The LMX2594PSEVM uses two LMX2594 synthesizers to generate two phase-coherent outputs with very fine phase adjustment capability. The outputs of the synthesizers can also be combined to produce lower noise and jitter than is possible with just one.
The LMX2594 is a high-performance, wideband synthesizer that can generate any frequency from 10 MHz to 15 GHz without using an internal doubler, thus eliminating the need for sub-harmonic filters.
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The following is included in the package:
The evaluation requires the following hardware and software:
Related evaluation and development resources include:
Apply 3.6 V to Vcc SMA connector. Acceptable supply voltage range is 3.5 V to 5 V. The maximum current consumption in the most extreme configuration must not exceed 1200 mA. The onboard LDOs will provide a 3.3-V supply to the LMX2594 devices.
Connect a low jitter reference clock to the OSCin SMA connector. This clock is evenly distributed to both LMX2594 devices. If a sine wave clock is used, 8 dBm or more input power is suggested.
In category 1 and 2 phase synchronization, the timing of the SYNC signal is not critical. This SYNC signal can be generated from the Reference Pro board. In category 3 phase synchronization, the SYNC signal has to be carefully aligned with the reference clock of the synthesizers. This SYNC signal shall be provided externally to the SYNC SMA connector.
Each LMX2594 device has two RF outputs, but only RFoutA is used. By default, RFoutAP pin is connected to the SMA connector while the RFoutAM pin is terminated onboard. This is the default configuration to measure the phases between the outputs of the LMX2594 devices. With some modification to the EVM, the sum of the two LMX2594 devices output can be obtained from the SumRFout SMA connector. See Section 7 for more information on EVM modification.
Connect the ribbon cable from the Reference PRO to the LMX2594PSEVM.
Connect the USB cable from a PC to the USB port on the Reference PRO board. This provides a power supply to the Reference PRO board and communication with the TICS Pro software. A firmware update may be required. See Section 9.4 for details.
The two LMX2594 devices share the uWIRE socket but only one device can be programmed at a time. Make sure that only one of the DIP switches is in the ON position at a time.
Download and install TICS Pro to a PC. Run the software and follow the following steps to get started.
Use the flow chart in the data sheet to determine the phase synchronization category. If it is a category 3 synchronization, there is limitation to the reference clock frequency and the timing of the SYNC signal with respect to the reference clock is critical. Shown below is a category 3 synchronization example.
If it is a category 3 synchronization, VCO_PHASE_SYNC should be checked to put the devices in SYNC mode. After programming, the outputs from the two LMX2594 devices may not be phase-aligned.
A timing critical SYNC pulse is needed to trigger synchronization.
By combining the output of two synthesizers that are in-phase, a theoretical 3-dB phase noise benefit is possible due to the output power being 6-dB higher while the noise power is only 3-dB higher.
To measure the combined phase noise, some modification to the EVM is needed. See Section 7 for details.
In Figure 3-5, the blue trace shown the phase noise of individual LMX2594 device while the black trace respresented the phase noise of the combined signal.
DESIGNATOR | QUANTITY | DESCRIPTION | PART NUMBER | MANUFACTURER |
---|---|---|---|---|
C1, C2, C3, C4 | 4 | CAP, CERM, 10 µF, 16 V, 10%, X7R, 0805 | EMK212BB7106KG-T | Taiyo Yuden |
C1_LF1, C1_LF2 | 2 | CAP, CERM, 390 pF, 50 V, 5%, C0G/NP0, 0603 | 06035A391JAT2A | AVX |
C2_LF1, C2_LF2 | 2 | CAP, CERM, 0.068 µF, 25 V, 10%, X7R, 0603 | 885012206070 | Wurth Elektronik |
C4_LF1, C4_LF2 | 2 | CAP, CERM, 1800 pF, 50 V, 5%, C0G/NP0, 0603 | GRM1885C1H182JA01D | MuRata |
C5, C8, C9, C10, C12, C22, C23, C24, C26, C27, C33, C35, C36, C37, C40, C41 | 16 | CAP, CERM, 0.1 µF, 16 V, 5%, X7R, 0603 | 0603YC104JAT2A | AVX |
C6, C11, C20, C25, C34, C39 | 6 | CAP, CERM, 1 µF, 16 V, 10%, X7R, 0603 | 885012206052 | Wurth Elektronik |
C7, C16, C17, C18, C21, C31, C32, C38 | 8 | CAP, CERM, 10 µF, 10 V, 10%, X5R, 0603 | GRM188R61A106KAALD | MuRata |
C13, C14, C15, C28, C29, C30, C42, C43 | 8 | CAP, CERM, 0.1 µF, 16 V, 10%, X7R, 0402 | 530L104KT16T | AT Ceramics |
