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emitter coupled logic


emitter coupled logic



emitter coupled logic definition



Hi Hello Guys , You are here that means you are so exciting about know the principle of the Emitter coupled logic.

Here we represented some of the all the basic funda and detail information about the emitter coupled logic - ECL family.

So Without wasting of your time i am starting the full detailed article about the Emitter coupled logic.

What is electronics switching devices ?


It is also used in the electronics and electrical engineering which deals with the design, control, computation and integration of nonlinear, time-varying energy-processing electronic systems with fast dynamics.


Many time ago in Electronics device mercury arc valves are used. but today modern time in the electronics switch some of the Diodes , transistor, thyristors are used.


Mostly these type of switch used in the AC/DC converter (rectifier).most of all the these device are used in the electricity transmission and its control process.




For more detail guide of Basic of electronic switching devices



Which is Fastest electronics device ?



You all are know that the MOSFET is the fastest switching devices.


Simply we called MOSFET in electronics Language then it is the metal oxide semiconductor field effect transistor.


It has Some of the ability to the change conductivity by the amount of the applied voltage.


Mosfet is the four terminal devices.they are like Source(S) , Gate(G) , Drain (D) and Body (B) terminals.


If you check in the electrical circuit then only appears three terminals.

For more detail guide on fastest electronics switching device mosfet



Basic Of  Emitter coupled logic(ECL)



In electronics family Emitter coupled logic (ECL) is the high speed integrated circuit bipolar transistor.

ECL is used as overdriven BJT differential Amplifier.It has single ended input and Limited emitter current to avoid from the saturated region of the operation.

And its has slow turn off behavior.

Here current is flow in two legs of emitter coupled pair.ECL is also sometimes called as the current steering logic (CSL) , Current mode logic (CML) , current switch emitter follower (CSEF) logic.

We already talk that Transistors are never in saturation region , its input and output voltages have very small swing like 0.8.

We all know that its input impedance is high and its output impedance is low.

You know that transistor is switching device and transistor is quickly change its state.


Its Fanout capabilities is high.it is essentially constant current draw of the differential amplifiers.


It is the decrease the propagation  time of the whole circuit by reducing inverter count.


If you ask about different electronics switching devices like Mosfet , IGBT , Transistor , GTO , Diac , Triac etc..

IF you curious to know about the MOSFET as the Fastest switching devices then go for .....


History of emitter coupled logic(ECL)



Emitter coupled logic was invented in August 1956 at IBM by Hannon s.Yourke.Its also called as current-steering logic.Its logic also called as current mode circuit.

It is also used in the make ASLT circuit in IBM.

In this differential amplifiers Whose input logic levels were different from the output logic levels.

In the beginning of the  1960 ECL circuit were implemented on monolithic integrated circuits.

First Monolithic circuits is Introduced by the Motorola in 1962. Also Motorola developed several improved series in 1966.

Which has 1 nanosecond gate propagation time and which has 300 MHZ flip-flop  toggle rates.

The ECLinPS family is introduced in the 1987.

Now we talk about the GATE delay then 500 ps single gate delay and it has 1.1 GHZ flip-flop toggle frequency.

ECl has High power Consumption So its used is mainly for the High speed requirement.





Basic Circuit Diagram of emitter coupled logic(ECL)


emitter coupled logic tutorial


positive emitter coupled logic


image credit wikipedia  

                                                           emitter coupled logic circuit




ECL is devised which is based on the emitter coupled pair.For The Detail Shown in the above figure.


Shown in figure that left half of the pair which has two parallel-connected input transistors T1 and T2.And Input NOR Logic is used.


Shown on figure that on the right T1 And T2 Transistor T3 is provided which based voltage is fixed by a reference voltage source.


In shaded light green voltage divider with diode thermal compensation (R1,R2 and D1,D2) And also buffering emitter follower.


Emitter voltage is kept relatively steady.Re is the common emitter resistance which work like current source.


output voltage of the collector load here resistors Rc1 and Rc3 are shifted, He is buffered to the inverting and non-inverting outputs by the emitter follower T4 And T5 transistor.


