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