DC2248A-B

DEMO MANUAL DC2248A LTC6951 Ultralow Jitter Multi-Output Clock Synthesizer with Integrated VCO Description Demonstration circuit 2248A features the LTC®6951, an Ultralow Jitter Multi-Output Clock Synthesizer with Integrated VCO. For ease of use, the DC2248A is powered from a single 6V supply and comes installed with a 100MHz reference. Direct access to the LTC6951 5V, 3.3V and the reference supplies is possible by removing jumpers. For evaluation of the LTC6951 with other references, the DC2248A can be modified to accommodate different onboard or external components. All differential inputs and outputs have 0.5" spaced SMA connectors. The DC2248A has four AC coupled CML outputs with 50Ω transmission lines making them suitable to drive 50Ω impedance instruments. The LVDS output is DC coupled. The LTC6951’s synchronization functions are made available via the LTC6951 SPI interface, an SMA connector and a turret. The DC2248A can be modified to use an onboard switch and debounce circuit to control the sync pin. A DC2026 (or DC590B) USB serial controller board is used for SPI communication with the LTC6951, controlled by the supplied LTC6951Wizard™ software. Design files for this circuit board are available at http://www.linear.com/demo/DC2248A L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and LT6951Wizard, EZSync ParallelSync and QuikEval are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. OUT4, LVDS DC-COUPLED OUTPUTS, SMA OUT3, CML AC-COUPLED OUTPUTS, SMA RIBBON CABLE CONNECTION TO DC590 OUT0, CML AC-COUPLED OUTPUTS, SMA SUPPLY OPTION, JUMPERS, REFER TO DC2248 RECONFIGURATION OUT1, CML AC-COUPLED OUTPUTS, SMA SINGLE SUPPLY 6V – 9V INPUT, BANANA JACKS, DEFAULT OPTION OUT2, CML AC-COUPLED OUTPUTS, SMA FREQUENCY REFERENCE OPTION, SMA AND TURRET, REFER TO DC2248 RECONFIGURATION SYNC INPUT, SMA AND TURRET, DEFAULT OPTION SYNC OPTION, ONBOARD SWITCH AND DEBOUNCE CIRCUIT REFER TO DC2248 RECONFIGURATION Figure 1. DC2248A Connections dc2248af 1 DEMO MANUAL DC2248A Quick Start Procedure The DC2248A is easy to set up to evaluate the performance of the LTC6951. Follow the procedure below. LTC6951Wizard Installation DC2026 and DC590B Configuration The LTC6951Wizard software is used to communicate with the LTC6951. It uses the DC2026 (or DC590B) to translate between USB and SPI-compatible serial communications formats. It also includes advanced PLL design and simulation capabilities. The following are the LTC6951Wizard system requirements: DC2026: Refer to Figure 2. Set the JP3 jumper to the 3.3V (preferred) or 5V position. • Windows Operating System: Windows XP, Windows 2003 Server, Windows Vista, Windows 7 DC590B: Refer to Figure 2. Set the JP6 jumper to the 3.3V (preferred) or 5V position. JP4 should select “EN”, JP5 “ISO” and “SW” should both select “ON.” • Microsoft .NET 3.5 SP1 or later The LTC6951Wizard and the DC2026 (or DC590B) are required to control the DC2248A through a personal computer (PC). Connect either the DC2026 (or DC590B) to one of your computer’s USB ports with the included USB cable. The DC2026 has the ability to run Linduino code. Refer to http://www.linear.com/solutions/linduino and the Frequently Asked Question section (Question #3) for more details. • Windows Installer 3.1 or later • Linear Technology’s® DC590B or DC2026 (with the DC590B emulator sketch loaded) The DC2026 arrives from the factory with the DC590B emulator sketch loaded. If this is not the case refer to the Troubleshooting section. J1 (DC2026), J4 (DC590B) RIBBON CABLE CONNECTION TO PC J5, USB CONNECTION TO PC J3, USB CONNECTION TO PC JP3 (DC2026), JP6 (DC590B) SELECT 3.3V OPTION JP5 JUMPER JP4 JUMPER Figure 2. DC2026B and DC590B Jumper and Connector Location 2 dc2248af DEMO MANUAL DC2248A Quick Start Procedure Download the LTC6951Wizard setup file at www.linear. com/LTC6951Wizard. 2. Connect the DC2026 (or DC590B) to the DC2248A with the provided ribbon cable. Run the LTC6951Wizard setup file and follow the instructions given on the screen. The setup file will verify and/or install Microsoft .NET and install the LTC6951Wizard. Refer to the LTC6951Wizard Help menu for software operation. 3. Run the LTC6951Wizard application. DC2248A Configuration 4. In LTC6951Wizard, click File → Load Settings and select file “ALL_CHAN_600MHz.6951set”. The DC2248A’s red STATUS LED (D1) should illuminate after step 4. A 600MHz signal should be present on all outputs. 1. Connect J15 and J16 to a power supply and apply power (see Figure 1 and the Typical DC2248A Requirements and Characteristics table). The three green power supply LEDs (D2, D3, D4) should illuminate at this point. Be sure to power down or terminate any unused RF output with 50Ω, or poor spurious performance may result. 5. Synchronize outputs by toggling the LTC6951 SSYNC bit from the LTC6951Wizard. Figure 3. LTC6951Wizard Screenshot dc2248af 3 DEMO MANUAL DC2248A Troubleshooting If the green LEDs (D2, D3, or D4) do not illuminate: 1. Verify J15 measures between 6V and 9V (see the Typical DC2248A Requirements and Characteristics table). 2. Verify JP1, JP2, JP3 jumpers are installed correctly (refer to the DC2248A schematic sheet 3). 