Here shown in figure that output register of emitter is Re4 And Re5.these both of are do not exist in the all the process of the ECL.


Sometimes 50 Ohm resistor is connected between bases.

HOw does emitter coupled logic work



Operation principle of emitter coupled logic (ECL)


Now lets talk about 
working principle of emitter coupled logic.


Emitter coupled logic is fastest switching logic among the all the switching logic family.


Its Also Known As current mode logic (CML)


Emitter coupled logic is also called CML because of the in ECL operation current switching is used.


Its has fixed biased emitter current.


which Approximate value is Ie=3mA


its path is from 1 collector terminal to another terminal of the transistor.


And its depend on the apply input logic level.


In the ECL circuit total two transistors.


Q1  And Other is Q2 for the differential Amplifier portion of the inverter circuit.in the base terminal of the Q2 transistor we apply the reference voltage  +Vref And At the base terminal of the transistor Q2 we apply input Logic level voltage.


Here Vi=-1.7 v  which is indicated that the Logic 0 at the input terminal or the base terminal of the transistor.

Ie is flow through the Collector terminal of the transistor Q2 For the logic 0.


Now we apply the Logic 1 at the input terminal then the Ie is flow through the collector terminal of the transistor Q1.Its flowing path is depend on the the input logic level.
 





Power Supplies Logic for the emitter coupled logic


Normally emitter coupled logic will operate on the negative power supplies and its positive of the supply is connected to the ground.

this is used to mainly minimize the influence in the power supply variations on the logic levels we know that the ECL is more sensitive to the noise.

Due to the ground is the most stable voltage system so ECL is operated on the positive ground system.

And in Case power supply variation voltage drop across collector resistors change slightly.





Features of the Emitter coupled logic(ECL)
(Advantage of emitter coupled logic)


Its name is emitter coupled logic because of the emitter of the BJT's are connected together.


transistors never saturated.transistor are prevented from going saturation by choosing the logic levels close to one another.storage delay in ECL circuit is eliminated.


the logic levels are normally -0.8v (logic 1) and -1.70v (logic 0)


Here propagation delay is minimum so speed is high.it has the fastest switching speed among the all other logic families.its propagation delay is around 1ns.


Due to low output impedance, fan out is large,fan out of ECL is around 25.You show that in the output side emitter follower circuit.
this emitter follower circuit is provided low output impedance,like value is 5 to 10 Ohm.


Fan out is around 25 that means our ECL logic circuit can try total 25 similar logic gates.


ECL logic circuit produces an output and its complement.this is eliminates the need of the inverters.


In case of ECL logic circuit we have 2 output terminal one is normal output and other is its complement so in the ECL logic circuit we don't need any inverter for the complement of the output.


current through Re is more or less constant.so no noise spikes will be generated like those produced by TTL totem-pole circuits.



 Disadvantages of emitter coupled logic(ECL)


  • Having logic levels close to each other , it has low noise margin around 0.25 v.so ECL circuits are not suitable for heavy industrial environment.


in ECL logic level Apply -0.8v  for the logic 1 and -1.7v for the logic 0.So different between two logic is only 0.8v so ECL circuits are get easily effected by the noise.


so instead of the ECL in large industrial circuit HCL (high threshold logic circuit) is used.which is give better immunity.

  • It requires relatively large silicon area and high cost.


In the ECL circuits has several BJT's and register.for this register required large silicon and due to large amount silicon its cost is became too high.

  • High power dissipation, Pd= 40mw

  • Due to high current, there is a problem to dissipates heat due to I^2R drops.


here Ie = 3mA and used some register in range of the 300 Ohm to 1K ohm so we get the several I^2 R drop in the circuit.this is the critical problem in the ECL circuit.

  • the ECL input and output are not electrically compatible for direct connection with any other logic family due to negative supply voltage and logic levels.





Advantage of emitter coupled logic over the CMOS


If we talk about speed of emitter coupled logic then it is higher then the previous RTL and DTL.

