Logic Family Voltage Translation


[TTL - TTL ]
[TTL - CMOS {74xxT} ]
[TTL - CMOS {74xx}] [CMOS {74xx} - TTL]
[TTL - CMOS {4xxx}] [CMOS {4xxx} - TTL]
[TTL - ECL] [ECL - TTL] [ECL - CMOS]
[PECL to TTL] [PECL to LVDS] [LVPECL to LVDS]
[TTL - Low Voltage {74LVxx}]
[EIA422 to EIA232]
[Logic Design Page ]


Glue Logic Threshold Levels


Note: except for glue logic IC devices, TTL based devices do not really exist in any other device. All devices [other then glue logic ICs] produced use CMOS devices, and their I/O pins switch at CMOS levels.
However, CMOS devices can be made to switch at TTL, even as they use CMOS devices. See this page for a listing of Glue Logic IC manufacturers.




TTL to TTL Logic

Any of these 5 volt TTL devices {listed on the left} will drive any of the 5 volt TTL devices listed on the right. No translation is needed.
Of course Fan-Out requirements still have to be observed. Fan-Out varies with each different logic family. Fan-Out defines the number of devices an IC can drive.


74xx, 74Lxx
74LSxx, 74ALSxx
74ASxx, 74Fxx

TTL Flip Flop

74xx, 74Lxx
74LSxx, 74ALSxx
74ASxx, 74Fxx



{Back to Logic Family Voltage Translation Index}


TTL to CMOS {74xxT} Logic

Any of these 5 volt TTL devices {listed on the left} will drive any of the 5 volt CMOS devices listed on the right. No translation is needed.
The { T } in the CMOS part number indicates the input switches at TTL levels [the output still switches at CMOS levels]. Chart comparing 5 volt TTL, CMOS Switching Levels


74xx, 74Lxx
74LSxx, 74ALSxx
74ASxx, 74Fxx
CMOS Flip Flop
74HCTxx, 74AHCTxx
74ACTxx, 74FCTxx
74FACTxx, 74ACTQxx

{Logic Family Voltage Translation Index}


TTL to CMOS {74xx} Logic

Any of these 5 volt TTL devices {listed on the left} will drive any of the 5 volt CMOS devices listed on the right. A level switching Pull-Up resistor is required.
A value of between 1K and 2K will work well, the true value depends on the Fan-Out of the TTL gate.
The larger the Fan-Out (the more devices it's driving), the higher the resistor value. Fan-Out varies with each different logic family.


74xx, 74Lxx
74LSxx, 74ALSxx
74ASxx, 74Fxx
TTL to CMOS Flip Flop with Pull-ups
74Cxx, 74HCxx
74AHCxx, 74ACxx
74ACQxx

The TTL gate will output between 2.4v [VOH min.] and 3.3v [VOH max.] for a high level (depending on the logic family).
The CMOS gate requires a minimum of 3.7 volts to register a high. The Pull-Up resistor increases
the output voltage from the TTL driver. The resistor allows the TTL chip to deive a CMOS chip.

T Series Flip Flop

A 74ACTxx series device could be used, instead of the pull-up resistors.
The 'T' CMOS part accepts TTL levels at the input while keeping the output at CMOS levels, and the internal device is still all CMOS [so the current consumption is still very low].
Refer to the TTL to CMOS {74xxT} Logic example.


{Logic Family Voltage Translation Index}


CMOS {74xx} to TTL Logic

Any of these 5 volt CMOS devices {listed on the left} will drive any of the 5 volt TTL devices listed on the right. No translation is needed.
Of course Fan-Out requirements still have to be observed. A 74xx CMOS device will always drive a TTL device, the VOL is lower and the VOH is higher.


