Semiconductor Components Industries, LLC, 2004
November, 2004 − Rev. 9 1Publication Order Number:
AN1672/D
AN1672/D
The ECL Translator Guide
PECL • LVPECL • NECL • TTL •
LVTTL/LVCMOS • CMOS
Prepared by: Paul Shockman
ON Semiconductor
Objective
This application note is intended to provide the basic
device selection and connection information to enable signal
translation interface between ON Semiconductor’s ECL
logic operating in various supply modes This document also
provides information regarding translation between our
ECL devices and TTL (5 V), CMOS (5 V), or
LVTTL/LVCMOS (3.3 V) devices. For translation interface
with LVDS, see AN1568.
Translation to and from ECL technology is discussed in
three section divisions:
Section 1. Translation between differently supplied
ECL drivers and receivers
Section 2. Translation from different ECL operating
mode drivers to non ECL receivers
Section 3. Translation from non ECL drivers to
different ECL operating mode receivers
Proper translation occurs when the driver ’s output logic
levels are within the spec limits of the receiver and are
recognized. Specific device data sheets should be consulted
for exact specifications and parameter limits.
Resources
IBIS and SPICE models may be found at
www.onsemi.com for most devices. General ECL
information, also online, may be consulted such as
AND8020, AND8066, and AND8072.
General Background
TTL and CMOS drivers generally source current (to the
receiver) in the HIGH state and sink current (from the
receiver) in the LOW state. In contrast, ECL drivers source
current in both HIGH and LOW states (to the receiver).
Receiver inputs do not require any “termination” although
any driver may or may not require termination
considerations. The driver termination considerations may
be located physically near or internal to a receiver.
TTL and CMOS devices will usually be operated across
a single positive power supply (VCC or VDD) and ground.
ECL devices may operate similarly across a single Positive
supply and VEE (Ground) as Positive ECL (PECL) or Low
Voltage Positive ECL (LVPECL). Or traditionally, ECL
devices may span across Ground and a single negative
power supply, VEE, as Negative ECL (NECL) or Low
Voltage Negative ECL (LVNECL). Any device may be
operated with all pins offset by a fixed voltage, but interface
with standard levels may require a translation device. A pure
ECL device might be operated in NECL, PECL, or LVPECL
mode by simply shifting all voltage levels. Of course, a
translator dedicated to a specific technology will expect only
fixed voltages and can’t usually operate in different, or
shifted voltage modes.
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Different ECL operating supply modes are generally
considered to be as presented below in Table 1.
Table 1. ECL Operating Supply Modes
PECL VCC = 5.0, VEE = 0.0
LVPECL VCC = 3.3, VEE = 0.0
2.5VPECL VCC = 2.5, VEE = 0.0
2.5VNECL VCC = 0.0, VEE = −2.5
LVNECL VCC = 0.0, VEE = −3.3
NECL VCC = 0.0, VEE = −5.0
Some devices may span one or more operating modes and
each mode will allow supply tolerances. ECL signal levels
(VOL, VOH, VIL, and VIH) are referenced from the VCC pin
or positive rail. Therefore, when ECL devices are operated
from different negative power supplies, no translation is
required for interconnects. When operated in a single ended
configuration, the critical Input parameters are VIL and VIH
limits (VIHCMR and Vpp are ignored). When operation
differentially, critical limit Input parameters are VIHCMR
and Vpp (VIL and VIH are ignored). See AND8066 for
interconnect details. All supply pins, VCC, LVCC, and
GND, must be connected for proper operation. A 0.1 F to
0.01 F decoupling cap is recommended from VCC to GND.
VCC ripple should be minimized and may require additional
filter networks.
Standard non ECL operating modes are generally
considered ( with c ertain s upply t olerances) t o b e a s p resented
below in Table 2.
Table 2. Non ECL Operating Supply Modes
VCC = 5.0, VEE = 0.0
VCC = 3.3, VEE = 0.0
VCC = 2.5, VEE = 0.0
Most translation interface between technologies will
require a separate, dedicated translator IC device, but some
newer ECL devices offer a translation feature integrated into
certain mode control pins. Several of the GigaComm
devices offer a programmable mode pins for selecting the
control pins translation levels. MC10EP195 offers Delay
Select pins with user programmable TTL, CMOS, or ECL
threshold levels.
