M02050_17 Datasheet, PDF (23/28 Pages) M/A-COM Technology Solutions, Inc. – 3.3/5V Limiting Amplifier for Applications to 2.5 Gbps

Applications Information
Figure 4-6. Typical Loss of Signal Hysteresis Characteristic (Full Input Signal Range)
5.0
4.5
4.0 ^{Electrical Hysteresis = 20*log10(De-assert/Assert)}
3.5
3.0
2.5
Conditions:
2.0
2.5 Gbps, 2³¹ - 1
1.5
Vcc = 3.3V, Temp = 25C
1.0
0.5
0.0
5.5 5.7 5.9 6.1 6.3 6.5 6.7 6.9 7.1 7.3 7.5
R_ST (kΩ)
4.1.7
PECLP and PECLN Termination
The outputs of the M02050-15 are PECL compatible and any standard AC or DC-coupling termination technique
can be used. Figure 4-7 and Figure 4-8 illustrate typical AC and DC terminations.
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 inter-
faces. Figure 4-7 shows the circuit configuration and Table 4-2 lists the resistor values. If using transmission lines
other than 50 Ω, the shunt terminating resistance Z_T should equal twice the impedance of the transmission line
(Z_O).
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 50 Ω load and the correct DC bias. Figure 4-8 shows the
circuit configuration and Table 4-2 the resistor values.
Alternatively, if available, terminating to V_CC - 2V as shown in Figure 4-9 has the advantage that the resistance
value is the same for 3.3 V and 5 V operation and it also has performance advantages at high data rates.
Table 4-2.
Supply
5V
3.3V
PECL Termination Resistor Values
Output
Impedance
R_PULL-DOWN
50 Ω
270 Ω
50 Ω
150 Ω
Z_T
100 Ω
100 Ω
R_TA / R_TB
2.7 kΩ / 7.8 kΩ
2.7 kΩ / 4.3 kΩ
R_T / R_B
82 Ω / 130 Ω
130 Ω / 82 Ω
02050-DSH-002-F
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