Smaller package compare to the RTL and DTL.

In emitter coupled logic circuit its output is depend on the current and last input(memory).

Emitter coupled logic is used for the fastest logic family work.

We talk about life then emitter coupled logic life is long , long obsolete.

Only one major disadvantage is its has very high power consumption.



Need Free PDF of emitter coupled logic ?

After read this fully detail guide on emitter coupled logic i am sure you say that please give us some of best material in pdf  form.

then don't worry i have some of best PDF which is not write by me , but i also refer for write this awesome post.

if you need then get from below link .click below for get emitter coupled logic pdf material.





Why emitter coupled family works on negative supply voltages? 






Normally emitter coupled logic circuit are work on the both positive and Negative supply.Main reason for the use of the Negative supply is the due to convention and ease of use in early day of the emitter coupled logic.


In the ECL circuit if the output is high voltage then written as Vcc-Vbe.And if output is low voltage then written as Vcc-Vbe-Vgate.

Vbe = base emitter voltage

Vbate = voltage swing of ECL gate

Its voltage level is change with the Vcc change.but buse as Vcc as the reference and use ground.So here Vee is became negative supply.

Vcc is drop out in all the levels because of the Vcc is ground and define as the its zero volt.

In the other convection process we also take Vcc is as positive and Vee is as ground.this connection is also called as PECL.



Click Here



For get more detail please refer below video lecture..






Final Words :



i Hope you like this detail guide about the Emitter coupled logic - ECL family. if you have any information regarding to the emitter coupled device then don't hesitate to share with us.we update this article with best of information for our readers.

Once again thanks for the read this post.stay updated and visit again for more updates.

[Detail Guide ] Basic of electronic switching devices

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Electronics switching devices 


electronics switching devices


Today here we talk about the different electronics switching devices.You All know that control any electrical process or any other process we need some of the switching systems.

Here we talk electronics switches which is Solid state and easily control the electrical power.

It is also used in the electronics and electrical engineering which deals with the design, control, computation and integration of nonlinear, time-varying energy-processing electronic systems with fast dynamics.

Many time ago in Electronics device mercury arc valves are used. but today modern time in the electronics switch some of the Diodes , transistor, thyristors are used.

Mostly these type of switch used in the AC/DC converter (rectifier).most of all the these device are used in the electricity transmission and its control process.




You show that in above figure here in electronics curcuit diagram many of Diodes , Capacitor , Inductor , Resistor and other small element is used.

 Now If you ask where the used these type of electronics switches..then ans is not limited for criteria of the application.

Electronics switches are unsed in the consumer electronic devices, e.g. television sets, personal computersbattery chargers, etc.  these are all is commercial but many industrial and other application is also used..


IF you say that which type of switches is used in regular general perpose...then this all name is below..




  • electronic vibration switch
  • electronic level switch
  • electric switchgear
  • electronic switchboard
  • electronic switch
  • electronic float switch
  • electronic pressure switch
  • electronic dimmer switch
  • electronic light switch
  • electronic switching system
  • electronic ignition switch
  • electronic switching devices

Now if we talk about its power range then it is from ten to several hundred of watt.

In industrial drive application we all are know that the electrical motor speed is control by the both method one is use of the mechanical switch and other is used of the electronics swiches.

Simply every people say that what switching action is better for the control action.electronics is far better then that of the mechanical.

in electronics no need of the any mechanical body and also its frictionless process.


Here We talk about the some of the best electronics devices and its some basic informattion


Basic electronics devices


1.Diode 

Description : Diode is one switching device.it has some characteristics like Uni-polar, uncontrolled, switching device used in applications such as rectification and circuit directional current control.it is reverse voltage blocking devices.

Ratings : It is a single silicon devices up to 3000 A and 5000 V.



2.Silicon controlled rectifier (SCR)

Description : this is the semiconductor switching devices.which is turn on when the gate pulse is apply.anode is positive with respect to the cathode terminal.Devices is became turn off when the its Anode is became Negative.

