Nanosecond Level UTC Timing Generation and Stamping in CERN's LHC

The General Machine Timing (GMT) at CERN uses an RS-485 multi-drop network through which messages are broadcast by a Central Timing Generator (CTG) module at a rate of 500 kb/s and decoded by many receiver modules in different form factors. For long distance transmission, optical fibers are used. As a result of cabling and capacitive loading of the receivers' inputs, the timing message signal presents an average jitter of 14 ns at any receiver input. For the LHC era, the 500 kb/s rate will be maintained to ensure compatibility with old receivers. However, a special kind of Phase Locked Loop (PLL), involving digital control in a Field Programmable Gate Array (FPGA) and a DAC to control a Voltage Controlled Crystal Oscillator (VCXO), has been developed to generate a 40 MHz square wave at the receiving side which is locked on average to the timing message signal but presents a jitter of less than 1 ns. This 40 MHz signal is locked to UTC because the encoder in the CTG card uses a 40 MHz clock coming from a GPS receiver, and can used to generate pulses or to time-tag external events with high precision. The first timing receiver to use this new PLL is the CTRP card in PMC format. This paper describes the CTRP card with a special emphasis on the PLL part.