C44, C45 | 2 | CAP, CERM, 4.7 µF, 50 V, X7R, 10%, 0805 | CGA4J1X7R1H475K125AC | TDK Corporation |
D1, D2 | 2 | LED, Green, SMD | LTST-C190GKT | Lite-On |
J1, J2, J4 | 3 | Connector, End launch SMA 50 ohm, TH | 142-0761-881 | Cinch Connectivity |
J3, J5, J6 | 3 | Connector, End launch SMA, 50 ohm, SMT | 142-0701-851 | Cinch Connectivity |
L1, L2 | 2 | Inductor, Multilayer, Air Core, 18 nH, SMD | LQG15HS18NJ02D | MuRata |
R1, R2, R4_LF1, R4_LF2, R26, R30, R35 | 7 | RES, 0, 5%, 0.1 W, 0603 | CRCW06030000Z0EA | Vishay-Dale |
R2_LF1, R2_LF2 | 2 | RES, 68, 5%, 0.1 W, 0603 | CRCW060368R0JNEA | Vishay-Dale |
R3, R3_LF1, R3_LF2, R4, R5, R7, R8, R10 | 8 | RES, 18, 5%, 0.1 W, 0603 | CRCW060318R0JNEA | Vishay-Dale |
R6, R9, R11, R14, R18, R27, R28, R31, R32, R33, R36 | 11 | RES, 12 k, 5%, 0.1 W, 0603 | CRCW060312K0JNEA | Vishay-Dale |
R12, R13 | 2 | RES, 330, 5%, 0.1 W, 0603 | RC0603JR-07330RL | Yageo |
R15, R16, R19, R20 | 4 | RES, 51, 5%, 0.1 W, 0603 | CRCW060351R0JNEA | Vishay-Dale |
R17, R21, R22, R23, R24, R25 | 6 | RES, 50, 0.1%, 0.05 W, 0402 | FC0402E50R0BST1 | Vishay-Dale |
R29, R34 | 2 | RES, 22.1 k, 1%, 0.1 W, 0603 | CRCW060322K1FKEA | Vishay-Dale |
S1, S2 | 2 | Switch, SPST, Slide, Off-On, 4 Pos, SMD | 219-4MST | CTS Electrocomponents |
TP1 | 1 | Test Point, White, TH | 5007 | Keystone Electronics |
U1, U2 | 2 | 15 GHz RF Synthesizer | LMX2594RHAR | Texas Instruments |
U3 | 1 | Power Splitter/Combiner, 50Ohm, 1.8 to 12.5 GHz | EP2C+ | Minicircuits |
U4, U5 | 2 | 1-A, Ultra-Low Noise LDO | TPS7A9401DSCR | Texas Instruments |
uWire | 1 | Header (shrouded), 100 mil, 5x2, Gold, SMT | 52601-S10-8LF | FCI |
C1, C2, C3, C4 | 4 | CAP, CERM, 10 µF, 16 V, 10%, X7R, 0805 | EMK212BB7106KG-T | Taiyo Yuden |
C1_LF1, C1_LF2 | 2 | CAP, CERM, 390 pF, 50 V, 5%, C0G/NP0, 0603 | 06035A391JAT2A | AVX |
The default EVM configuration has the outputs of the LMX2594 devices connected to the RFout1 and RFout2 SMA connectors. To evaluate the phase noise improvement by summing the two outputs together, do the following modifications.
If the EVM does not work as expected, use the following chart to identify potential root causes. Remember:
The Reference PRO board is used to program the LMX2594PSEVM and provide a clean reference clock to LMX2594PSEVM at the same time. The board has several control pins dedicated for control of output format, output frequency, and output enable control. These control pins are configurable through the jumpers by strapping the center pin to Vdd position or GND position. Connections from the Vdd position to the device supply or from the GND position to the ground plane are connected by 1.5-kΩ resistors. By default, the board is configured for 100-MHz LVPECL output. The power supply to Reference PRO is obtained from the PC through a USB connection.
Jumpers FS1 and FS0 are used to set the output frequency.
FS1 | FS0 | OUTPUT FREQUENCY (MHz) |
---|---|---|
GND | GND | 100 |
GND | NC | 312.5 |
GND | Vdd | 125 |
NC | GND | 106.25 |
NC | NC | 156.25 |
NC | Vdd | 212.5 |
Vdd | GND | 62.5 |
The OE pin is used to enable or disable the output.
The OS pin is used to bias internal drivers and change the output format.
OE | OS | OUTPUT FORMAT |
---|---|---|
GND | Don't Care | Disabled |
Vdd | GND | LVPECL |
Vdd | NC | LVDS |
Vdd | Vdd | HCSL |
It is imperative to match the output termination passive components as shown in Table 9-3.
OUTPUT FORMAT | COUPLING | COMPONENT | VALUE |
---|---|---|---|
LVPECL | AC (Default configuration) | R15, R28 | 0 Ω |
R26, R29 | 150 Ω | ||
C24, C25 | 0.01 µF | ||
R27, R30, R31 | DNP | ||
DC(1) | R15, R28, C24, C25 | 0 Ω | |
R26, R27, R29, R30, R31 | DNP | ||
LVDS(2) | AC | R25, R27, R28, R30 | 0 Ω |
R31 | 100 Ω | ||
C24, C25 | 0.01 µF | ||
R26, R29 | DNP | ||
DC | R25, R27, R28, R30, C24, C25 | 0 Ω | |
R31 | 100 Ω | ||
R26, R29 | DNP | ||
HCSL | AC | R15, R28 | 0 Ω |
R26, R29 | 50 Ω | ||
C24, C25 | 0.01 µF | ||
R27, R30, R31 | DNP | ||
DC | R25, R28, C24, C25 | 0 Ω | |
R26, R29 | 50 Ω | ||
R27, R30, R31 | DNP |
Usually when the Reference PRO board is used at the first time, TICS Pro will request for a firmware update. Simply follow the pop-up instructions to complete the update. This is necessary to ensure that the USB connection between the PC and the Reference PRO board is properly set up, otherwise the programming to LMX2594PSEVM will not be successful.
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