An alternative translation technique, cap coupling, is
discussed in Application Note AND8020, Section 5. Cap
coupling may accommodate level shifting when the signal’s
“edge density” is sufficient. Otherwise, coding may be
required to increase ”edge density”. Certainly the risk of
erroneous levels, due to the coupling cap leakage, may not
be acceptable and system requirements may demand the
hard levels found with active device translation.
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Section 1: Translation Between Differently Supplied ECL Drivers and Receivers
Table 3. Translation Between Differently Supplied ECL Drivers and Receivers
To:
From: PECL
VCC = +5 V LVPECL
VCC = +3.3 V LVNECL
VEE = −3.3 V NECL
VEE = −4.5 to −5.2 V
PECL
VCC = +5 V Standard Connection LVEL92 LVEL91 EL91
LVPECL
VCC = +3.3 V EL17
EP17
LVEL16
LVEL17
Direct Connection LVEL91
LVEP91 LVEP91
LVNECL
VEE = −3.3 V EL90 LVEL90 Standard Connection Direct Connection
NECL
VEE = −4.5 V to −5.2 V EL90 LVEL90 Standard Connection Standard Connection
From PECL to LVPECL
The MC100LVEL92 translates signals from a PECL
(VCC = 5.0, V EE = 0.0) operating mode driver to a LVPECL
VCC = 3.3, VEE = 0.0 operating mode receiver.
From PECL to NECL
The MC100EL91 translates signals from a PECL
(VCC = 5.0, VEE = 0.0) operating mode driver to a NECL
(VCC = 0.0, VEE = −5.0) operating mode receiver.
From PECL to LVNECL
The MC100LVEL91 translates signals from a PECL
(VCC = 5.0, V EE = 0.0) operating mode driver to a LVNECL
(VCC = 0.0, VEE = −3.3) operating mode receiver.
From LVPECL to PECL
The critical parameter for differential PECL receiver to
properly interface with a differential LVPECL driver is
VIHCMRmin (or VCMRmin). VIH and VIL limits may be
disregarded for differential receiving. Assuming no tangent
loss from traces, if the LVPECL driver VOHmin level is more
positive (higher) than the VIHCMRmin spec of the differential
PECL receiver, the device will properly translate or level
shift from LVPECL to PECL. For example, suppose a
MC100EP16 operating differentially in LVPECL mode
(VCC = 3.3, V EE = 0.0) with a worst case VOHmin of 2.155 V,
drives a MC100EP17 receiver differentially operating in
PECL mode (VCC = 5.0, VEE = 0.0). The MC100EP17
receiver spec VIHCMRmin is 2.0 V and will always properly
recognize the drivers HIGH level 2.155 V (or higher). The
MC100EL13, MC100EL14, MC100EL29, MC100EL56
are also acceptable as LVPECL receivers differentially.
Most of the “E” (ECLinPS), “EL” (ECLinPS Lite),
10H/100H, or 10xxx series devices do not have a
sufficiently low VIHCMRmin to receive LVPECL.
When a receiver in LVPECL mode is driven single ended,
the critical parameters will be VIL and VIH. VIHCMRmin (or
VCMRmin) may be ignored. A PECL receiver VILmin,
typically >3.0 V, will be insufficiently low to recognize the
drivers HIGH level and will not permit proper interconnect.
From LVPECL to LVNECL
The MC100LVEL91 translates signals from a PECL
(VCC = 5.0, VEE = 0.0) operating mode driver to a
LVNECL (V CC = 0.0, VEE = −3.3) operating mode receiver .
From LVPECL to NECL
The MC100EL91 translates signals from a LVPECL
(VCC = 3.3, VEE = 0.0) operating mode driver to a NECL
(VCC = 0.0, VEE = −5.0) operating mode receiver.
From LVNECL to PECL
The MC100EL90 translates signals from a LVNECL
(VCC = 0.0, VEE = −3.3) operating mode driver to a PECL
(VCC = 5.0, VEE = 0.0) operating mode receiver.
