Direct Digital Synthesis DDS Asic | Agilent Technologies 33120A

Chapter 5 Theory of Operation

Direct Digital Synthesis (DDS ASIC)

Direct Digital Synthesis (DDS ASIC)

Block 2 on block diagram page 129; Schematic on page 132.

The DDS ASIC, U206, controls the WA (waveform address) and MA (modulation address) busses. The waveform address is used by the waveform RAMs U404 and U405. The modulation data bus is used by the modulation RAM U205.

The DDS ASIC is comprised of several internal registers and addressing state machines. Instructions are written to the DDS ASIC by the main CPU via memory mapped control registers U108 and U202. When loading data into Waveform RAM or Modulation RAM, addresses on the WA and MA busses are incremented by ASIC U206. ASIC addresses are incremented by each rising edge of the TRIG line while writing data into these RAM. The state of the HOST_RQ* line controls whether the main CPU or the modulation RAM U205 is sourcing instructions to the DDS ASIC internal state machines. The Modulation RAM is loaded with frequency values and amplitude flatness correction values or AM modulation data for latch U309 and AM dac U313. Data multiplexer U217 and flip-flop U215 are used to preselect and synchronize the modulation sync source available to the SYNC output terminal multiplexer U604.

The external trigger input OGEXT is optically isolated by U213 and

applied to an input of trigger source multiplexer U214. The external 5 trigger input is used for triggering the start of a frequency sweep or

burst output and for externally gating the output signal on and off asynchronously. U214 selects one of seven trigger sources for use by U206 for initiating its internal program.

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Agilent Technologies 33120A manual Direct Digital Synthesis DDS Asic, Block 2 on block diagram page 129 Schematic on

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 Connect the power cord and turn on the function generator One User’s Guide 〈 This Service GuideTo prepare the function generator for use Check the list of supplied items Verify the power-line voltage setting Verify that there is ac power to the function generatorVerify 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 set the output frequency To cancel the number mode, press Shift CancelEnter the magnitude of the desired frequency Set the units to the desired value Enter the magnitude of the desired amplitude To set the output amplitude Enable the offset modify mode How to change the offset to -1.5 mVdcTo set a dc offset voltage Enter the magnitude of the desired offset Select the square wave function To set the duty cycleEnter the desired duty cycle Output the waveform with the displayed duty cycle Display the list of arbitrary waveforms To output a stored arbitrary waveformMove across to the Exprise choice Select and output the displayed arbitrary waveform Enter the magnitude of the desired voltage To output a dc voltage Turn on the state storage mode Set up the function generator to the desired configurationTo store the instrument state Save 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 down a level to the Unsecured command General Calibration/Adjustment ProcedureBegin the Frequency and Burst Rate adjustment procedure Move across to the Calibrate choice 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 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 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 Block 9 on block diagram page 129 Schematic on Power SuppliesBlock 10 on block diagram page 129 Schematic on Earth-Referenced Logic Power Supplies Display and Keyboard Block 11 on block diagram page 129 Schematic onSee Service Service Is the function generator inoperative? Operating ChecklistSee To prepare the function generator for use on Does the function generator fail self-test? 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 Reports Error Troubleshooting HintsUnit is Inoperative Unit Fails Self-Test 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