Verification AC Amplitude Verification DC Function Offset Verification AC Amplitude Verification Vrms 0.00035 Vrms 15.00 MHz Amplitude Flatness Verification Vrms 0.0061 Vrms AM Modulation Depth Verification Square Wave Duty Cycle Verification Optional Performance Verification Tests Distortion Verification Characters Calibration Security Code To Unsecure the Function Generator Without the Security Code Calibration Message Calibration Count Move across to the Calibrate choice General Calibration/Adjustment ProcedureMove down a level to the Unsecured command Begin the Frequency and Burst Rate adjustment procedure Calculate and save the new value Perform the next adjustment procedure Aborting a Calibration in Progress Frequency and Burst Rate Adjustment AC Amplitude Adjustment High-Z Function Gain and Linearity Adjustment AC Amplitude Adjustment High-Z Frequency Amplitude Modulation Adjustment AC Amplitude Adjustment 50W AC Amplitude Adjustment 50W Adjustment for KHz Setup DC Output Adjustment AC Amplitude Flatness Adjustment Duty Cycle Adjustment AC Amplitude Flatness Adjustment Exiting Output Amplifier Adjustment Optional System Error Messages Error MessagesSelf-Test Error Messages Calibration Error Messages Theory of Operation Theory of Operation Self-test procedures are described in chapter This discussion pertains to the block diagram shown on Block Diagram Overview Output Attenuator Block 8 on block diagram page 129 Schematic on Output Amplifier Block 7 on block diagram page 129 Schematic on 740 R710 R717 740 R710 R711 R715 R716 R719 R720 AM Modulation Square Wave and Sync Block 6 on block diagram page 129 Schematic onBlock 6 on block diagram page 129, schematic on Pre-attenuator Square Wave and Sync Filters Block 5 on block diagram page 129 Schematic on Waveform DAC/Amplitude Leveling/Waveform RAM Block 4 on block diagram page 129 Schematic on Waveform DAC/Amplitude Leveling/Waveform RAM Direct Digital Synthesis DDS Asic Block 2 on block diagram page 129 Schematic on System DACs Block 3 on block diagram page 129 Schematic on Floating Logic Block 1 on block diagram page 129 Schematic on Earth-Referenced Logic Power SuppliesBlock 9 on block diagram page 129 Schematic on Block 10 on block diagram page 129 Schematic on Power Supplies Display and Keyboard Block 11 on block diagram page 129 Schematic onSee Service Service Does the function generator fail self-test? Operating ChecklistIs the function generator inoperative? See To prepare the function generator for use on Call 1-877-447-7278 and ask for Agilent Express Types of Service Available Repackaging for Shipment CleaningAgilent suggests that you always insure shipments Surface Mount Repair Electrostatic Discharge ESD Precautions To Replace the Output Protection Fuse F801 To Replace the Power-Line Fuse Unit Fails Self-Test Troubleshooting HintsUnit Reports Error Unit is Inoperative Power Supply Problems Power-On Self-Test Self-Test Procedures 625 112 Replaceable Parts Replaceable Parts Main PC Assembly 116 117 118 119 120 121 122 123 Display and Keyboard PC Assembly 33120A Mainframe Manufacturer’s List Schematics8 Schematics Block Diagram Pull Off Handle Loosen Captive Sheet 1 132 Sheet 3 Sheet 4 Waveform DAC Schematic 134 Sheet 5 136 Sheet 7 Sheet 8 Output Attenuator Schematic 138 Sheet 9 of 10 Earth Reference Logic Schematic Sheet 10 Power Supplies Schematic 140 Sheet 1 of 1 Display and Keyboard Schematic TOP Side 33120-66521 REV a TOP Side 33120-66502 REV C Manual Part Number