Preliminary Data Sheet
October 2000
T7630 Dual T1/E1 5.0 V Short-Haul Terminator (Terminator II)
110
L Lucent Technologies Inc.
Phase-Lock Loop Circuit
The T7630 allows for independent transmit path and
receive path clocking. The device provides outputs to
control variable clock oscillators on both the transmit
and receive paths. As such, the system may have both
the transmit and receive paths phase-locked to two
autonomous clock sources.
The block diagram of the T7630 phase detector cir-
cuitry is shown in Figure 49. The T7630 uses elastic
store buffers (two frames) to accommodate the transfer
of data from the system interface clock rate of
2.048 Mbits/s to the line interface clock rate of either
1.544 Mbits/s or 2.048 Mbits/s. The transmit line side of
the T7630 does not have any mechanism to monitor
data overruns or underruns (slips) in its elastic store
buffer. This interface relies on the requirement that the
PLLCK clock signal (variable) is phase-locked to the
RCHICK clock signal (reference). When this require-
ment is not met, uncontrolled slips may occur in the
transmit elastic store buffer that would result in corrupt-
ing data and no indication will be given. Typically, a
variable clock oscillator (VCXO) is used to drive the
PLLCK signal. The T7630 provides a phase error sig-
nal (PLLCK-EPLL) that can be used to control the
VCXO. The PLLCK-EPLL signal is generated by moni-
toring the divided-down PLLCK (DIV-PLLCK) and
RCHICK (DIV-RCHICK) signals. The DIV-RCHICK sig-
nal is used as the reference to determine the phase dif-
ference between DIV-RCHICK and DIV-PLLCK. While
DIV-RCHICK and DIVPLLCK are phase-locked, the
PLLCK-EPLL signal is in a high-impedance state. A
phase difference between DIV-RCHICK and DIV-
PLLCK drives PLLCK-EPLL to either 5 V or 0 V. An
appropriate loop filter, for example, an RC circuit with
R = 1 k
and C = 0.1
μ
F) is used to filter these PLLCK-
EPLL pulses to control the VCXO.
The system can force TCHICK to be phase-locked to
RLCK by using RLCK as a reference signal to control a
VCXO that is sourcing the TCHICK signal. The T7630
uses the receive line signal (RLCK) as the reference
and the TCHICK signal as the variable signal. The
T7630 provides a phase error signal (TCHICK-EPLL)
that can be used to control the VCXO generating TCH-
ICK. The TCHICK-EPLL signal is generated by moni-
toring the divided-down TCHICK signal (DIV-TCHICK)
and RLCK (DIV-RLCK) signals. The DIV-RLCK signal
is used as the reference to determine the phase differ-
ence between DIV-TCHICK and DIV-RLCK. While DIV-
RLCK and DIV-TCHICK are phase-locked, the TCH-
ICK-EPLL signal is in a high-impedance state. A phase
difference between DIV-RLCK and DIV-TCHICK drives
TCHICK-EPLL to either 5 V or 0 V. An appropriate loop
filter, for example, an RC circuit with R = 1 k
and
C = 0.1
μ
F, is used to filter these TCHICK-EPLL pulses
to control the VCXO. In this mode, the T7630 can be
programmed to act as a master timing source and is
capable of generating the system frame synchroniza-
tion signal through the TCHIFS pin by setting
FRM_PR45 bit 4 to 1.