Ratings : It is single silicon device up to the 3000 A And 5000 v 



3.Thyristor

Description : Thyristor is the three terminal devices, in Thyristor include SCRs, GTOs, and MCT.these type of devices mostly gate pulse is responsible for the turn off and turn on condition.When these device is turn off then considered as the reverse voltage blocking devices.


4.GATE Turn off thyristor(GTO)

Description : some of semiconductor switching devices is turn on and off with the apply gate pulse but some time its need more GATE voltage for its turn off process.this turn off voltage is negative from gate to source.For this operation snubber circuit is required for the Turn off process.


5.Triac

Description : Triac is the devices in which pair of the phase controlled thyristors connected in inverse - parallel on the chip.when voltage pulse is present its work as turn on .many similarity in the triac and SCR.both when turn on then device cannot turn off.


6.Bipolar junction transistor (BJT)

Description : BJT is not use for the high power .compare to MOSFET it has more resistive losses.BJT have large base current so it has more losses.it is also unipolar device, so do not block reverse voltage very well.Mostly BJT is not used in the power electronics switching because it has more resistive losses.

Ratings : its has max rating around 1500 V and high current ratings.



7.Power MOSFET

Description : main advantages of Power mosfet as compared to BJT is almost zero gate current.MOSFET is the depletion layer devices.its GATE terminal not contribute any to either drain or source current.Its losses mostly attributed to the registers.its switching times s tens of the nanoseconds to some microseconds.if its losses are increased then its frequencies is also increase.MOSFET device is not Bidirectional devices also they are not reverse voltage blocking.



8.Insulated GATE Bipolar transistors (IGBT)

Description : these devices is has best characteristics then the MOSFET and BJT.its has mutual characteristics of both MOSFET and BJT.It has high GATE impedance like MOSFET devices.it has low GATE current like BJT.it has low power loss of switching action like BJT.

 Ratings : it excess for the 1500 A and switching voltage is up to 3000 V



9.MOS controlled thyristor (MCT)

Description : It is thyristor devices which can became turn ON & OFF by the MOSFET GATE pulse.here use MOS technology in which very little current is flow and very low control power signals is used.In this devices two MOSFET input and Pair of BJT is used in the output stage.Input side of the MOSFET is allow to use in control action during the positive and negative cycles.BJT is used for the Bidirectional control action.



10.integrated  gate commutated thyristor (IGCT)

Description : IGCT is similar devices like GTO.if you need quick switching action then the IGCT is the best.its output resistance is quite low and Don't waste of the power.


Ratings : it is work up to the 5000 V and 5000 A




Detail guide of fastest electronics switching device mosfet

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MOSFET As Switching devices ( MOSFET  tutorial )



fastest electronics switching device mosfet





Basic of the electronics switching device mosfet


what does mosfet mean ?

mosfet definition


let's started ,

Hi guys here we talk about the Detail guide of fastest electronics switching device mosfet.


You all are know that the MOSFET is the fastest switching devices.


Simply we called MOSFET in electronics Language then it is the metal oxide semiconductor field effect transistor.


It has Some of the ability to the change conductivity by the amount of the applied voltage.


Mosfet is the four terminal devices.they are like Source(S) , Gate(G) , Drain (D) and Body (B) terminals.


If you check in the electrical circuit then only appears three terminals.


If you say that how the Mosfet is different from the other switching devices then Mosfet has required very less amount of the current for the turn on.(less than 1mA).


Now we talk about the enhancement mode then in this mode voltage drop across the oxide induces a conducting channel  between the source and drain.


In the market different type of the Mosfet is available just like n channel mosfet , mosfet transistor , q point mosfet  , mosfet diode , radioshack mosfet , current mirror mosfet , aws raptor mosfet , fairchild mosfet , renesas mosfet , vgs mosfet , super junction mosfet , miller effect mosfet , high voltage mosfet , mosfet relay , mosfet switch , high current mosfet ,onsemi mosfet , k3569 mosfet , irf mosfet , quad mosfet , gan mosfet , gate mosfet , p channel mosfet switch , n channel mosfet basics , st mosfet etc..


