The document discusses pass transistor logic circuits. It describes how nMOS pass transistors can transfer logic 1 and 0 signals. Transmission gates are introduced which use both nMOS and pMOS pass transistors to pass strong signals in both directions. Applications of transmission gates include multiplexers, XOR gates, D latches, and D flip-flops. Clock skew management and different pass transistor logic families are also covered.

1. Pass Transistor
Logic

2. Agenda









Introduction
VLSI Design methodologies
Review of MOS Transistor Theory
Inverter – Nucleus of Digital Integrated Electronics
Static CMOS Logic Circuits
Pseudo nMOS Logic Circuits
Pass Transistor Logic Circuits
Dynamic Logic Circuits
Case Studies

3. Pass Transistor Logic
Circuits
 nMOS
Pass transistor – transmission
properties
 Transmission Gates
 Transmission Gate Applications
 Mux
 XOR
 D Latch
 D Flip Flop
 Clock Skew management
 Pass Transistor Logic Families

4. nMOS Pass Transistor – Logic ‘1’
Transfer

5. nMOS Pass Transistor – Logic
‘0’ Transfer

7. PASS TRANSISTORS IN
SERIES

8. PASS TRANSISTOR LOGIC
CIRCUITS
 nMOS
Pass transistor – transmission properties
 Transmission Gates
 Transmission Gate Applications
 Mux
 XOR
 D Latch
 D Flip Flop
 Clock Skew management
 Pass Transistor Logic Families

9. TRANSMISSION GATES
 NMOS
pass transistor passes a strong 0 and a weak 1.
 PMOS pass transistor passes a strong 1 and a weak 0.
 Combine the two to make a CMOS pass gate which will
pass a strong 0 and a strong 1.

10. TRANSMISSION GATE

11. PROBLEMS WITH
TRANSMISSION GATES
 No
isolation between the input and output.
 Output progressively deteriorates as it passes through
various stages.
However designs get simplified.

12. TRANSMISSION GATE - LAYOUT

13. PASS TRANSISTOR LOGIC
CIRCUITS
 nMOS
Pass transistor – transmission properties
 Transmission Gates
 Transmission Gate Applications
 Mux
 XOR
 D Latch
 D Flip Flop
 Clock Skew management
 Pass Transistor Logic Families

14. Multiplexor

15. Pass Transistor Logic Circuits
 nMOS
Pass transistor – transmission properties
 Transmission Gates
 Transmission Gate Applications
 Mux
 XOR
 D Latch
 D Flip Flop
 Clock Skew management
 Pass Transistor Logic Families

16. XOR gate

17. PASS TRANSISTOR LOGIC
CIRCUITS
 nMOS
Pass transistor – transmission properties
 Transmission Gates
 Transmission Gate Applications
 Mux
 XOR
 D Latch
 D Flip Flop
 Clock Skew management
 Pass Transistor Logic Families

18. D – Latch

19. TIMING ISSUES

20. D LATCH

21. D - LATCH

22. D LATCH – ALTERNATE CIRCUIT
TOPOLOGY

23. PASS TRANSISTOR LOGIC
CIRCUITS
 nMOS
Pass transistor – transmission properties
 Transmission Gates
 Transmission Gate Applications
 Mux
 XOR
 D Latch
 D Flip Flop
 Clock Skew management
 Pass Transistor Logic Families

24. Static Flip Flop
Clk
D
Clk
0
1
1
0
Transparent when
Clk=0
Q
Transparent when
Clk=1
At Clk= 0 → 1, Q = D. Else Q is held.

25. D Flip Flop – Circuit
Diagram

26. D Flip Flop - Operation

27. D Flip Flop - Waveforms

28. Pass Transistor Logic Circuits
 nMOS
Pass transistor – transmission properties
 Transmission Gates
 Transmission Gate Applications
 Mux
 XOR
 D Latch
 D Flip Flop
 Clock Skew management
 Pass Transistor Logic Families

29. Handling Clock Skew
Clkin
Clk
Clk'

30. Pass Transistor Logic Circuits
 nMOS
Pass transistor – transmission properties
 Transmission Gates
 Transmission Gate Applications
 Mux
 XOR
 D Latch
 D Flip Flop
 Clock Skew management
 Pass Transistor Logic Families

31. Pass Transistor Logic
Families



Complementary Pass Transistor Logic Family
Dual Pass Transistor Logic Family
Swing Restored Pass Transistor Logic Family

32. Problems
 Design
4 to 1 multiplexor using transmission-gates.
 Implement an XOR gate using minimum number of
transistors.
 Implement a full adder using transmission gates.

33. Solution - 1
C1
C'0
A0
C0
A1
A2
A3
C'1
Y

34. Solution - 2
C'0
A0
C0
A1
A2
A3
C'1
C1
Y

35. XOR Gate
A
B
A⊕B