BICMOS INVERTERS.pptx

8/14/2019 BICMOS INVERTERS.pptx

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By

Syed Inthiyaz

BiCMOS INVERTERS


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The simplified BiCMOS Inverter

Two bipolar transistors (T3

and T4), one nMOS and

one pMOS transistor (both

enhancement-type

devices)

Vin = 0 :

T1 is off. Therefore T3 is non-

conducting

T2 ON - supplies current tobase of T4

T4 base voltage set to Vdd.

T4 conducts & acts as current

source to charge load CL towards

Vdd.

Vout rises to Vdd - Vbe (of T4)


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The simplified BiCMOS

Inverter(Contd..)

Vin = Vdd :

T2 is off.Therefore T4 is non-

conducting.

T1 is on and supplies current to the

base of T3

T3 conducts & acts as a current

sink to discharge load CL towards 0V. Vout falls to 0V+ VCEsat (of T3)

T3 & T4 present low impedances when turned on

into saturation & load CL will be charged or

discharged rapidly


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Advantages

Output logic levels will be good & will beclose to rail voltages since VCEsat is

quite small & VBE 0.7V. Therefore,

inverter has high noise margins

Inverter has high input impedance, i.e.,

MOS gate input

Inverter has low output impedance

Inverter has high drive capability butoccupies a relatively small area


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Disadvantages

However, this is not a good arrangement toimplement since no discharge path exists

for current from the base of either bipolar

transistor when it is being turned off, i.e.,

when Vin=Vdd

T2 is off and no conducting path to the base

of T4 exists when Vin=0

T1 is off and no conducting path to the baseof T3 exists

This will slow down the action of the circuit


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Alternative BiCMOS Inverter with no

static current flow

The DC path through

T3and T1 is eliminated

The output swing isnow reduced, since the

output cannot fall below

the base to emitter VBE

of T3


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BiCMOS Inverter using Resistors

In this circuit resistors

provide the improved

swing of output voltage

when each bipolartransistor is off,

It also provide

discharge paths for basecurrent during turn-off.

The provision of on chip resistors of

suitable value is not always convenient and

may be space-consuming, so that other


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BiCMOS Inverter using MOS

transistors for base current discharge

Vin = 0 : T,1T3,T6 are off

T2,T4,T5 are ON

T4 base voltage set to Vdd.

T4 conducts & acts as curren

source to charge load CL

towards Vdd.

Vout rises to Vdd


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transistors for base current discharge

(Contd..)

Vin = Vdd :

T2,T4,T5 are Off

T,1T3,T6 are oN

The load CL dischargethrough T1 and T6 towards 0v.


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Documents

BICMOS INVERTERS.pptx