Insulated gate field effect transistor or IGFET is the related term with the MOSFET.



Composite Material


mosfet switch design
fastest electronics switching device mosfet



Now We Talk about the MOSFET composite material then  MOSFET is the Chemical composition of the silicon and germanium.


If you say why sillicon if we think then find many semiconductors with better electrical properties than silicon, like gallium arsenide but it has not form good semiconductor-to-insulator interfaces.


Gate is separated by the thin insulating material of silicon dioxide and later of silicon oxynitride.


Now most of the companies have started to introduce a high-κ dielectric + metal gate combination.

  


Symbol of MOSFET 


Two type of MOSFET device is available 


1) N channel MOSFET 

2) P Channel MOSFET


We talk about these both topic in detail ....



fastest electronics switching device mosfet





Working of MOSFET (MOSFET operation)

how does a mosfet work


fastest electronics switching device mosfet


Mosfet is very small integrated circuit device.Large scale integration is impossible without the MOSFET switching device.


You know that MOSFET has Four terminal device.They are like Gate ,Drain. Source , Base etc..


Its Drain And source terminal are connected to the heavily doped region..Its Gate terminal is connected to the top of the oxide layer and its Body terminal is connected to the intrinsic semiconductor.


In between the Drain and Source terminal inversion layer is create so current flow in this inversion layer is controlled by Gate voltage.Thus MOSFET is voltage controlled device.


Generally Two type of MOSFET device is available N channel And P channel MOSFET.


In N channel MOSFET Current is flow due to the electrons in inversion layer And in P channel layer current is flow due to the holes.


Another Charecteristics is like enhancement type and depletion type MOSFETs. 


In the Enhancement mode Turn off and On by apply the GATE voltage.opposition process is happen in the depletion type of MOSFET.



Working Principle of MOSFET



Working principle of MOSFET is depend on the MOS capacitor.main important part of the MOSFET is MOS capacitor.


Here apply Positive and Negative gate voltages respectively for the surface below the oxide layer and between the  drain and source terminal can converted in to the P-type and N-type.


When We apply the positive Gate voltage then the oxide layer experience the repulsive force and holes are the pushes downward.


Its depletion region is bounded by the negative changes.which is associated with acceptor atoms. 


Also the Positive voltage is attracts to the electron from the  N+ source and drain .


Now if we apply the voltage between the source and the drain  then the current is flow freely between the source and drain.


If we apply the negative voltage then the hole channel will be formed beneath the oxide layer. 


For the conduction of the current between source and drain  we need to controlling of the source to gate voltage.


When gate voltage is exceed to given level then conduction is started,


shown in below equation for the more detail guide..



  Here ,

UN = Mobility of electron
COX  = Capacitance of the oxide layer
W = Width of the gate area
L = Length of the channel
VGS = Gate to Source voltage
VTH  = Threshold voltage
VDS  = Drain to Source voltage.


For get some basic principle of MOSFET check below video tutorial








Two type of MOSFET device is available 



1) P channel MOSFET 



2) N Channel MOSFET






1) P channel MOSFET 



If P channel region in between Source and Gate then called is P channel MOSFET.P - MOSFET is four terminal device.they are like Gate , drain , Source and Body.

In this Four terminal Drain and source are heavily doped P+ region.Body region is the N type region.

In the p channel material current is flow due to the Positive Holes that's why that material is also called as the P type material.

P type material is composite of the P+ donor material.

Now if we apply negative supply then electron is present in the oxide layer which experience a repulsive force and electron are pushed in downward in to the body region.

and here depletion region is populated by the positive atoms which is due to the donor atoms.

Due to this negative voltage apply is also attracts the holes from the P+ source and drain material.

Now due to this apply voltage between source and drain current is flow.

It has two mode of operation 

1) enhancement Mode

2) depletion Mode

For this shown in below diagram for detail information












2) N Channel MOSFET



Mosfet material which having the N-type of region in between source and drain is known as the N- channel MOSFET.

