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Pass Transistor Logic
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
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
nMOS Pass Transistor – Logic ‘1’ Transfer
nMOS Pass Transistor – Logic ‘0’ Transfer
PASS TRANSISTORS IN SERIES
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
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.
TRANSMISSION GATE
PROBLEMS WITH TRANSMISSION GATES
No isolation between the input and output. Output progressively deteriorates as it passes through
various stages.
However designs get simplified.
TRANSMISSION GATE - LAYOUT
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
Multiplexor
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
XOR gate
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
D – Latch
TIMING ISSUES
D LATCH
D - LATCH
D LATCH – ALTERNATE CIRCUIT TOPOLOGY
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
Static Flip Flop
0
1
D1
0
Q
ClkClk
Transparent when Clk=0
Transparent when Clk=1
At Clk= 0 1, Q = D. Else Q is held.
D Flip Flop – Circuit Diagram
D Flip Flop - Operation
D Flip Flop - Waveforms
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
Handling Clock Skew
Clk-in Clk
Clk'
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
Pass Transistor Logic Families
Complementary Pass Transistor Logic Family Dual Pass Transistor Logic Family Swing Restored Pass Transistor Logic Family
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.
Solution - 1
C'0
C0
C1
C'1
Y
A0
A1
A2
A3
Solution - 2
C'0
C0 C'1
A0
A1
A2
A3
C1 Y
XOR Gate
A B
AB
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