Download Pass Transistor

Pass Transistor
Logic
EMT 251
Pass Transistor Logic
Inputs
B
Switch
Out
A
Out
Network
B
B
Pass Transistor Logic
Gate is static – a low-impedance path
exists to both supply rails under all
circumstances
 NMOS transistors only
 No static power consumption
 Ratioless (W/L)
 Bidirectional (versus undirectional)

Complementary Pass Transistor
Logic (CPL)
Dual-rail form of pass transistor logic
 Avoids need for ratioed feedback
 Optional cross-coupling for rail-to-rail
swing

Example: AND/NAND gate
Example: OR/NOR gate
Example : XOR/XNOR gate
Cascaded Technique
Wrong!!
Correct!!

Draw a CMOS circuit based on this logic
equation. Use a minimum number of
transistors.
Transmission Gate
Logic
EMT 251
Transmission Gate Logic (TG)
s
A(Vin )
P
s
B (Vout )
B (Vout )
A (Vin )
N
s




s
Most widely used solution
Use both NMOS and PMOS in parallel
Can be used for logic circuit implementation
Full swing bidirectional switch controlled by the
gate signal (strong ‘0’ and ‘1’)
The MOS transistor pass gate
nMOS
1
1
1
0 passes a good 0
pMOS
0
passes a bad 1
0
Near Short CCT
Resistance small
1
0
passes a bad 0
passes a good 1
TG as a Tristate Buffer
A
B=A
(or Z when S=0)
s
In steady state
A(Vin) S
0
0
0
1
1
0
1
1
Tn
off
on
off
off
Tp
off
off
off
on
B (Vout)
Z (high impedance state (blocks logic flow))
0 (nMOS passes strong 0, pMOS off when Vout<Vthp)
Z (high impedance state (blocks logic flow))
1 (pMOS passes strong 1, nMOS off when Vout>Vdd-Vthn )
Example : OR gate
Example : AND gate
Example : XOR gate