N-MOSFET is four terminal device.they are like Gate , drain , Source and Body.

Here some of is exact opposite from the P channel MOSFET.

Here Drain and Source region is heavily Doped N+ region.

Body is the P Type of doping.Here current is flow due to the Negatively charge electrons,and that's why this type of MOSFET is called as the N-type MOSFET.

Here when we apply the Positive gate voltage then the Holes is also present in the oxide layer so repulsive force are create.

So holes are pushes in to the downwards.

Gue to This positive gate voltage Also attracts the electrons from the  N+ source and drain.so electrons reach channel is formed.

Now we apply voltage between Gate and source terminal of the MOSFET.

Here in the N type of MOSFET Electron concentration is prefered over the P type of material.

In N type of material Mobility of Electrons is much higher then the Mobility of holes in the P type of the MOSFET.

It has two mode of operation 

1) enhancement Mode

2) depletion Mode

For this shown in below diagram for detail information







free Download emitter coupled logic pdf

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emitter coupled logic pdf




 free Download emitter coupled logic pdf



Free download best emitter coupled logic Pdf



Hi hello , friends welcome to my blog.you are here that means you are interested to the get the pdf Of emitter coupled logic.if you need detail operation about the emitter coupled logic then click here.

you know that the emitter coupled logic is the fastest switching device.it is integrated circuit which is part of bipolar transistor logic family.

We talk about the family member of the logic family then which are like RTL , DTL ,ECL , TTL , IIL ,CMOS , BICMOS , PMOS , NMOS , MOSFET , HMOS etc.

ECL is Also Sometimes know that the current mode logic.its basic structures are similar to differential amplifier configuration.

Here circuit is operate on the negative Power supply and grounded.

You are all know that we talk about all the detain configuration in the our main post.

So here we now talk that some of the characteristics of the Emitter coupled logic circuits.


characteristics of the emitter coupled logic


Now we talk about the characteristics of the emitter coupled logic then it has large current requirement is approximately constant.

ECL is not depend significantly on the state of the circuit.

ECL circuits generate relatively little power noise.power noise sometimes became problematic.

Propagation time is very less which is in nano second.so ECl is the fastest element in the logic family.

If we talk about fastest multi cheap processor then ECL is one of them.



Best PDF material of emitter coupled logic download from below link..



For download PDf of the Emitter coupled logic from the Department of Electrical Engineering Indian Institute of Technology, Madras then click here..



For download pdf from the Department of Physics, Indian Institute of Technology Guwahati, India  then  click here...


Foe download pdf from the Oxford University Press click here ..






Final words :


I hope this post  free Download emitter coupled logic pdf is helpful for you for get the pdf of the Basic of ECL.

If you have any suggestion or any other useful information then please contact us and we are always ready for the accept knowledge from our audience.

thanks for the read the this awesome post..


Emitter coupled logic - ECL family

· 3 comments

emitter coupled logic


emitter coupled logic



emitter coupled logic definition



Hi Hello Guys , You are here that means you are so exciting about know the principle of the Emitter coupled logic.

Here we represented some of the all the basic funda and detail information about the emitter coupled logic - ECL family.

So Without wasting of your time i am starting the full detailed article about the Emitter coupled logic.

What is electronics switching devices ?


It is also used in the electronics and electrical engineering which deals with the design, control, computation and integration of nonlinear, time-varying energy-processing electronic systems with fast dynamics.


Many time ago in Electronics device mercury arc valves are used. but today modern time in the electronics switch some of the Diodes , transistor, thyristors are used.


Mostly these type of switch used in the AC/DC converter (rectifier).most of all the these device are used in the electricity transmission and its control process.




For more detail guide of Basic of electronic switching devices



Which is Fastest electronics device ?



You all are know that the MOSFET is the fastest switching devices.


Simply we called MOSFET in electronics Language then it is the metal oxide semiconductor field effect transistor.


It has Some of the ability to the change conductivity by the amount of the applied voltage.