74Cxx, 74HCxx
74HCTxxx, 74AHCxx
74AHCTxx, 74ACxx
74ACTxx, 74ACQxx
74ACQTxx, 74FCTxx
74FACTxx
CMOS Flip Flop
74xx, 74Lxx
74LSxx, 74ALSxx
74ASxx, 74Fxx

{Logic Family Voltage Translation Index}


TTL to CMOS {4xxx} Logic

This really depends on the Vcc of the CMOS device, which could be up to+15 volts.
Common power supply voltages for 4000 series logic include 12 volts, 5 volts, or any voltage in between.
A 14504 may be used to shift between 'true' CMOS voltages [5 to 15 volts] and TTL logic levels.
MC14504 Hex Level Shifter for TTL to CMOC or CMOS to CMOS.


CMOS to TTL Level Shifter
CMOS Level Shifter

CMOS {4xxx} to TTL Logic

This really depends on the Vcc of the CMOS device, which could be up to +15 volts.
The MC14504 [above] translates between 3 to 18 volt CMOS levels and TTL input levels.

{Logic Family Voltage Translation Index}


TTL to ECL Logic




A (10124) TTL to ECL translator is used to switch between the two logic families. Only the 10K family is shown,
the same is true for the 100K ECL family.
ECL Termination resistors (not shown) are required between the 10124 and the ECL device. Standard ECL design practices.


74xx, 74Lxx
74LSxx, 74ALSxx
74ASxx, 74Fxx
74Cxx, 74HCxx
74HCTxxx, 74AHCxx
74AHCTxx, 74ACxx
74ACTxx, 74ACQxx
74ACQTxx, 74FCTxx
74FACTxx
TTL to ECL Flip Flop Translation
10xxx, 10Kxx
10Hxx, 10Exxx
10EPxx, 10ELxx

{Logic Family Translation Index}


ECL to TTL Logic

A (10125) ECL to TTL translator is used to switch between the two logic families. Only the 10K family is shown,
the same is true for the 100K ECL family.
ECL Termination resistors (not shown) are required between the ECL and the 10125 device. Standard ECL design practices.



10xxx, 10Hxx
10Exxx, 10EPxx
10ELxx
ECL Flip Flop
74xx, 74Lxx
74LSxx, 74ALSxx
74ASxx, 74Fxx
74HCTxxx, 74AHCTxx
74ACTxx, 74ACQTxx
74FCTxx, 74FACTxx

If the device is CMOS then you require the same pull-up listed above (TTL to CMOS). A resistor between 1K and 2K ohms.


{Logic Family Voltage Translation Index}


PECL to TTL / TTL to PECL Logic

In this case PECL= Positive ECL
A (10350) PECL to TTL translator is used to switch between the two logic families. Only the 10K family is shown, the same
is true for the 100K ECL family. PECL switches to +3.2v for a low, and +4.1v for a high.



10xxx, 10Hxx
10Exxx, 10EPxx
10ELxx
PECL 10350 Flip Flop
74xx, 74Lxx
74LSxx, 74ALSxx
74ASxx, 74Fxx
74HCTxxx, 74AHCTxx
74ACTxx, 74ACQTxx
74FCTxx, 74FACTxx
74Cxx, 74HCxx
74HCTxxx, 74AHCxx
74AHCTxx, 74ACxx
74ACTxx, 74ACQxx
74ACQTxx, 74FCTxx
74FACTxx
PECL 10351 Flip Flop
10xxx, 10Hxx
10Exxx, 10EPxx
10ELxx

A (10351) TTL to PECL translator is used to switch between the two logic families. Only the 10K family is shown,
the same is true for the 100K ECL family.
If the device is CMOS then you require the same pull-up listed above (TTL to CMOS). Between 1K and 2K ohms.


{Logic Family Voltage Translation Index}



PECL to LVDS

PECL to LVDS Translation

Both LVPECL and LVDS are differential voltage standards, but they use different transceivers and switch at different levels.
The voltage levels have to be translated. For detailed EIA644 [LVDS] design information see the LVDS description page

{Back to Logic Family Voltage Translation Index}



LVPECL to LVDS

LVPECL Signal Conversion to LVDS

The graphic above only shows one end of the differential pair. The resistors need to be added to both pairs.
Equations for calculating the resistors in the figure above:
VA = VCC – 2v = VCC x [(R2 + R3)/R1 + R2 +R3)]
RAC = R1 // (R2 + (R3 // 50) = 50 Ohms
RDC = R1 // (R2 + R3) ~ 50 Ohms
Gain = (R3 // 50) / (R2 + (R3 // 50) > 0.17
3.3v / 275 ohms = 12mA or 6.8mW, so a 1/16 watt resistor will do.

