oq2541bhp NXP Semiconductors, oq2541bhp Datasheet - Page 10

• Manufacturer Part Number: oq2541bhp
• Description: Oq2541bhp; Oq2541bu Sdh/sonet Data And Clock Recovery Unit Stm1/4/16 Oc3/12/48 Ge
• Manufacturer: NXP Semiconductors

Philips Semiconductors
The LOS function will only work properly if the input signal
is larger than the input offset of the OQ2541B. Otherwise,
the signal will be masked by the input offset and
interpreted as consecutive bits of the same sign, thus
obstructing a proper LOS detection. In practice, an optical
front-end device with a noise level (RMS value) larger than
the specified offset of the OQ2541B will ensure a proper
LOS indication.
The LOS detection is BER related, but neither dependent
on the data stream content nor protocol. Therefore, an
SDH/SONET data stream is not a prerequisite for a proper
LOS function. Since the LOS function of the OQ2541B is
derived from digital signals, it is a good supplement to an
analog, amplitude based, LOS indication.
Pin LOS is an open-collector TTL compatible output.
A pull-up resistor is to be connected to a positive supply
voltage.
The LOS pin will be at a HIGH level (TTL) if the data signal
is absent on pins DIN and DINQ or if BER > 5
Otherwise, pin LOS will be at a LOW level if
BER < 1
Reference frequency select
A reference clock signal of 19.44 or 38.88 MHz must be
connected to pins CREF and CREFQ. It should be noted
that the reference frequency should be either
39.0625 or 19.53125 MHz in a GE system. Pin DREF19 is
used to select the appropriate output frequency at
frequency divider 2 (see Table 2).
To minimize the adverse influence of reference clock
crosstalk, a differential signal with an amplitude from
75 to 150 mV (p-p) is advised.
Since the reference clock is only used as an acquisition aid
for the PLL of the frequency window detector, the quality
of the reference clock (i.e. phase noise) is not important.
There is no phase noise specification imposed on the
reference clock generator and even frequency stability
may be in the order of 100 ppm. In general, most
inexpensive crystal-based oscillators are suitable.
When the OQ2541B is used in an application with a fixed
reference clock frequency, it is best to connect
pin DREF19 through a short track or a via to the ground
plane or pin V
is required in the application, the pin can be controlled
through a low ohmic switching FET, e.g. BSH103 or
equivalent (low R
2000 Sep 18
SDH/SONET data and clock recovery unit
STM1/4/16 OC3/12/48 GE
10
EE
3
.
. If a selectable reference clock frequency
DSon
).
10
2
.
10
Table 2 Reference frequency selection
STM mode selection
The VCRO has a large tuning range. However, the
performance of the OQ2541B is optimized for
SDH/SONET, including GE bit rates.
Due to the nature of the PLL, the wide tuning range is a
necessity for proper lock behaviour over the guaranteed
temperature range, aging and batch to batch spread.
Though it might seem that the OQ2541B is capable of
recovering other bit rates than SDH/SONET and
GE bit rates (STM1/OC3, STM4/OC12, STM16/OC48 and
1250 Mbits/s), the behaviour cannot be guaranteed.
The required SDH/SONET bit rate is selected by
connecting pins DOUT155, DOUT622 and DOUT1250
to ground or to the supply voltage V
The connections to V
few mA and should have low resistance and inductance.
Therefore, short printed-circuit board tracks are
recommended. In some cases, a small decoupling
capacitor (approximately 100 pF) near the selection pins
might be necessary to provide a clean return path for
RF currents.
When the OQ2541B is used in an application with a fixed
data rate, it is best to connect pins DOUT155, DOUT622
and DOUT1250 through a short track or a via to the ground
plane or pin V
application, the pins can be controlled through low-ohmic
switching FETs, e.g. BSH103 or equivalent (low R
For STM16/OC48 (2488.32 Mbits/s) operation, all three
pins have to be connected to ground
For GE (1250 Mbits/s) operation, pin DOUT1250 has to
be connected to V
For STM4/OC12 (622.08 Mbits/s) operation,
pins DOUT1250 and DOUT622 have to be connected
to V
For STM1/OC3 (155,52 Mbits/s) operation, all three pins
have to be connected to V
FREQUENCY
EE
(MHz)
38.88
19.44
(the dividers are daisy chained)
EE
OQ2541BHP; OQ2541BU
. If a selectable bit rate is required in the
EE
EE
DIVISION
and ground carry a current of a
FACTOR
128
64
EE
.
EE
Product specification
(see Table 3):
LEVEL ON PIN
DREF19
ground
V
EE
DSon
).