Mosfet is the four terminal devices.they are like Source(S) , Gate(G) , Drain (D) and Body (B) terminals.


If you check in the electrical circuit then only appears three terminals.

For more detail guide on fastest electronics switching device mosfet



Basic Of  Emitter coupled logic(ECL)



In electronics family Emitter coupled logic (ECL) is the high speed integrated circuit bipolar transistor.

ECL is used as overdriven BJT differential Amplifier.It has single ended input and Limited emitter current to avoid from the saturated region of the operation.

And its has slow turn off behavior.

Here current is flow in two legs of emitter coupled pair.ECL is also sometimes called as the current steering logic (CSL) , Current mode logic (CML) , current switch emitter follower (CSEF) logic.

We already talk that Transistors are never in saturation region , its input and output voltages have very small swing like 0.8.

We all know that its input impedance is high and its output impedance is low.

You know that transistor is switching device and transistor is quickly change its state.


Its Fanout capabilities is high.it is essentially constant current draw of the differential amplifiers.


It is the decrease the propagation  time of the whole circuit by reducing inverter count.


If you ask about different electronics switching devices like Mosfet , IGBT , Transistor , GTO , Diac , Triac etc..

IF you curious to know about the MOSFET as the Fastest switching devices then go for .....


History of emitter coupled logic(ECL)



Emitter coupled logic was invented in August 1956 at IBM by Hannon s.Yourke.Its also called as current-steering logic.Its logic also called as current mode circuit.

It is also used in the make ASLT circuit in IBM.

In this differential amplifiers Whose input logic levels were different from the output logic levels.

In the beginning of the  1960 ECL circuit were implemented on monolithic integrated circuits.

First Monolithic circuits is Introduced by the Motorola in 1962. Also Motorola developed several improved series in 1966.

Which has 1 nanosecond gate propagation time and which has 300 MHZ flip-flop  toggle rates.

The ECLinPS family is introduced in the 1987.

Now we talk about the GATE delay then 500 ps single gate delay and it has 1.1 GHZ flip-flop toggle frequency.

ECl has High power Consumption So its used is mainly for the High speed requirement.





Basic Circuit Diagram of emitter coupled logic(ECL)


emitter coupled logic tutorial


positive emitter coupled logic


image credit wikipedia  

                                                           emitter coupled logic circuit




ECL is devised which is based on the emitter coupled pair.For The Detail Shown in the above figure.


Shown in figure that left half of the pair which has two parallel-connected input transistors T1 and T2.And Input NOR Logic is used.


Shown on figure that on the right T1 And T2 Transistor T3 is provided which based voltage is fixed by a reference voltage source.


In shaded light green voltage divider with diode thermal compensation (R1,R2 and D1,D2) And also buffering emitter follower.


Emitter voltage is kept relatively steady.Re is the common emitter resistance which work like current source.


output voltage of the collector load here resistors Rc1 and Rc3 are shifted, He is buffered to the inverting and non-inverting outputs by the emitter follower T4 And T5 transistor.


Here shown in figure that output register of emitter is Re4 And Re5.these both of are do not exist in the all the process of the ECL.


Sometimes 50 Ohm resistor is connected between bases.

HOw does emitter coupled logic work



Operation principle of emitter coupled logic (ECL)


Now lets talk about 
working principle of emitter coupled logic.


Emitter coupled logic is fastest switching logic among the all the switching logic family.


Its Also Known As current mode logic (CML)


Emitter coupled logic is also called CML because of the in ECL operation current switching is used.


Its has fixed biased emitter current.


which Approximate value is Ie=3mA


its path is from 1 collector terminal to another terminal of the transistor.


And its depend on the apply input logic level.


In the ECL circuit total two transistors.


Q1  And Other is Q2 for the differential Amplifier portion of the inverter circuit.in the base terminal of the Q2 transistor we apply the reference voltage  +Vref And At the base terminal of the transistor Q2 we apply input Logic level voltage.


