4:1 Multiplexer using Transmission gate logic & Pass transistor logic

4:1 Multiplexer using Transmission Gate logic-

Truth table and circuit diagram-

Operation-
When S0=0, S0=0 then TG1 & TG2 transistor will be ON and current I0 will be transmitted to output through TG1 & TG2.
When S1=0, S0=1 then TG3 & TG4 transistor will be ON and current I1 will be transmitted to output through TG3 & TG4.
When S1=1, S0=0 then TG5 & TG6 transistor will be ON and current I2 will be transmitted to output through TG5 & TG6.
When S1=1, S0=1 then TG7 & TG8 transistor will be ON and current I3 will be transmitted to output through TG7 & TG8.

4:1 multiplexer using minimum Transmission Gates(6 Transmission gates) -
Truth table and circuit diagram-

Operation-
When S1=0, S0=0 then TG1 & TG3 transistor will be ON and current I0 will be transmitted to output through TG1 & TG3.
When S1=0, S0=1 then TG2 & TG3 transistor will be ON and current I1 will be transmitted to output through TG2 & TG3.
When S1=1, S0=0 then TG4 & TG6 transistor will be ON and current I2 will be transmitted to output through TG4 & TG6.
When S1=1, S0=1 then TG5 & TG6 transistor will be ON and current I3 will be transmitted to output through TG5 & TG6.

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4:1 Multiplexer using Pass transistor logic-

Truth table and circuit diagram-

Operation-
When S1=0, S0=0 then M1 & M2 transistor will be ON and current I0 will be transmitted to output through M1 & M2.
When S1=0, S0=1 then M3 & M4 transistor will be ON and current I1 will be transmitted to output through M3 & M4.
When S1=1, S0=0 then M5 & M6 transistor will be ON and current I2 will be transmitted to output through M5 & M6.
When S1=1, S0=1 then M7 & M8 transistor will be ON and current I3 will be transmitted to output through M7 & M8.

4:1 multiplexer using minimum Pass Transistor(6 pass transistor) -
Circuit diagram-

Technology Topper Thursday, March 19, 2020

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Pass Transistor Logic - realization of NAND, NOR, AND, OR Gates using pass transistor

Pass Transistor Logic-realization of NAND, NOR, AND, OR Gates using pass transistor

Pass transistor logic-

• Pass transistor logic can be used to implement complex logic circuits. Pass transistor logic utilizes n-MOS transistors only.
• In pass transistor logic the primary inputs drive the gate terminals and source-drain terminal unlike static CMOS logic where primary inputs drive the gate terminal.
• If input to the gate of the transistor is one then transistor will be on and current will flow through the transistor, and if input to he gate of the transistor is zero then transistor will be off and current will not flow through the transistor.

>>2 input NAND Gate using pass transistor-

According to the relation of B & Output column of truth table 1 & Bbar applied to the input side. 

When A=0, B=0 then transistor M1 is ON and M2 is OFF then output become 1 and node capacitance will charge through M1. 

When A=0, B=1 then transistor M1 is ON and M2 is OFF then output become 1 and node capacitance will charge through M1. 

When A=1, B=0 then transistor M1 is OFF and M2 is ON then output become 1 and node capacitance will charge through M2. 

When A=1, B=1 then transistor M1 is OFF and M2 is ON then output become 0 and node capacitance will discharge through M2.

>>2 input NOR Gate using pass transistor-

According to the relation of B & Output column of truth table Bbar & 0 applied to the input side. 

When A=0, B=0 then transistor M1 is ON and M2 is OFF then output become 1 and node capacitance will charge through M1. 

When A=0, B=1 then transistor M1 is ON and M2 is OFF then output become 0 and node capacitance will discharge through M1. 

When A=1, B=0 then transistor M1 is OFF and M2 is ON then output become 0 and node capacitance will discharge through M2. 

When A=1, B=1 then transistor M1 is OFF and M2 is ON then output become 0 and node capacitance will discharge through M2.

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>>2 input AND Gate using pass transistor-

According to the relation of B & Output column of truth table 0 & B applied to the input side. 

When A=0, B=0 then transistor M1 is ON and M2 is OFF then output become 0 and node capacitance will discharge through M1. 

When A=0, B=1 then transistor M1 is ON and M2 is OFF then output become 0 and node capacitance will discharge through M1. 

When A=1, B=0 then transistor M1 is OFF and M2 is ON then output become 0 and node capacitance will discharge through M2. 

When A=1, B=1 then transistor M1 is OFF and M2 is ON then output become 1 and node capacitance will charge through M2. 

>>2 input OR Gate using pass transistor-

According to the relation of B & Output column of truth table B & 1 applied to the input side. 

When A=0, B=0 then transistor M1 is ON and M2 is OFF then output become 0 and node capacitance will discharge through M1. 

When A=0, B=1 then transistor M1 is ON and M2 is OFF then output become 1 and node capacitance will charge through M1. 

When A=1, B=0 then transistor M1 is OFF and M2 is ON then output become 1 and node capacitance will charge through M2. 

When A=1, B=1 then transistor M1 is OFF and M2 is ON then output become 1 and node capacitance will charge through M2.

Advantages of pass transistor logic-

• They are not ratioed devices and can be of minimum geometry. Hence area required is less.
• They don't have path from positive supply terminal to ground and don't dissipate standby power.
• Speed is more.

Disadvantages of pass transistor logic-

• High level output is weak. Due to this the high level noise margin is less.

Technology Topper Friday, March 13, 2020

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