From LVNECL to LVPECL
The MC100LVEL90 translates signals from a LVNECL
(VCC = 0.0, VEE = −3.3) operating mode driver to a PECL
(VCC = 3.3, VEE = 0.0) operating mode receiver.
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Section 2: Translation from Different ECL Operating Mode Drivers to Non ECL Receivers
The following table indicates the options available for translation from different ECL operating drivers to non ECL receivers.
Table 4. Translation from Different ECL Operating Mode Drivers to Non ECL Receivers
To:
From: TTL
VCC = +5 V LVTTL/LVCMOS
VCC = 3.3 V CMOS
VDD = 5 V
PECL
VCC = +5 V H350
H607
ELT21
ELT23
ELT28*
LVEL92 + LVELT23
or EPT21
or EPT23
or LVELT23
or EPT26
PECL to TTL or PECL to LVTTL/LVCMOS
Translator and HCT or ACT
LVPECL
VCC = +3.3 V ELT21
ELT23 EPT21
EPT23
LVELT23
EPT26
LVPECL to LVTTL Translator and
HCT or ACT Input
LVNECL
VEE = −3.3 V ELT25
EPT25* EPT25 LVNECL/TTL Translator to HCT or
ACT Input
NECL
VEE = −4.5 to −5.2 V H125
H601
H603
H605
H680*
H681*
ELT25
EPT25*
EPT25 NECL/TTL Translator to HCT or
ACT Input
*See text segment for details
From PECL to TTL
MC10H350 as PECL to TTL
Several devices are offered for translation signals from
PECL mode drivers to 5 V supplied TTL receivers. The
MC10H350 operates over the frequency range from DC to
about 50 MHz. Although operation is possible to 80 MHz,
the output will not sustain full spec VOH levels rolling off
with higher frequency.
Open, floating differential inputs on a gate will force the
TTL output to default LOW. By adding a pullup resistor of
1 k to 4 k, a device’s output will directly interface with
CMOS (5 V) inputs. The device input pin “common mode
range”, VIHCMR min to max, is insufficient to allow
recognition of LVPECL levels. Single ended operation of
the MC10H350 will require an input signal swing of 700 mV
peak−to−peak or greater.
Outputs are Enabled by Pin 9, OE, going LOW. If left
floating open, MC10H350 Pin 9 will default LOW. Worst
case skew from Output to Output within a device occurs
from Input falling edge to Output falling edge at 125°C at
1.4 ns. For the Input rising edge to Output rising edge, the
worst case skew is about 1 ns (at −55°C). Device to Device
slew is less than 800 ps skew from part to part. Output drive
will come out of saturation with 80 mA − 100 mA, lowering
VOH levels.
MC10H607 / MC100H607 as PECL to TTL
The MC10H607 and MC100H607 are Registered PECL
to TTL translators. A standard output test condition load is
50 pF and 500 to GND. MR, Pin 19, will default LOW
when floating open, allowing operation. The input pin
“common mode” range is insufficient to allow recognition
of LVPECL levels.
ELT21/23/28 as PECL to TTL
ECL inputs for ELT21/23/28 have 50 k internal
pulldown resistors. If both ECL ELT21/23 inputs are pulled
below 1.3 V, an override circuit will force the output Q to
HIGH, Qb L O W. B y adding an output pullup resistor of 1 to
4 k, a device will interface with CMOS (5 V) inputs. The
input common mode range for ELT21 / ELT23 is generally
considered to be sufficient (2.2 V) to allow recognition of
PECL HIGH levels (>4 V) allowing translation. Single
ended operation may be accomplished with a VBB reference
voltage placed on the nondriven differential input. If a VBB
pin is present, then it should be bypassed when used or left
floating open when unused. A simple VBB supply may be
created by a resistor divider providing the proper switch
point voltage to preserve duty cycle (see AND8066). A
High Current may be created from a simple buffer gate as
shown in AND8020, Figure 22.
