Datasheet

3 Block Description
3.1 Block A
3.2 Block B
3.3 Block C
3.4 Block D
4 Software-Selectable Options
Block Description www.ti.com
This section summarizes the function of each block.
Block A includes a CDCE421A QFN device that accepts an LVCMOS reference input through the vertical
SMA input connector (Ref Input), which is already ac-coupled onboard the EVM.
This block includes a CDCE421A QFN device that uses an AT crystal. This block can be used as either a
crystal oscillator (XO) or a voltage-controlled crystal oscillator (VCXO). For use as an XO or VCXO, the
crystal should be mounted on either of the two crystal footprints on the board, and a vertical SMA input
connector must be installed on the provided footprint to be used as the control voltage input.
Block C can accommodate a 5 × 7 crystal oscillator. The oscillator package must also include a
fixed-frequency crystal with a specified load and range.
Block D includes a socket that fits the oscillator part used in block C.
The output frequency of the CDCE421A is always an integer multiple or integer divide of the input
frequency. The output frequency is determined through the selection of VCO1 or VCO2 and the
appropriate prescalar and output divider based on the values discussed in the CDCE421A product data
sheet .
The loop filter selection will affect the output frequency phase noise, and should be considered in
conjunction with the type of input used.
In LVDS mode, the device can achieve up to 400 MHz. In LVPECL mode, the device can achieve up to
1.175 GHz. The output signaling level and LVPECL termination are selectable through the software
interface.
The provided graphical user interface (GUI) software allows users to easily send commands to the
CDCE421A through the host-powered USB interface. The EVM includes a slave USB controller that
transmits the commands to the single-pin programming interface located on the CDCE421A. DC power for
the USB controller can either be derived from the 5-V power pin in the USB cable or by using an external
5-V ac adapter in the slot available on the EVM.
In addition to writing commands to the CDCE421A SRAM while the board is powered up, commands can
also be stored in either the nonvolatile USB microcontroller memory or the EEPROM included within the
CDCE421A. This option allows users to start the EVM in the desired state without requiring additional
programming at power-up.
Note: The CDCE421A does have a permanent EEPROM lock mode. After this mode, is selected
the EEPROM within the CDCE421A cannot be changed. This option is useful when setting
final configurations.
10.9-MHz to 1.175-GHz, Low Phase Noise Clock Evaluation Board4 SCAU031 – June 2009
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