AND8020 Datasheet, PDF (14/18 Pages) Analog Devices – Termination of ECL Logic Devices with EF (Emitter Follower) OUTPUT Structure

SECTION 5. DIODE TERMINATION
V_BB
Driver
D1
*
*
D2
Receiver
*All Media ^D1
D2
V_BB
AND8020/D
Alternative to the resistor network termination schemes,
a Diode method shown in Figure 19 may afford certain
advantages when a design has the following constraints.
1. Impedance controlled media line is not required
(coax, twisted pair, striplines, etc.)
2. Impedance matched termination network is not
required.
3. Overshoot and Noise need to be clamped to logic
HIGH/LOW levels.
V_BB
Driver
*All Media
Driver
D1
*
*
D2
Receiver
D1
D2
V_BB
*
Receiver
*All Media
D1
D2
V_BB
Figure 19. Diode Termination
D1 and D2 diodes may be an MBD301, MMBD301,
MBD701, MMBD701LT1, or a dual package MMBD452LT1.
Diode forward voltage curves from a data sheet, such as shown
in Figure 20, will determine specific current and voltage
operation range. Frequency limitations may be a consideration
when selecting the diodes. The Silicon Hot−Carrier Schottky
Barrier diode MBD701, for example, displays a forward V_f of
about 0.55 V and an I_f of about 11 mA (at 25°C) to match a
50 W impedance line. At higher temperatures, the current
decreases.
100
T_A = 85°C
10
1.0
T_A =−40°C
T_A = 25°C
0.1
0 0.2 0.4
0.8
1.2
1.6
2.0
V_F, FORWARD VOLTAGE (V)
Figure 20. MMBD701 Diode Forward Voltage
http://onsemi.com
14