3. Verify the voltages at JP1, JP2, and JP3 are correct: a. JP1 = 3.3V b. JP2 = 5V c. JP3 = 3.3V If the red LED (D1) does not illuminate: 1. In LTC6951Wizard’s System tab click “Read All’. LTC6951Wizard should match Figure 3. If not, see “Verify DC2248A and LTC6951Wizard Communication.” 2. In LTC6951Wizard’s System tab, Under Status deselect LOCK and select REFOK. If D1 was does not illuminate then verify “V+XO” test point reads 3.3V. 5. If using the DC2026, Verify the DC2026 has the DC590B Emulator sketch loaded by contacting the factory or following these steps. a. Download QuikEval™ at http://www.linear.com/designtools/software/#Data b. Run QuikEval (Linduino connected to the PC) If QuikEval does not find a DC590B, reload the DC590 Linduino sketch. To use the LTSketchbook refer to the Linduino Quick Start tab at http://www.linear.com/solutions/ linduino for instructions on how to start using Linduino. If DC2248A performance is less than the LTC6951 data sheet specifications or LTC6951Wizard Simulation: 1. For unexpected spurious response, verify power supplies are low noise and spurious free power supplies. Power supplies that are based off a switching regulator architecture are known to generate spurs on PLL/VCO outputs. 1. Ensure the DC2026 (or DC590B) is connected to PC. 2. For poor phase noise results, verify the phase noise specifications of the phase noise measurement instrument. Traditional spectrum analyzers have higher phase noise than the LTC6951 and will degrade measurement results. To measure phase noise performance it is recommended to use a signal source analyzer, such as Keysight’s (previously Agilent/HP) E5052. 2. Disconnect and Reconnect DC2026 (or DC590B) to PC. Contact the factory for further troubleshooting. Verify DC2248A and LTC6951Wizard Communication: To verify communication with the DC2248A, the bottom status line in LTC6951Wizard should read “LTC6951” and “Comm Enabled” as shown in Figure 3. If not, then perform the following steps: 3. Ensure DC2026 (or DC590B) is connected to DC2248A. 4. Close LTC6951Wizard and restart. 4 dc2248af DEMO MANUAL DC2248A dc2248A Reconfiguration The following covers the hardware reconfiguration of the DC2248A. Refer to LTC6951Wizard and the LTC6951 data sheet to better understand how to change programmed parameters on the DC2248A. Power Supply Options Table 1 provides the power supply options for DC2248A. Any combination of onboard LDO or external supplies is possible. By default the DC2248A is set up to use the three onboard LDO’s. Table 1. Power Supply Options VOLTAGE, COMPONENTS JUMPER 3.3V*, U2 100MHz reference JP1 5V, U1 LTC6951 JP2 3.3V, U1 LTC6951, U3, U4, U5 and U9 JP3 ONBOARD LDO EXTERNAL SUPPLY Short Jumper Pins 1–2. Apply 6V–9V to J15/J16. (Default Option). Short Jumper Pins 2–3. Apply appropriate voltage to Jumper Pin 1. Reference Options Table 2 details the available reference options and board modifications for each available option. The 6951set files provided assume the frequency and noise profile of the default reference. If a different reference is used, update the reference frequency and noise profile in LTC6951Wizard before simulating the LTC6951 under the Loop Design tab (see Frequently Asked Questions section, question #3 and the LTC6951Wizard Help menu). Sync Options The LTC6951 data sheet describes several synchronization modes. After selecting the desired synchronization mode, refer to Tables 3 and 4 to select a synchronization programming option and the resulting DC2248A board modifications. Refer to the LTC6951 data sheet for SYNC timing and level requirements. CML Outputs (OUT0, OUT1, OUT2, OUT3) * When using an external reference, power down the onboard reference by shorting JP1 pins 2–3, or poor spurious performance may result. LTC6951 6951SET Files The LTC6951Wizard provides a 6951set file for all LTC6951 data sheet application examples and typical application circuits. After loading a 6951 set file a pop-up window will detail any user actions and board modifications required for the selected file. These same user actions and board modifications are listed in Table 5. The DC2248A has four AC coupled CML outputs. To drive 50Ω impedance instruments connect OUTx+ to the instrument and OUTx– to a 50Ω termination, or vice versa. Refer to LTC6951 data sheet for differential termination options. The V+BIAS turret provides an option to set the DC offset level after the AC coupling capacitor. Modifications are required to use the V+BIAS turret; refer to the DC2248A schematic. LVDS Output (OUT4) Loop Filter Design and Installation Use 6951Wizard to select, design and simulate different loop filters (see Frequently Asked Questions section, question #3). Loop filter components RZ, CI1, CI2, CP, L1 and R1 are located on the top side of the board. Loop filter component C2 is located on the bottom side of the board. The LVDS output is DC coupled without onboard termination by default. The DC2248A provides series and a differential termination resistor options to accommodate other termination networks described in the data sheet. Table 2. Reference Options and Board Modifications DEFAULT REFERENCE OPTION OPTION l INSTALL DEPOPULATE LTC6951 PERFORMANCE COMMENTS Onboard NA NA Limited by onboard reference at frequency offsets