Here Vi=-1.7 v  which is indicated that the Logic 0 at the input terminal or the base terminal of the transistor.

Ie is flow through the Collector terminal of the transistor Q2 For the logic 0.


Now we apply the Logic 1 at the input terminal then the Ie is flow through the collector terminal of the transistor Q1.Its flowing path is depend on the the input logic level.
 





Power Supplies Logic for the emitter coupled logic


Normally emitter coupled logic will operate on the negative power supplies and its positive of the supply is connected to the ground.

this is used to mainly minimize the influence in the power supply variations on the logic levels we know that the ECL is more sensitive to the noise.

Due to the ground is the most stable voltage system so ECL is operated on the positive ground system.

And in Case power supply variation voltage drop across collector resistors change slightly.





Features of the Emitter coupled logic(ECL)
(Advantage of emitter coupled logic)


Its name is emitter coupled logic because of the emitter of the BJT's are connected together.


transistors never saturated.transistor are prevented from going saturation by choosing the logic levels close to one another.storage delay in ECL circuit is eliminated.


the logic levels are normally -0.8v (logic 1) and -1.70v (logic 0)


Here propagation delay is minimum so speed is high.it has the fastest switching speed among the all other logic families.its propagation delay is around 1ns.


Due to low output impedance, fan out is large,fan out of ECL is around 25.You show that in the output side emitter follower circuit.
this emitter follower circuit is provided low output impedance,like value is 5 to 10 Ohm.


Fan out is around 25 that means our ECL logic circuit can try total 25 similar logic gates.


ECL logic circuit produces an output and its complement.this is eliminates the need of the inverters.


In case of ECL logic circuit we have 2 output terminal one is normal output and other is its complement so in the ECL logic circuit we don't need any inverter for the complement of the output.


current through Re is more or less constant.so no noise spikes will be generated like those produced by TTL totem-pole circuits.



 Disadvantages of emitter coupled logic(ECL)


  • Having logic levels close to each other , it has low noise margin around 0.25 v.so ECL circuits are not suitable for heavy industrial environment.


in ECL logic level Apply -0.8v  for the logic 1 and -1.7v for the logic 0.So different between two logic is only 0.8v so ECL circuits are get easily effected by the noise.


so instead of the ECL in large industrial circuit HCL (high threshold logic circuit) is used.which is give better immunity.

  • It requires relatively large silicon area and high cost.


In the ECL circuits has several BJT's and register.for this register required large silicon and due to large amount silicon its cost is became too high.

  • High power dissipation, Pd= 40mw

  • Due to high current, there is a problem to dissipates heat due to I^2R drops.


here Ie = 3mA and used some register in range of the 300 Ohm to 1K ohm so we get the several I^2 R drop in the circuit.this is the critical problem in the ECL circuit.

  • the ECL input and output are not electrically compatible for direct connection with any other logic family due to negative supply voltage and logic levels.





Advantage of emitter coupled logic over the CMOS


If we talk about speed of emitter coupled logic then it is higher then the previous RTL and DTL.

Smaller package compare to the RTL and DTL.

In emitter coupled logic circuit its output is depend on the current and last input(memory).

Emitter coupled logic is used for the fastest logic family work.

We talk about life then emitter coupled logic life is long , long obsolete.

Only one major disadvantage is its has very high power consumption.



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Why emitter coupled family works on negative supply voltages? 






Normally emitter coupled logic circuit are work on the both positive and Negative supply.Main reason for the use of the Negative supply is the due to convention and ease of use in early day of the emitter coupled logic.

In the ECL circuit if the output is high voltage then written as Vcc-Vbe.And if output is low voltage then written as Vcc-Vbe-Vgate.

Vbe = base emitter voltage

Vbate = voltage swing of ECL gate

Its voltage level is change with the Vcc change.but buse as Vcc as the reference and use ground.So here Vee is became negative supply.

Vcc is drop out in all the levels because of the Vcc is ground and define as the its zero volt.

In the other convection process we also take Vcc is as positive and Vee is as ground.this connection is also called as PECL.



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