These ELT TTL devices typically display >2X the
required data sheet drive. For example, at VOLmax (0.5 V)
the required sinking drive current is 24 mA and actual drive
>>50 mA. At VOHmin (2.4 V), the spec sourcing drive
current is 3.0 mA and the typical device will source >>8 mA.
The unloaded VOH max may reach as positive as 4.0 V.
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Typical drive current strength of the TTL output is shown in the following two tables, Table 5 and Table 6, and their graphs,
Figure 1 and Figure 2.
Table 5. ELT TTL Series Drive LOW Current (IOL) vs
Voltage (VOL)
IOL VOL
0.010 0.162
0.020 0.209
0.030 0.256
0.040 0.303
0.079 0.465
0.118 0.628
Figure 1. ELT TTL Series Drive LOW Current (IOL)
versus Voltage (VOL)
0.1 0.2 0.3 0.40 0.5 0.6 0.7
VOL (V)
IOL (mA)
0
0.04
0.02
0.08
0.06
0.12
0.10
Table 6. ELT Series TTL Drive HIGH Current (IOH) vs
Voltage (VOH)
IOH VOH
−0.0379 2
−0.0316 2.26
−0.0249 2.508
−0.0164 2.9
−0.0091 3.167
−0.0031 3.339
−0.001 3.4
Figure 2. ELT Series TTL Drive HIGH Current (IOH)
versus Voltage (VOL)
2.52 3 3.5
VOH (V)
IOH (mA)
0
−0.01
−0.02
−0.04
−0.03
Typical ELT TTL series output impedance in the HIGH
state is about 43 . In the LOW state output impedance is
about 42 .
Typical tPLH and tPHL may differ as much as 0.5 ns. At
higher frequencies, the output swing will decrease. Gain is
typically about five and inputs require a minimum of
200 mVpp swing. Jitter is typically 500 ps. Measurements
are made at 1.5 V for AC characteristics such as tpd and
skew.
From PECL to LVTTL
This translation requires two devices for a direct, active
connection. First, a level shift from PECL to LVPECL is
done with the MC100LVEL92. Then, a translation from
LVPECL to LVTTL is done with either the LVELT23,
EPT21, EPT23, LVELT23, or EPT26 (see segment below).
No sequencing is needed in powering up the
MC100LVEL92, although both Positive supply levels, VCC
and LVCC, must be connected for proper operation.
From PECL to CMOS
The translation from PECL to CMOS is accomplished
through two stages, from PECL to an intermediary stage
(such as either TTL or LVTTL), then from the intermediary
stage to CMOS. When the intermediary stage is through
TTL, then the final stage will be from TTL to CMOS using
any of the HCT type devices (i.e., MC74HCT245A), or
ACT (i.e., MC74ACT244).
From LVPECL to TTL
Translation from LVPECL to TTL will be similar to
“PECL to LVTTL” and the prior segment should be
reviewed. The input common mode range maximum (2.2 V)
for ELT21 / ELT23 is generally considered to be sufficient
to allow recognition of LVPECL HIGH levels (>2.2 V), thus
allowing proper translation.
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From LVPECL to LVTTL/LVCMOS
Devices MC100EPT21, MC100EPT23, MC100LVELT23,
and MC100EPT26 translate LVPECL signals to
LVTTL/LVCMOS. Standard levels for the LVTTL and
LVCMOS are the same.
There are no “open input” default circuits to force the
outputs to a determined state. Provisions should be taken to
prevent auto−oscillation. If the inputs are permitted to
converged on the same voltage (within the VIHCMR range),
or merely left floating, auto−oscillation will initiate.
There are no powerup sequence requirements or power
sequence restrictions. If either V CC or VEE supplies are not
present, such as during an open pin condition, the output
falls to near zero without harm or damage to the device.
Outputs of these devices typically display about 2X the
required data sheet drive. For example, at VOLmin the drive
is required to sink 24 mA and will typically sink >50 mA. At
VOH, the spec drive is −3.0 mA and will typically source
>8 mA.
Typical drive current strength of the TTL output is shown
in the following two tables, Table 7 and Table 8, and their
graphs, Figure 3 and Figure 4.
