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Real logic gatesMeasuring voltage limits

ElectronicsLogic Gates: Measuring Voltage Limits

Terry Sturtevant

Wilfrid Laurier University

November 20, 2014

Terry Sturtevant Electronics Logic Gates: Measuring Voltage Limits

Real logic gatesMeasuring voltage limits Reading Data sheets

Input voltages will not always be at ideal values

a range of input values must be considered highanother range of input values must be considered low.Similarly output voltages will not always be at ideal valuesa range of output voltages should be considered as highanother range of output voltages should be considered low.



Input voltages will not always be at ideal valuesa range of input values must be considered high

another range of input values must be considered low.Similarly output voltages will not always be at ideal valuesa range of output voltages should be considered as highanother range of output voltages should be considered low.



Input voltages will not always be at ideal valuesa range of input values must be considered highanother range of input values must be considered low.

Similarly output voltages will not always be at ideal valuesa range of output voltages should be considered as highanother range of output voltages should be considered low.



Input voltages will not always be at ideal valuesa range of input values must be considered highanother range of input values must be considered low.Similarly output voltages will not always be at ideal values

a range of output voltages should be considered as highanother range of output voltages should be considered low.



Input voltages will not always be at ideal valuesa range of input values must be considered highanother range of input values must be considered low.Similarly output voltages will not always be at ideal valuesa range of output voltages should be considered as high

another range of output voltages should be considered low.



Input voltages will not always be at ideal valuesa range of input values must be considered highanother range of input values must be considered low.Similarly output voltages will not always be at ideal valuesa range of output voltages should be considered as highanother range of output voltages should be considered low.



VIHmin

the minimum input voltage which will be accepted as a logic1.VILmax

the maximum input voltage which will be accepted as a logic0.VOHmin

the minimum output voltage representing a logic 1 state.VOLmax

the maximum output voltage representing a logic 0 state.



VIHmin

the minimum input voltage which will be accepted as a logic1.

VILmax






VIHmin







VIHmin


the maximum input voltage which will be accepted as a logic0.

VOHmin





VIHmin







VIHmin



the minimum output voltage representing a logic 1 state.

VOLmax




VIHmin







Reading Data sheets

The actual limits on voltage, current, timing, etc. will begiven in manufacturer’s data sheets.Different manufacturers arrange their data sheets differently,and use different names.



Reading Data sheets

The actual limits on voltage, current, timing, etc. will begiven in manufacturer’s data sheets.

Different manufacturers arrange their data sheets differently,and use different names.



Reading Data sheets

The actual limits on voltage, current, timing, etc. will begiven in manufacturer’s data sheets.Different manufacturers arrange their data sheets differently,and use different names.



Supply voltage Designations

The supply voltages for various families have names which arebased on the type of transistors used in their construction.For instance, TTL gates are made with bipolar transistors,which have a collector and an emitter,the supply voltages are VCC and GROUND is occasionallygiven as VEE.On the other hand, CMOS gates are built with field–effecttransistors which have a drain and a source,the supply voltages are VDD and VSS.




The supply voltages for various families have names which arebased on the type of transistors used in their construction.

For instance, TTL gates are made with bipolar transistors,which have a collector and an emitter,the supply voltages are VCC and GROUND is occasionallygiven as VEE.On the other hand, CMOS gates are built with field–effecttransistors which have a drain and a source,the supply voltages are VDD and VSS.




The supply voltages for various families have names which arebased on the type of transistors used in their construction.For instance, TTL gates are made with bipolar transistors,which have a collector and an emitter,the supply voltages are VCC and GROUND is occasionallygiven as VEE.

On the other hand, CMOS gates are built with field–effecttransistors which have a drain and a source,the supply voltages are VDD and VSS.




The supply voltages for various families have names which arebased on the type of transistors used in their construction.For instance, TTL gates are made with bipolar transistors,which have a collector and an emitter,the supply voltages are VCC and GROUND is occasionallygiven as VEE.On the other hand, CMOS gates are built with field–effecttransistors which have a drain and a source,the supply voltages are VDD and VSS.



Measuring voltage limits

In order to measure the voltage limits, you can connect up thecircuit as in the following figure.



Vcc

Vin

1 2

GND



Using a sine wave input with the oscilloscope operating in the X–Ymode, a trace similar to the one shown in the following figureshould be obtained.

(The output shown is for an LSTTL inverting gate.)



Using a sine wave input with the oscilloscope operating in the X–Ymode, a trace similar to the one shown in the following figureshould be obtained.(The output shown is for an LSTTL inverting gate.)



Vin



Vin

Vout



Vin

Vout

logic “0” input0.8



Vin

Vout


��VOHmin



Vin

Vout




Vin

Vout


��VOLmax



Vin

Vout

logic “0”output

0.5



Vin

Vout

logic “0”output

0.5 ��

VIHmin



Vin

Vout

logic “1”output

2.7



Vin

Vout

logic “1”output

2.7 ��

VILmax



This is called the transfer characteristic of the gate.

Note that the input voltage, Vin, is on the X axis and the outputvoltage, Vout, on the Y axis.



This is called the transfer characteristic of the gate.Note that the input voltage, Vin, is on the X axis and the outputvoltage, Vout, on the Y axis.



Vin

Vout

CMOS will look slightly different.



Measuring Output Voltage Limits

The output voltage produced by an input voltage of thespecified value of VILmax would be the measured value ofVOHmin .The output voltage is produced by an input voltage of thespecified value of VIHmin would be the measured value ofVOLmax .




The output voltage produced by an input voltage of thespecified value of VILmax would be the measured value ofVOHmin .

The output voltage is produced by an input voltage of thespecified value of VIHmin would be the measured value ofVOLmax .




The output voltage produced by an input voltage of thespecified value of VILmax would be the measured value ofVOHmin .The output voltage is produced by an input voltage of thespecified value of VIHmin would be the measured value ofVOLmax .
