AN1002
Interfacing Between ECL / LVECL / PECL /
LVPECL - to - TTL / LVTTL / CMOS / LVCMOS
HIGH-PERFORMANCE PRODUCTS
When going from ECL / LVECL / PECL / LVPECL environ-
ment to TTL / CMOS or LVTTL / LVCMOS and vise versa,
signal integrity and duty cycle distortion can play an im-
portant role in the success of a design. To avoid running
into such issues, use of integrated circuit translator chips
is highly recommended because the I/O switching lev-
els, propagation delay, and other parameters can be con-
trolled over the full supply voltage and ambient tem-
perature range. Controlling such parameters using dis-
crete logic is extremely difficult since the voltage levels
would shift with respect to supply voltage and tempera-
ture fluctuation. Semtech’s high performance products
are available to perform such signal translation from ECL
/ PECL to TTL / CMOS and vice versa while meeting the
crucial design requirements mentioned earlier. These
devices operate over an extended supply voltage range
covering both 5.0V and 3.3V modes of operation. For
ECL / PECL output termination refer to application note
AN1003.
TTL / LVTTL / CMOS / LVCMOS to PECL / LVPECL Translators
Device
SK10/100ELT20W
SK10/100ELT22W
Function
LVTTL / LVCMOS to LVPECL and TTL / CMOS to PECL Translator
Dual LVTTL / LVCMOS to LVPECL and TTL / CMOS to PECL
Translator
Package Type
8 PIN
SOIC/MSOP
8 PIN
SOIC/MSOP
Operating Voltage
3.0V to 5.5V
3.0V to 5.5V
PECL / LVPECL to TTL / LVTTL / CMOS / LVCMOS Translators
D ev i c e
SK10/100ELT21W
SK100ELT23W
Function
Differential PECL to CMOS / TTL and LVPECL to LVCMOS
/ LVTTL Translator
Dual Differential PECL to CMOS / TTL and LVPECL to
LVCMOS / LVTTL Translator
Package Type
8 PIN SOIC
Operating Voltage
3.0V to 5.5V
8 PIN SOIC
3.0V to 5.5V
TTL / LVTTL / CMOS / LVCMOS to ECL / LVECL Translator
Device
SK10/100ELT24W
Function
TTL / CMOS to ECL and LVTTL / LVCMOS to LVECL
Translator
Package Type
8 PIN
SOIC/MSOP
Operating Voltage
+3.0V to +5.5V /
-5.5V to -3.0V
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AN1002
HIGH-PERFORMANCE PRODUCTS
ECL / LVECL to TTL / LVTTL / CMOS / LVCMOS Translator
Device
SK10/100ELT25W
Function
Differential ECL to TTL / CMOS and LVECL to LVTTL /
LVCMOS Translator
Package Type
8 PIN SOIC
Operating Voltage
-5.5V to -3.0V /
+.30V to +5.5V
Translating ECL / LVECL to PECL / LVPECL or vice
versa, proves to be a more challenging task com-
pared to TTL / CMOS type signals. With ECL type
signals being greater than 200 MHz and usually
reaching into Giga Hertz range in speed, we have to
use extreme care in board layout, noise filtering,
signal integrity, proper output termination, and jitter,
to name a few, when switching between positive
and negative regions. Talking about the issues
mentioned above is beyond the scope of this
application note and we will concentrate only on
providing a solution for ECL to PECL signal level
translation and vice versa. Capacitive coupling
method is one of the alternative solutions used by
designers when interfacing ECL with PECL signals.
As we mentioned before, using discrete logic can
hinder the system performance; therefore, to avoid
such problems use of translator devices is highly
recommended. Semtech offer both ECL / LVECL to
PECL / LVPECL and PECL / LVPECL to ECL / LVECL
translators.
ECL / LVECL / PECL / LVPECL Translators
Device
SK10/100EL90W
SK10/100EL91W
Function
Triple ECL to PECL/LVPECL and LVECL to PECL/LVPECL
Translator
Triple PECL to ECL/LVECL and LVPECL to ECL/LVECL
Translator
Package Type
20 PIN SOIC
20 PIN SOIC
Operating Voltage
-5.5 to -3.0V /
+3.0 to +5.5V
-5.5 to -3.0V /
+3.0 to +5.5V
Using the two translators, SK10/100EL90W and
SK10/100EL91W, we will show some examples of
how these devices are used. Figures 1, 2, 3, and 4
show SK100EL90W and SK100EL91W in different
ECL / LVECL / PECL / LVPECL translation schemes.