Typical EPT TTL series output impedance in the HIGH state is about 5 . In the LOW state output impedance is about 15 .AC
measurements are made to the 1.5 V point for the AC characteristics such as tpd and skew.
Table 7. EPT TTL Series Drive LOW Current (IOL) vs
Voltage (VOL) at 25C
Iout Vout
0.004 0.022
0.020 0.104
0.039 0.200
0.058 0.295
0.082 0.415
0.118 0.596
0.158 0.800
0.1963 1.000
Table 8. EPT Series TTL Drive HIGH Current (IOH) vs
Voltage (VOH) at 25C
Iout Vout
−0.0146 2.32
−0.0112 2.36
−0.0081 2.40
−0.0052 2.44
−0.0028 2.48
−0.0011 2.52
−0.0003 2.56
Figure 3. EPT TTL Series Drive LOW Current (IOL)
versus Voltage (VOL) at 25C
0.2 0.4 0.60 0.8 1
VOL (V)
IOL (mA)
0
0.04
0.08
0.20
0.12
0.16
25°C
Figure 4. EPT Series TTL Drive HIGH Current (IOH)
versus Voltage (VOH)
2.32 2.36 2.4 2.442.3 2.48 2.52 2.56
VOH (V)
IOH
(
mA
)
0
−0.004
−0.008
−0.016
−0.012
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From LVPECL to CMOS
Translation from LVPECL to CMOS will be similar to
“PECL to CMOS” and that prior segment should be
reviewed. The receiver input common mode range
maximum must be sufficient to allow proper recognition of
LVPECL HIGH levels (>2.2 V), thus allowing proper
translation.
The LVPECL to CMOS translation is accomplished
through two stages, first LVPECL to LVTTL, then from
LVTTL to CMOS. Final stage devices may any of the HCT
type devices (i.e., MC74HCT245A), or ACT (i.e.,
MC74ACT244).
From LVNECL to TTL
MC100ELT25 will translate from LVNECL to TTL. Note
the VIHCMR minimum is VEE + 2.2 V. If a 3.3 V supply is
available for the MC100EPT25, this device will translate
LVNECL to TTL, reaching a VOH of greater than 2.4 V up
to 250 MHz.
From LVNECL to LVTTL/LVCMOS
MC100EPT25 will translate from LVNECL to
LVTTL/LVCMOS.
From LVNECL to CMOS
Use a first stage of MC100ELT25 (or MC100EPT23 if a
3.3 V supply is available) and then use a final stage device
of an appropriate HCT (i.e., MC74HCT245A) or ACT (i.e.,
MC74ACT244).
From NECL to TTL
Several devices are offered for translation signals from
NECL mode drivers to 5 V supplied TTL receivers, but the
MC10H125 is the standard translator. Special advantages
may be realized with the MC10H6xx series devices. Review
the device data sheets for specific devices features.
The MC10H125 operates over the frequency range from
DC to about 50 MHz, although operation is possible
>80 MHz with diminished output swing (reduced VOH
levels) with higher frequency. Open, floating differential
inputs on a gate may allow the device to spontaneously auto
oscillate unless provisions are taken to prevent the inputs
from converging. An external network may be used to force
a default state on the outputs when the inputs are open. Use
a 50 k pulldown on the noninverting input, then a 50 k
pullup and a 50 k pulldown on the inverting input.
If a 3.3 V VCC is available, the MC100EPT25 may be used
on this supply to receive NECL and drive a TTL receiver.
The MC100EPT25 VOH will be limited to about 2.6 V at
lower frequencies, decreasing at higher frequencies to 1.6 V
VOH, at 550 MHz (see data sheet). These may be sufficient
levels for a TTL receiver.
From NECL to LVTTL/LVCMOS
MC100EPT25 will translate from NECL to
LVTTL/LVCMOS.
From NECL to CMOS
Use a MC100EPT25 to translate from NECL to
LVTTL/LVCMOS, and then any of the HCT type devices
(i.e., MC74HCT245A), or ACT (i.e., MC74ACT244) to
boost the levels to CMOS.
