Pre-attenuator, Square Wave and Sync | Agilent Technologies 33120A

Chapter 5 Theory of Operation

Pre-attenuator

Pre-attenuator

Block 6 on block diagram page 129; Schematic on page 136.

All signals, except square waves, pass through the preattenuator.

The preattenuator multiplexes eight resistive 2 dB attenuators to provide attenuation from 0 dB to 14 dB in 2 dB steps. The 0 dB, 2 dB, and 4 dB attenuation steps are used for level settings between the 6 dB steps selected in the output attenuator section. Amplitude settings between these 2 dB steps are set by smoothly varying the Waveform DAC output level from 0 dB to -2 dB of its nominal level via the AMP_CTL signal. Output attenuator 6 dB steps, preattenuator 0 dB, 2 dB, and 4 dB steps, and small variations (0 dB to 2 dB) of the Waveform DAC output level are combined to produce each amplitude setting.

In the preattenuator, U601 and U602 are operated as 8-to-1 multiplexers, each providing selectable 2 dB attenuation steps. Because of the gain imbalance of the output amplifier (x 12 on +AMP_IN and x (-10) on -AMP_IN), the +signal path U601 has an additional 2 dB attenuation always present (R601 and R602) to equalize the nominal gains in both the plus and minus signal paths.

Square Wave and Sync

Block 6 on block diagram page 129, schematic on page 136.

During square wave outputs, a sine wave signal is generated internally and squared-up by comparator U620. Square wave amplitude control is accomplished by variable gain amplifier Q603 and Q604 and switched into the output signal path through relay K601. A simplified diagram of the square wave generator is shown below.

90

Image 92

Agilent Technologies 33120A manual Pre-attenuator, Square Wave and Sync, Block 6 on block diagram page 129 Schematic on

Contents

Service Guide Agilent 33120A MHz Function Arbitrary Waveform GeneratorPage Convenient bench-top features Flexible system features Front Panel at a Glance Front-Panel Number Entry Front-Panel Menu at a Glance MODulation Menu Display Annunciators Trig Rear Panel at a Glance Use the front-panel Input / Output Menu to This Book Page Contents Contents Replaceable Parts ServiceSchematics Contents Specifications Waveforms Modulation Characteristics General Specifications Product Dimensions Page Quick Start Quick Start One User’s Guide 〈 This Service Guide Connect the power cord and turn on the function generatorTo prepare the function generator for use Check the list of supplied items Verify that there is ac power to the function generator Verify the power-line voltage settingVerify that the power-line fuse is good If the function generator does not turn on Remove the power cord . Remove To adjust the carrying handle To cancel the number mode, press Shift Cancel To set the output frequencyEnter the magnitude of the desired frequency Set the units to the desired value To set the output amplitude Enter the magnitude of the desired amplitude How to change the offset to -1.5 mVdc Enable the offset modify modeTo set a dc offset voltage Enter the magnitude of the desired offset To set the duty cycle Select the square wave functionEnter the desired duty cycle Output the waveform with the displayed duty cycle To output a stored arbitrary waveform Display the list of arbitrary waveformsMove across to the Exprise choice Select and output the displayed arbitrary waveform To output a dc voltage Enter the magnitude of the desired voltage Set up the function generator to the desired configuration Turn on the state storage modeTo store the instrument state Save the instrument state Restore the instrument state Recall the stored instrument state To rack mount the function generator Quick Start Front-Panel Menu Operation Front-Panel Menu Operation Front-panel menu reference MODulation Menu Front-panel menu reference SYStem Menu Front-panel menu tutorial Messages Displayed During Menu Use Move across to the SYS Menu choice on this level Move across to the Power on command on this levelTurn on the menu Save the change and turn off the menu Cycle the power to restore the default valuesMove down a level to the Parameter choices Select amplitude adjustment Increment the first digit until 300.0 mVPP is displayed Move down a level and then across to the High Z choice Move down a level to the OUT Term commandTo select the output termination Use the menu to select the shape of the modulating waveform To output a modulated waveformSelect AM Set the modulation depth to 80% Move down a level verify that Sine is selectedSet the modulating frequency to 200 Hz Move across to the CAL Menu choice on this level Move down a level to the Secured commandTo unsecure the function generator for calibration Move down to the parameters level Calibration Procedures Calibration Procedures Time Required for Calibration Agilent Calibration ServicesCalibration Interval Automating Calibration Procedures Recommended Test Equipment Test Considerations Performance Verification Tests Self-Test Quick Performance Check Frequency Verification Function Gain and Linearity Verification DC Function Offset Verification AC Amplitude Verification AC Amplitude Verification Vrms 0.00035 Vrms Amplitude Flatness Verification 15.00 MHz AM Modulation Depth Verification Vrms 0.0061 Vrms Optional Performance Verification Tests Square Wave Duty Cycle Verification Distortion Verification Calibration Security Code Characters To Unsecure the Function Generator Without the Security Code Calibration Count Calibration Message General Calibration/Adjustment Procedure Move down a level to the Unsecured commandBegin the Frequency and Burst Rate adjustment procedure Move across to the Calibrate choice Perform the next adjustment procedure Calculate and save the new value Frequency and Burst Rate Adjustment Aborting a Calibration in Progress Function Gain and Linearity Adjustment AC Amplitude Adjustment High-Z AC Amplitude Adjustment High-Z Modulation Adjustment Frequency Amplitude AC Amplitude Adjustment 50W AC Amplitude Adjustment 50W Adjustment for KHz DC Output Adjustment Setup Duty Cycle Adjustment AC Amplitude Flatness Adjustment AC Amplitude Flatness Adjustment Exiting Output Amplifier Adjustment Optional Self-Test Error Messages Error MessagesSystem Error Messages Calibration Error Messages Theory of Operation Self-test procedures are described in chapter Theory of Operation Block Diagram Overview This discussion pertains to the block diagram shown on Block 8 on block diagram page 129 Schematic on Output Attenuator Block 7 on block diagram page 129 Schematic on Output Amplifier 740 R710 R717 740 R710 R711 R715 R716 R719 R720 AM Modulation Block 6 on block diagram page 129 Schematic on Block 6 on block diagram page 129, schematic onPre-attenuator Square Wave and Sync Square Wave and Sync Block 5 on block diagram page 129 Schematic on Filters Block 4 on block diagram page 129 Schematic on Waveform DAC/Amplitude Leveling/Waveform RAM Waveform DAC/Amplitude Leveling/Waveform RAM Block 2 on block diagram page 129 Schematic on Direct Digital Synthesis DDS Asic Block 3 on block diagram page 129 Schematic on System DACs Block 1 on block diagram page 129 Schematic on Floating Logic Power Supplies Block 9 on block diagram page 129 Schematic onBlock 10 on block diagram page 129 Schematic on Earth-Referenced Logic Power Supplies See Block 11 on block diagram page 129 Schematic onDisplay and Keyboard Service Service Operating Checklist Is the function generator inoperative?See To prepare the function generator for use on Does the function generator fail self-test? Types of Service Available Call 1-877-447-7278 and ask for Agilent Express Agilent suggests that you always insure shipments CleaningRepackaging for Shipment Electrostatic Discharge ESD Precautions Surface Mount Repair To Replace the Power-Line Fuse To Replace the Output Protection Fuse F801 Troubleshooting Hints Unit Reports ErrorUnit is Inoperative Unit Fails Self-Test Power Supply Problems Self-Test Procedures Power-On Self-Test 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