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SMD-00191 Rev D

Subject to Change Without Notice

PFD1K

Charge Pump Control:

The PFD1K charge pump outputs are differential CML outputs with 100 ohm terminations. With this

design the charge pump pulse width can be as small as 100 ps. The charge pump output pulses

are digitally programmable with a 4 bit parallel interface. The maximum current output of the charge

pump is 12 mA which will produce a pulse of 1200 mVpp into the internal 100 ohm termination resis-

tor. When the charge pump outputs are terminated with a 50ohm load the parallel impedance of 100

ohms and 50 ohms results in a 33 ohm load, which reduces the output to 400mVpp. In addition to

the digital control, there is an analog charge pump control voltage, VADJ, which can be used for fine

control of the charge pump current. The maximum charge pump output of 12mA occurs when VADJ

is set to VCC (which is the normal mode of operation). Logic 1 on the POL control input reverses the

polarity of the charge pump outputs.

Simplified Charge Pump Output Circuit