1022410 – 0001 Rev. 2
UMOD hardware theory of operation 3–27
•
External clock—The transmit timing generator is phase
locked to a user supplied clock (either a terrestrial data
clock or a station clock).
Receive timing generator
Figure 3-13 is a block diagram of the receive timing generator.
The RXTG provides the following clocks signals:
•
Receive overhead channel rate clock (information
rate x 256/255)
•
Receive Viterbi encoding symbol rate
•
Receive Reed-Solomon encoding symbol rate
•
Receive information
•
Framing overhead clock
•
Demodulator clock
RXTG operation is identical to the TXTG. The clock signals are
generated by a programmable sequencer that punctures a
high-speed clock sourced by an NCO. The NCO output clock
frequency is programmable through its CP interface. The RXTG
receives its reference clock from a highly-stable reference
oscillator and is phase-locked to the recovered symbol clock from
the demodulator. A digital PLL, wherein the CP calculates and
inputs correction values to the NCO, is used to maintain lock with
the recovered clock.