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Section 3: Translation from Non ECL Drivers to Different ECL Operating Mode Receivers
Table 9. Translation from Non ECL Drivers to Different ECL Operating Mode Receivers
To:
From: PECL
VCC = +5 V LVPECL
VCC = +2.5 V LVPECL
VCC = +3.3 V LVNECL
VEE = −3.3 V NECL
VEE = −4.5 to −5.2 V
TTL H351
H606
ELT20
ELT22
ELT28*
ELT20, or
ELT22, + LVEL92;
if VIH is limited to
VCC = 3.3 V use EPT20,
EPT22, or LVELT22
ELT20 or
ELT22 + LVEL91 H424
H124
H600
H602
H604
ELT24
LVTTL/LVCMOS/
HSTL/CML/LVDS
VCC = 2.5 V
NB100LVEP91 NB100LVEP91 NB100LVEP91
LVTTL/LVCMOS
VCC = 3.3 V H351
H606
ELT20
ELT22
ELT28*
OR:
(EPT20 or EPT22 or EP24
or LVELT22) + 5 V PECL
line receiver
EPT20
EPT22
LVELT22
MC100EPT622
EPT24 or
NB100LVEP91 NB100LVEP91 or
EPT24 + EL91
CMOS
VDD = +5 V H352
ELT20
ELT22
ELT28
H352
+
LVEL92
H352
+
LVEL91
H352
+
EL91
*Bidirectional
From TTL to PECL
An open, floating TTL input will drift to near VCC and
may inject noise into the device under this condition. It is
recommended to tie any unused TTL input to VCC.
MC10H351 as TTL to PECL
The MC10H351 operates over the frequency range from
DC to >200 MHz. Although operation to higher frequencies
is possible, the output VOH levels will decrease, rolling off
as frequency increases. TTL VCC (Pin 11) would best be
connected to the TTL logic devices positive supply, while
ECL V CC is recommended to be isolated to a separate PECL
logic plane, if possible. VEE, Pin 8, may be connected to the
common ground plane.
An open, floating TTL input (Pins 7, 8, 9, 12, 14) will drift
to near VCC and considerations must be taken to reduce
noise injected into the device under this condition, such as
connecting unused inputs to VCC. The Common Strobe pin
is TTL type input.
Output to output skew is 150 ps worst case (at +70°C).
Device to Device slew is less than 300 ps skew. Jitter is 40
to 60 ps.
MC10H606 / MC100H606 as TTL to PECL
This device offers translation and registration
(reclocking) of TTL signals to PECL. Special advantages
may be realized with this device, consult the device data
sheets for specific features.
MC10ELT20 / MC100ELT20 and MC10ELT22 /
MC100ELT22 as TTL to PECL
These devices do not sport any internal input resistor
network to force a default level on an open floating pin. An
open, floating TTL input (Pins 7, 8, 9, 12, 14) will drift to
near VCC and considerations must be taken to reduce noise
injected into the device under this condition, such as
connecting unused inputs to VCC.
Higher operating frequency range will be affected by
input swing; a higher input swing will allow a higher
operating range.
From TTL to LVPECL
Translation from TTL to LVPECL requires a two−stage
process: first TTL to PECL (with a 5 V supply) second
PECL to LVPECL. The first may be accomplished per the
segment above on TTL to PECL. The second stage is done
with MC100LVEL92 (see also PECL t o LVPECL segment).
Under the condition where the TTL signal is confined to
not exceed 3.3 V, a MC10EPT20 / MC100EPT20,
MC10EPT22 / MC100EPT22, or MC100LVELT22 may be
used. The MC100LVELT22 has operation frequency band
range from <1 Hz (with sufficiently sharp edges) to
600 MHz. Diode clamping may be used to prevent input
signals from exceeding 3.3 VCC.
From TTL to LVNECL
Translation from TTL to LVNECL is done in two stages:
1. Use TTL to PECL (ELT20 or ELT22)
2. Then use PECL to LVNECL Translation (LVEL91).
Both are described above. Alternatively, the first
translation may be TTL to LVPECL and the second
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translation would then be LVPECL to LVNECL Translation,
still using the LVEL91.
