3.3/5V Limiting Amplifier for Applications from 100 Mbps to 1.25 Gbps
Figure 4-8. Alternative PECL Termination
50 Ω 50 Ω
VCC - 2V
STPECL (M02046-25) Termination
The ST (in the PECL version of the part) output of the M02046 is PECL swing compatible. In most module
applications, it is not common for this output to be terminated into a standard PECL load as shown in Figure 4-8 for
the data outputs because ST is typically in a VOH state and this would consume ~20 mA of continuous supply
current. In cases where an alternative termination can be used it is recommended that a single 510Ω resistor be
connected between the ST output and ground. When this termination is used, the VOH and VOL levels of the ST
output typically meet the standard defined PECL levels and the swing is within PECL limits. This has the additional
advantage of reducing the current consumption due to ST being high to <5 mA.
As shown in the typical applications circuit (Figure 1-2), the LOS output pin can optionally be connected to the Jam
input pin. When LOS asserts the Jam function sets the data outputs to a fixed “one” state (PECLP is held high and
PECLN is held low). This is normally used to allow data to propagate only when the signal is above the users' bit
error rate (BER) requirement. It prevents the outputs from toggling due to noise when no signal is present.
From the LOS assert and deassert figures above (Figure 4-2 - Figure 4-4), when an input signal is below the LOS
assert threshold, LOS asserts (LOS high) causing Jam to assert. When Jam asserts, the data outputs and the
internal servo loop of the M02046-x5 are disabled. If the input signal reaches or exceeds the LOS deassert
threshold, LOS deasserts (LOS low) causing Jam to deassert, and hence enables the data outputs and the internal
servo loop. If, however, the input signal is slowly increasing to a level that does not exceed the LOS deassert
threshold (operating in the hysteresis region), the internal servo loop may not be fully established and this may
cause partial enabling of the data outputs. To avoid this the input signal needs to fully reach or exceed the LOS
deassert level to fully enable the data outputs.
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