FD7T Series Multi-Output

CMOS Clock Oscillator

May 2008

www.pletronics.com

425-776-1880

4

Description:

The FD7T series Multi-Output CMOS Clock Oscillator is a modular PLL-based low cost, high-performance,

programmable oscillator. The FD7T generates up to seven output frequencies, OUT1 through OUT7.

Frequencies are mutually independent and may be programmed to any frequency from 100KHz to 230-

MHZ and one output can be as low as 12KHz. There are versions including 1 to 4 PLLs, the number of

PLLs impacts the cost.

The FD7T base frequency, as noted in the device part number, is established during manufacture and is

permanently fixed. For convenience, the divider for output OUT1 and the remaining seven output

frequencies, and their characteristics may be pre-programmed at the factory, or field programmed.

The FD7T has a separate output supply pin, V

device supply, V

The FD7xxxTL version has increased output drive for then 1.8V output levels. This version can be used at

1.8V V

The deep M/N PLL divider ratio allows the generation of zero-ppm clocks for applications such as WLAN,

BlueTooth, Ethernet, GPS, USB, IEEE1394, etc. from the base frequency.

Each of the independent PLLs supports Spread Spectrum Clocking (SSC). SSC may be programmed to

be either center-spread or down-spread. This is an important technique to reduce electro-magnetic

interference (EMI).

The device supports non-volatile eePROM programming for easy customization of the device. As

shipped, the device is pre-programmed. Standard combinations are denoted by three characters in the

device part number. However, the FD7T may be reprogrammed to a different configuration.

Reprogramming may be either prior to assembly, or in-circuit via a 2-wire SDA/SCL I

Three programmable control inputs, S0, S1 and S2, may be used to control various aspects of FD7T

operation including selection of alternative frequency set(s), selection of SSC functionality, output tri-state

and power-down.

Reference Oscillator

The Reference Oscillator is an AT cut quartz crystal based oscillator. This oscillator is very similar to the

Pletronics SM77xxH product oscillator. This signal is the lowest jitter and can be an output on Out1,

Out2 or Out3 and can be divided down by the Divider #1. The user may specify any frequency between

12MHz and 32MHz for this reference. All output frequencies are derived from (referenced to) this

Reference Oscillator.

Reference Oscillator - VCXO

The reference oscillator frequency can be modulated by the Vcontrol input, if the VCXO option is

selected. As this Reference Signal is the reference for all other parts of this circuit, all PLLs will be

modulated also.

The VCXO input has a limited voltage range, the VCXO is associated with the internal 1.8V core. A

resistor in series with the Vcontrol input will permit interfacing to 3.3V analog circuits, the voltage range

that changes the frequency will still be limited but the larger voltages swings will not cause problems.