Ultralow Noise and Spurious Fractional-N Synthesizer
with Integrated VCO.
There are four options of the DC1959A, one for each ver-
sion of the LTC6948. Table 1 summarizes the available
DC1959A options.
The DC1959A provides 50Ω SMA connectors for the ref-
erence frequency input f
REF
(REF+IN) and the differential
RF output (RF+ and RF–).
Frequency
reference
input,
SMA
Loop
filter
components
A DC590 USB serial controller board is used for SPI com-
munication with the LTC6948, controlled by the supplied
FracNWizard™ software.
Design files for this circuit board are available at
http://www.linear.com/demo/DC1959A
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
FracNWizard is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
Ribbon
cable
connection
to
DC590
5
V
DC
supply,
banana
jacks
3.3
V
DC
supply,
banana
jacks
Mute
jumper
Differential
output,
SMA
Figure 1. DC1959A Connections
dc1959af
1
DEMO MANUAL DC1959A
Quick start proceDure
The DC1959A is easy to set up to evaluate the performance
of the LTC6948. Follow the procedure below.
The DC590 and FracNWizard application are required to
control the DC1959A through a personal computer (PC).
DC590 Configuration
Place the DC590 jumpers in the following positions (refer
to Figure 2):
JP4:
EE – Must be in the EN position.
JP5:
ISO – ON must be selected.
JP5:
SW – ON must be selected.
JP6:
VCCIO – 3.3V must be selected. This sets the SPI
port to 3.3V operation.
n
n
n
Connect the DC590 to one of your computer’s USB ports
with the included USB cable.
FracNWizard Installation
The FracNWizard software is used to communicate with
the LTC6948 synthesizer. It uses the DC590 to translate
between USB and SPI-compatible serial communica-
tions formats. It also includes advanced PLL design and
simulation capabilities. The following are the FracNWizard
system requirements:
n
Windows Operating System: Windows XP, Windows
2003 Server, Windows Vista, Windows 7
Microsoft .NET 3.5 SP1 or later
Windows Installer 3.1 or later
Linear Technology’s DC590 hardware
J4, ribbon
cable
connection
to the
DC1959
J3, USB
connection
to PC
JP6
jumpers
JP4
jumper
JP5 jumpers
Figure 2. DC590 Jumper and Connector Locations
dc1959af
2
DEMO MANUAL DC1959A
Quick start proceDure
Download the FracNWizard setup file at www.linear.com/
FracNWizard.
Run the FracNWizard setup file and follow the instructions
given on the screen. The setup file will verify and/or install
Microsoft .NET and install the FracNWizard. Refer to the
Help menu for software operation.
DC1959A Configuration
1. Connect a 100MHz reference frequency source to REF+IN
(at J1) and signal analyzers to RF+ and/or RF– (at J5
and/or J4) using the SMA connectors (see Figure 1 and
the Typical DC1959A Requirements and Characteristics
table).
Be sure to terminate any unused RF output with 50Ω,
or poor spurious performance may result.
2. Choose the
MUTE
jumper setting:
JP1:
GND/3.3V –
MUTE
position. Select GND to mute
the RF output, 3.3V to un-mute.
3. Connect the GND, 3.3V, and 5V banana jacks to a power
supply and apply power (see Figure 1 and the Typical
DC1959A Requirements and Characteristics table).
4. Connect the DC590 to the DC1959A with the provided
ribbon cable.
5. Run the FracNWizard application.
6. In FracNWizard, click File -> Load Settings and point to
the LTC6948-1_100MHz.fracnset file in case of evaluat-
ing the LTC6948-1, for instance, or load the appropriate
file depending on which option of the LTC6948 you are
evaluating.
The red LED on the DC1959A should turn on indicating
that the loop is locked and the output is at 907MHz.
Figure 3. FracNWizard Screenshot
dc1959af
3
DEMO MANUAL DC1959A
Quick start proceDure
Troubleshooting
If the red LED does not illuminate, follow the instructions
below:
1. Verify that you are able to communicate with the
DC1959A. The bottom status line in FracNWizard should
read LTC6948 and Comm Enabled as shown in Figure 3.
Refer to FracNWizard’s Troubleshoot and Help if not.
2. Verify that the 3.3V and 5V have the correct voltages
on them and that the reference frequency is applied to
the REF+IN SMA input.
If the red LED is on but you cannot detect an RF output,
make sure jumper JP1 is at the 3.3V position. Run Help ->
Troubleshoot in FracNWizard if the problem is not resolved.
DC1959A Reconfiguration
You can redesign the frequency plan of the DC1959A using
FracNWizard. You can change the loop filter as found us-
ing FracNWizard by reinstalling the loop filter components
shown in Figure 1.
assembly options
Table 1. DC1959A Options and Frequency Ranges
ASSEMBLY VERSION
DC1959A-A
DC1959A-B
DC1959A-C
DC1959A-D
PART NUMBER
LTC6948IUFD-1
LTC6948IUFD-2
LTC6948IUFD-3
LTC6948IUFD-4
VCO FREQUENCY RANGE (GHz)
2.240 to 3.740
3.080 to 4.910
3.840 to 5.790
4.200 to 6.390
OUTPUT DIVIDER SETTINGS
Integers 1 through 6
Integers 1 through 6
Integers 1 through 6
Integers 1 through 6
typical Dc1959a reQuirements anD characteristics
PARAMETER
3.3V Power Supply
5V Power Supply
INPUT OR OUTPUT PHYSICAL LOCATION
Input
Input
J6 and J7 Banana Jacks
J8 and J9 Banana Jacks
J1 SMA Connector
J4 and J5 SMA Connectors**
DETAILS
Low-Noise and Spur-Free 3.3V, 130mA
Low-Noise and Spur-Free 5V, 33mA
Low-Noise 100MHz*, 6dBm to 10dBm into 50Ω, See Note
Below
Frequency: 907MHz*, Power: 0dBm, Frequency Range:
Depends on the Version of the LTC6948 Device – Refer to
Table 1
REF+ IN, Reference Frequency Input
RF+ and RF–
Two Outputs
Loop Bandwidth
–
Set by Loop Filter Component Values Approximately 160kHz* Depending on the DC1959A Version
*These frequencies are for the DC1959A fracnset files included with FracNWizard.
**Any
unused RF output must be terminated with 50Ω, or poor spurious performance may result.
Note: A low noise 100MHz reference frequency, such as the Wenzel 501-04516D OCXO, is recommended. If using a different frequency, make sure to
update the Fref and R_DIV boxes under the System tab in FracNWizard so that Fpfd is still 50MHz. For example, if a 250MHz clock is used, Fref should be
changed to 250MHz and R_DIV to 5. Ref BST and FILT under the System tab in FracNWizard might need to be changed if the reference frequency and/or
power is different than what is recommended in the table above. More information can be found in the LTC6948 data sheet.
dc1959af
4
DEMO MANUAL DC1959A
pcb layout
The top metal layer of the DC1959A is shown here as an example of good PCB layout for the LTC6948.
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