Transcript Chapter 10 Digital CMOS Logic Circuits

Chapter 10
Digital CMOS Logic Circuits
• 10.1 Digital circuit design : An overview
• 10.2 Design and performance analysis of the CMOS
inverter
• 10.3 CMOS logic gate circuits
• 10.4 Pseudo- NMOS logic circuits
10.1 Digital circuit Design : An Overview
10.1.1 Digital IC technologies and logic circuit families
Fig. 10.1 Digital IC technologies and logic circuit families
CMOS
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Replaced NMOS (much lower power dissipation)
Small size, ease of fabrication
Channel length has decreased significantly (as short as 0.06 µm or shorter)
Low power dissipation than bipolar logic circuits ( can pack more) .
High input impedance of MOS transistors can be used to storage charge
temporarily (not in bipolar)
High levels of integration for both logic (chapter 10) and memory circuits
(chapter 11) .
Dynamic logic to further reduce power dissipation and to increase speed
performance .
Bipolar
• TTL (Transistor-transistor logic) had been used for many
years .
• ECL (Emitter –Coupled Logic) : basic element is the
differential BJT pair in chapter 7 .
• BiCMOS : combines the high speed of BJT’s with low
power dissipation of CMOS .
• GaAs : for very high speed due to the high carrier
mobility . Has not demonstrated its potential
commercially .
Features to be Considered
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Interface circuits for different families
Logic flexibility
Speed
Complex functions
Noise immunity
Temperature
Power dissipation
Co$t
10.1.2 Logic circuit characterization
Fig. 10.2 Typical voltage transfer (VTC) of a logic inverter .
Fig. 10.3 Definitions of propagation delays and switching times of the logic
inverter
Fan-In and Fan -Out
• Fan-in of a gate : number of inputs .
• Fan-out : maximum number of similar gates that
a gate can drive while remaining within
guaranteed specifications (to keep NMH above
certain minimum) .
10.2 Design and performance analysis of the CMOS inverter .
10.2.1 Circuit structure
Fig. 10.4 (a) The CMOS inverter and (b) its representation as a pair of
switches operated in a complementary fashion .
10.2.2 Static operation
10.2.2 Static operation
Fig. 10.5 The voltage transfer characteristic (VTC) of the CMOS
inverter when QN and QP are matched
10.2.3 Dynamic Operation
Fig. 10.6 Circuit for analyzing the propagation delay of the inverter
Fig. 10.7 Equivalent circuits for determining the propagation delays
10.3 CMOS Logic Gate Circuits
10.3.1 Basic structure
Fig. 10.8 Representation of a three- input CMOS logic gate
Fig. 10.10 Examples of pull –down networks (PDN)
Fig. 10.10 Examples of pull- up networks (PUN)
Fig. 10.11 Usual and alternative symbols for MOSFETs
10.3.2 The Two – Input NOR Gate
Fig. 10.12 A two – input CMOS NOR gate
10.3.3 The Two- Input NAND Gate
Fig. 10.13 A two-input CMOS NAND gate
10.3.4 A Complex Gate
10.3.5 Obtaining the PUN and the PDN and Vice Versa
Fig. 10.14 CMOS realization of a complex gate
10.3.6 The Exclusive- OR Function
Fig. 10.15 Realization of the exclusive –OR (XOR) function .
10.3.8 Transistor Sizing
Fig. 10.16 Proper transistor sizing for a four- input NOR gate
Fig. 10. 17 Proper transistor sizing for a four- input NAND gate
Fig. 10.18 Circuit for Example 10.2
10.4 Pseudo- NMOS Logic Circuits
10.4.1 The pseudo – NMOS inverter
Fig. 10.19 (a) The pseudo- NMOS logic inverter . (b) The enhancement load NMOS
inverter (c) The depletion- load NMOS inverter
Fig. 4-2 . The enhancement-type NMOS transistor
with applied voltage
The I-V characteristic of MOSFET
The n- channel depletion –type MOSFET
The depletion type n-channel MOSFET
10.4.2 Static Characteristics
Fig. 10.20 Graphical construction to determine the VTC of the inverter
Fig. 10.21 VTC for the pseudo- NMOS inverter .
10.4.4 Dynamic Operation