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 ]

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.

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 74xx, 74Lxx

74LSxx, 74ALSxx

74ASxx, 74Fxx

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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 74HCTxx, 74AHCTxx

74ACTxx, 74FCTxx

74FACTxx, 74ACTQxx

{Logic Family Voltage Translation Index}

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 74Cxx, 74HCxx

74AHCxx, 74ACxx

74ACQxx

The TTL gate will output between 2.4v [V OH min.] and 3.3v [V OH 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.

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}

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 V OL is lower and the V OH is higher.

74Cxx, 74HCxx

74HCTxxx, 74AHCxx

74AHCTxx, 74ACxx

74ACTxx, 74ACQxx

74ACQTxx, 74FCTxx

74FACTxx 74xx, 74Lxx

74LSxx, 74ALSxx

74ASxx, 74Fxx

{Logic Family Voltage Translation Index}

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 Level Shifter

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}

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 10xxx, 10Kxx

10Hxx, 10Exxx

10EPxx, 10ELxx

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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 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}

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 74xx, 74Lxx

74LSxx, 74ALSxx

74ASxx, 74Fxx

74HCTxxx, 74AHCTxx

74ACTxx, 74ACQTxx

74FCTxx, 74FACTxx 74Cxx, 74HCxx

74HCTxxx, 74AHCxx

74AHCTxx, 74ACxx

74ACTxx, 74ACQxx

74ACQTxx, 74FCTxx

74FACTxx 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.

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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}

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:

V A = V CC – 2v = V CC x [(R2 + R3)/R1 + R2 +R3)]

R AC = R1 // (R2 + (R3 // 50) = 50 Ohms

R DC = 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.

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}

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 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.

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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 74xx, 74Lxx

74LSxx, 74ALSxx

74ASxx, 74Fxx

74HCTxxx, 74AHCTxx

74ACTxx, 74ACQTxx

74FCTxx, 74FACTxx

{Logic Family Voltage Translation Index}

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 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.

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Modified 2/27/12

Copyright © 1998 - 2016 All rights reserved Larry Davis