If a −5 V supply is available, signals may be translated to
NECL ( see n ext s egment) t hen p orted t o a ny LVNECL i nput.
From TTL to NECL
Several devices are available to accomplish TTL to NECL
translation in a single package: the −H424, −H124, and the
ELT24. Alternatively, translation from TTL to NECL could
be done in two stages: first TTL to PECL (ELT20 or ELT22),
second by passing though a PECL to NECL Translation
(EL91). The NECL or LVNECL output levels could then be
ported to any NECL or LVNECL receiver, since the levels
are the same. No power supply sequencing is needed, but all
supply connections are required for proper operation.
H424 as TTL to NECL
An “open”, floating TTL input will drift to near VCC and
considerations and may inject noise into the device under
this condition. It is recommended to tie any unused TTL
input to VCC.
H124 as TTL to NECL
Although n o supply sequencing is required, if the VEE and
GND are powered up prior to the VCC connected, about 5 to
10 mA may be drawn from a “off” VCC supply. This could
draw the off VCC supply to −0.25 V, depending in the internal
“off” impedance.
H600 as TTL to NECL
This device boasts a 9 bit wide capability with a
bandwidth from <1 Hz (with sufficiently sharp edges) to
250 MHz. The ECL Enable input has an internal 50 k
pulldown resistor to force an input default (LOW) state
when floating open. When both the TTL and ECL Enable
pins are forced LOW, the outputs will default to LOW.
H602 as TTL to NECL
This device has similarities to the −H600 with pulldown
resistors on the ENECL, LEN, and MR inputs.
ELT24 as TTL to NECL
Use the MC100EPT24D with a VEE “stand−of f” resistor
of about 61 to drop the 1.7 V difference between VEE of
LVPECL and PECL (mean IEE = 28 mA, sigma = 0.2 mA).
This reduces the operating voltage across the device from
5.0 V VEE supply to 3.3 V.
This device does not have an internal input resistor
network to force a default level on an open, floating input
pin. If floated open, the TTL input, Pin 2, will drift to near
VCC and may inject noise into the device. A 10 k pullup
resistor may be connected from Pin 2 to VCC forcing a
default state (Q HIGH) under open or floating input
conditions.
From LVTTL/LVCMOS to PECL
Translation from LVTTL to PECL may be done in a single
device such as the H351, H606, ELT20, ELT22, or through
half of the ELT28.
For higher frequency operation, translation is done in two
stages:
1. LVTTL to LVPECL using EPT20, EPT22,
LVELT22, or EPT24
2. LVPECL signals into any PECL line receiver with
a VIHCMRmin able to recognize a LVPECL HIGH
level (such as EL17, EL14, EL13, etc.).
From LVTTL/LVCMOS to LVPECL
Use EPT20, EPT22, or LVELT22 to translate from
LVTTL/LVCMOS to LVPECL
From LVTTL to LVNECL
Use the MC100EPT24D
From LVTTL to NECL
Translation from LVTTL/LVCMOS to NECL is done in two
stages:
1. Use LVTTL/LVCMOS to LVPECL (EPT20,
EPT22, LVELT22)
2. Then use LVPECL to NECL (EL91).
From CMOS to PECL
The MC10H352 offers inputs with proper CMOS detect
levels for translating 5.0 V CMOS signals to PECL levels.
Non CMOS detect level devices may be used such as
ELT20, ELT22, and ELT28 for expended frequency range
with some small loss in duty cycle.
From CMOS to LVPECL
Translation from CMOS to LVPECL is done in two stages:
1. CMOS to PECL using a MC10H352 (or similar)
2. Then use a PECL to LVPECL translator,
MC100LVEL92.
From CMOS to LVNECL
T ranslation from CMOS to LVNECL is done in two stages:
1. CMOS to PECL using a MC10H352 (or similar)
2. Then use PECL to LVNECL via MC100LVEL91.
From CMOS to NECL
Translation from CMOS to NECL is done in two stages:
1. CMOS to PECL using a MC10H352 (or similar);
2. Then use PECL to NECL translator, MC100EL91.
AN1672/D
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