3.3/5V Limiting Amplifier for Applications from 100 Mbps to 1.25 Gbps
Figure 4-5. Typical Loss of Signal Hysteresis Characteristic (Full Input Signal Range)
4.0 Electrical Hysteresis = 20*log10(De-assert/Assert)
2.0 1.25 Gbps, 231 - 1
1.0 Vcc = 3.3V, Temp = 25C
5.5 5.7 5.9 6.1 6.3 6.5 6.7 6.9 7.1 7.3 7.5
PECLP and PECLN Termination
The data outputs of the M02046 are PECL compatible. For the high speed PECLP and PECLN outputs any
standard AC or DC-coupling termination technique can be used. Figure 4-6 and Figure 4-7 illustrate typical AC and
AC-coupling is used in applications where the average DC content of the data is zero e.g. SONET. The advantage
of this approach is lower power consumption, no susceptibility to DC drift and compatibility with non-PECL
interfaces. Figure 4-6 shows the circuit configuration and Table 4-2 lists the resistor values. If using transmission
lines other than 50Ω, the shunt terminating resistance ZT should equal twice the impedance of the transmission line
DC-coupling can be used when driving PECL interfaces and has the advantage of a reduced component count. A
Thevenin termination is used at the receive end to give a 50Ω load and the correct DC bias. Figure 4-7 shows the
circuit configuration and Table 4-2 the resistor values.
Alternatively, if available, terminating to VCC - 2V as shown in Figure 4-8 has the advantage that the resistance
value is the same for 3.3V and 5V operation and it also has performance advantages at high data rates.
In the M02046, ST is a PECL output. It is recommended that it be DC terminated in a PECL load, preferably as
shown in Figure 4-8, but the decoupling capacitor on the load is not required as this is a DC output.
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