Field-Effect Transistors 1.Understand MOSFET operation. 2. Understand the basic operation of CMOS logic gates. 3. Make use of p-fet and n-fet for logic gate implementation

NMOS AND PMOS TRANSISTORS

The MOS Transistor

Cross-Section of CMOS Technology

MOS transistors Types and Symbols D S G NMOS Enhancement G D S PMOSEnhancement

NMOS

Threshold Voltage: Concept

PMOS

Mode of Operation Cut off Liner Saturation

Operation in the Cutoff Region

Operation in the Linear Region

Operation in the Saturation

Transistor in Saturation

MOSFET Summary

CMOS Inverter

MOS transistors logic input D S G NMOS Enhancement G D S PMOSEnhancement G =‘1’ then turn on the n-fet as Vgs > V threshold G = ‘0’ then turn on the p-fet as Vgs is negative as Vs > Vg

CMOS NAND Gate

CMOS NOR Gate

The Ideal Gate

Delay Definitions

CMOS INVERTER

The CMOS Inverter: A First Glance

CMOS Properties Full rail-to-rail swing Symmetrical VTC Propagation delay function of load capacitance and resistance of transistors No static power dissipation Direct path current during switching

Voltage Transfer Characteristic

CMOS Inverter VTC

Simulated VTC

Where Does Power Go in CMOS?

Dynamic Power Dissipation Energy/transition = C L * V dd 2 Power = Energy/transition *f =C L * V dd 2 * f Need to reduce C L, V dd, andf to reduce power. VinVout C L Vdd Not a function of transistor sizes!

CMOS Logic Implementation A CMOS logic gate consists of p-tree for pull-up n-tree for pull-down.

CMOS Logic Implementation Duality f = A+B’C if A = ‘1’, or B=‘0’ and C=‘1’, then f = ‘1’ if the logic function is in the form as f, then use Direct Implementation, for the P-tree implementation and logic function  series connection so the term B`C is in series or logic function  parallel connection so A, B`C is in parallel use complement of the input signals That is, A`, B and C` are used as inputs

CMOS Logic Implementation f = A+B’C A = ‘1’  A`= ‘0’, P1 on B’= ‘1’  B = ‘0’ P2 on C = ‘1’  C`= ‘0’, P3 on either P1 on or P2 and P3 are on then f = ‘1’ Since ‘0’ is need to turn on the use A`, B and C` as the inputs to the P- tree, instead of the original input variables. Both p-tree and n-tree have the same set of inputs.

CMOS Gate Implementation Once P-tree is designed, use duality for the N- tree Duality Series connection in P – tree  parallel for N- tree Parallel connection in P-tree  series for N-tree f = A+B’C if A = ‘1’, A`=‘0’, B’=‘1, B=‘0’ and C=‘1’, C`=‘0’, then f = ‘1’ pull up the output through the p-tree net if A = ‘0’, A`=‘1’, B’=‘0’, B=‘1’ and C=‘0’, C`=‘1’, then f = ‘0’ pull down the output through n-tree net

CMOS Gate Implementation f = A+B’C A = ‘1’, A`=‘0’, P1 turn on or B’=‘1, B=‘0’, P2 turn on and C=‘1’, C`=‘0’, P3 turn on then f = ‘1’ pull up the output through the p-tree net through P1 or P2 and P3 if A = ‘0’, A`=‘1’, N1 turn on B’=‘0’, B=‘1’, N2 turn on or C=‘0’, C`=‘1’, N3 turn on then f = ‘0’ pull down the output through n-tree net through N1 and N2, or N1 and N3

CMOS Gate Implementation If f is in this form, there are two ways to implement the logic gate for the logic function. 1.expand the logic function through de Morgan rule and direct implementation on the expanded function. f = (A+B`C)` = A`(B`C)`= A`(B``+C`) = A`(B+C`) Implement the logic gate with the previous method, the input signals are A, B` and C

CMOS Gate Implementation Use duality to complete design for the n-tree

CMOS Gate Implementation 2. Take then, g = A+B`C Use g to define the n-tree configuration. If g is true  f = ‘0’ Same implementation rule apply, and logic function  series connection so the term B`C is in series or logic function  parallel connection, and input variables remain un-change A = ‘1’, g is true, N1 on B`= ‘1’, and C = ‘1’, g is true N2 and N3 are on

CMOS Gate Implementation Use the duality to complete design for the p-tree.

Comparison of Design Method f = (A+B`C)`, f =g`, g = A+B`C Use g to define the circuit configuration for the N-tree, and the input variables are those of the logic function, g; that is, A, B` and C By de Morgan rule on f, f = A`(B+C`), and use the expended form to define the circuit configuration for the P-tree, and the input variables are the complementary of the variables of the expended form. As f = A`(B+C`), the input variables are A`, B, and C`, the complementary of these signals are A, B` and C. Comparing the two approach, there is conflict between the two as the input variables are the same as A, B` and C. And the circuit configuration of P-tree and N-tree are in fact observe the de Morgan rule or duality.

CMOS Gate Implementation It has to remind that the p-tree has to be connected to Vdd for pull-up the output and the n-tree has to be connected to GND for pull-down the output. It cannot use n-tree for the pull-up and p-tree for the pull-down as the full-swing property will not be maintained. i. e. logic ‘0’ ≠ zero volt logic ‘1’ ≠ Vdd volts