What is important in these figures is that the inputs
are used in three different ways and accordingly their
corresponding outputs are properly terminated.
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The three modes are: inputs driven differentially,
single-ended, or left open. Please note that only
the Thevenin equivalent parallel termination scheme
is shown here, for alternate termination schemes
refer to application note AN1003. Furthermore,
power supply noise filtering scheme is not shown in
these examples.
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AN1002
HIGH-PERFORMANCE PRODUCTS
APPLICATION NOTES
(contintued)
SK100EL90W in LVECL - to - PECL or LVPECL Mode Configuration
VCC = 0V
VCC = +3.3V
or 5.0V
GND = 0V
R1
R1
SK100EL90W
R1
VCC
1
20
V
CC
19
LVPECL
LVECL
2
DO
Q0
3
DO*
R2
R2
18
Q0*
VCC =+3.3V or 5.0V
R2
R1
R1
R1
R1
VEE = -3.3V
Single Ended
Mode
VBB
4
5
17
GND
16
LVPECL
LVECL
LVECL DEVICE
D1
R2
GND = 0V
R1
Q1
PECL / LVPECL
DEVICE
6
D1*
15
R2
R2
Q1*
R2
R2
GND
VEE = -3.3V
VBB
7
8
14
13
LVPECL
LVECL
GND
GND
Q2
D2
0.1µF
Unused
Input
9
10
12
Q2*
D2*
VEE
-3.3V
GND
11
VCC
VEE = - 3.3V
GND
Assuming the impedance of transmission line is 50W the
values of the termination resistors are:
Supply Voltage
+3.3V or -3.3V
R1 (
W)
127
R2 (
W)
83
Supply Voltage
+5.0V or -5.0V
R1 (
W)
83
R2 (
W)
125
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AN1002
HIGH-PERFORMANCE PRODUCTS
SK100EL90W in ECL-to-PECL or LVPECL Mode Configuration
VCC = 0V
VCC = +5V
or +3.3V
GND = 0V
R1
R1
SK100EL90W
R1
VCC
DO
1
2
PECL
ECL
20
V
CC
19
Q0
3
DO*
R2
R2
18
Q0*
VCC = +3.3V or +5.0V
R2
R1
R1
R1
R1
VBB
4
5
ECL
17
GND
16
PECL
VEE = -5.0V
ECL DEVICE
Single Ended
Mode
R2
GND = 0V
R1
PECL /
Q1
D1
LVPECL DEVICE
R2
R2
6
D1*
15
Q1*
GND
R2
R2
VEE = -5.0V
VBB
7
8
14
13
PECL
ECL
GND
GND
Q2
D2
0.1µF
Unused
Input
9
10
12
Q2*
D2*
VEE
-5.0V
GND
11
VCC
VEE = - 5.0V
GND
Assuming the impedance of transmission line is 50W the
values of the termination resistors are:
Supply Voltage
+3.3V or -3.3V
R1 (
W)
127
R2 (
W)
83
Supply Voltage
+5.0V or -5.0V
R1 (
W)
83
R2 (
W)
125
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AN1002
HIGH-PERFORMANCE PRODUCTS
SK100EL91W in LVPECL - to - ECL or LVECL Mode Configuration
VCC = +3.3V
VCC = +3.3V
VCC = +3.3V
R1
R1
VCC = 0V
SK100EL91W
R1
VCC
DO
1
2
LVPECL
ECL
20
V
CC
19
Q0
3
DO*
R2
R2
18
Q0*
R1
R2
GND = 0V
Single Ended
Mode
PECL
_VBB
D1
R1
LVPECL
LVPECL
DEVICE
R1
4
5
ECL
17
GND
16
Q1
R1
R2
VCC= +3.3V
VCC = 0V
R1
ECL / LVECL
DEVICE
6
D1*
15
R2
R2
Q1*
R2
R2
GND = 0V
PECL
_VBB
D2
7
8
LVPECL
14
13
ECL
GND
VEE = - 5.0V
or - 3.3V
VEE = - 5.0V
or - 3.3V
Q2
0.1µF
Unused
Input
9
10
12
Q2*
D2*
VEE
VEE = - 5.0V
or - 3.3V
VCC=+3.3V
11
VCC
VEE= 0V
VEE = - 5.0V
or - 3.3V
Assuming the impedance of transmission line is 50W the
values of the termination resistors are:
Supply Voltage
+3.3V or -3.3V
R1 (
W)
127
R2 (
W)
83
Supply Voltage
+5.0V or -5.0V
R1 (
W)
83
R2 (
W)
125
Revision 1/November 27, 2001
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