LVPECL to LVDS converter circuit

Both LVPECL and LVDS are differential devices, but they switch at different levels. The voltage levels have to be translated.
This circuit just shifts the voltage. LVPECL is PECL that switches at 3.3 volts instead of 5 volts.
For detailed EIA644 [LVDS] bus description, see this LVDS description page

{Back to Logic Family Voltage Translation Index}


ECL to CMOS Logic

A (10125) ECL to TTL translator is used to switch between the two logic families. Only the 10K family is shown,
the same is true for the 100K ECL family.
ECL Termination resistors (not shown) are required between the ECL and the 10125 device.
Standard ECL design practices.
In addition, a TTL to CMOS translator is required


10xxx, 10Hxx
10Exxx, 10EPxx
10ELxx
ECL 10125 Flip Flop
74xx, 74Lxx
74LSxx, 74ALSxx
74ASxx, 74Fxx
74Cxx, 74HCxx
74HCTxxx, 74AHCxx
74AHCTxx, 74ACxx
74ACTxx, 74ACQxx
74ACQTxx, 74FCTxx
74FACTxx

Pull-up resistors could be used instead of the TTL - CMOS translator listed above. The resistor should be between 1K and 2K ohms.


{Logic Family Voltage Translation Index}


Low Voltage {74LVxx} 3.3volt Logic

A (74LVC4245) Bidirectional 3.3v to 5volt transceiver is used to switch between the two logic families.
Bus "B" is the TTL +5volts side, Bus "A" is the +3.3volt side.


74LVxx, 74LVCxx
74LVTxx, 74LVTZxx
74LVCHxx, 74ALVCxx
74LCxx
Low Voltage Flip Flop
74xx, 74Lxx
74LSxx, 74ALSxx
74ASxx, 74Fxx
74HCTxxx, 74AHCTxx
74ACTxx, 74ACQTxx
74FCTxx, 74FACTxx

{Logic Family Voltage Translation Index}



EIA422 to EIA232

RS422 to RS232 circuit translation




EIA422 is a differential [two wire] bus, while RS232 is single wire. EIA422 sends data out as its 'true; and 'complement' value over two wires.
For a detailed RS422 interface bus description and information see the RS422 Bus page
For detailed RS232 Bus design information refer to that page.

{Logic Family Voltage Translation Index}



Generic Level Shifter

A number of ICs will perform a level shift.
One example is the 40109 CMOS Quad Low-to-High Voltage Level Shifter

40109 CMOS Level Translater
40109 CMOS Level Shifter

Using different voltages for Vcc and VDD, the 40109 will up-shift or down-shift a signal.
The supply voltages may range from 3 volts to 18 volts
The 40109 acts as an up-shifter if VDD is greater than VCC, or a down-shifter if VCC is greater.
There are three common voltages used in the data sheet; 5v, 10v and 15 volts.
But the voltages are only provided as a reference for propagation delays or other IC characteristics.
The output of the 40109 is taken between a dual MOSFET totem pole arrangement.
The top FET is connected to the supply rail VDD, and the bottom is taken to ground [Vss].

See this page for a listing of Glue Logic manufacturers.

{Back to Logic Family Voltage Translation Index}


PC motherboard
Home

Distributor rolodex Electronic Components Electronic Equipment EDA CDROM Software Engineering Standards, BOB card Cabled Computer Bus Electronic Engineering Design Table Conversion DB9-to-DB25.
DistributorsComponents Equipment Software Standards Buses Design Reference

Modified 2/27/12
Copyright © 1998 - 2012 All rights reserved Leroy Davis