Transistor Digital Circuits - utcluj.ro · MOSFET DIGITAL CIRCUITS ... p and R Logic inverter....
Transcript of Transistor Digital Circuits - utcluj.ro · MOSFET DIGITAL CIRCUITS ... p and R Logic inverter....
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Transistor Digital Circuits
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Transistor – voltage-controlled current source
n-type p-type
•n -channelMOSFET
•npn BJT
•p-channel MOSFET
• pnp BJT
Non-linear controlled sources: square - MOSFET
exponential – BJT
Transistor - operating principle and regionsa brief remembrance
Treshold voltage
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Using Tn transistor
Output quantities: IO, VO
transfer characteristics:
IO(VCT), VO(VCT)
IT = IO
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Transfer Characteristics, Tn
• VCT<VThn, Tn – off, IO=IT=0
• VCT>VThn, Tn – on, IO=IT>0
VPS=RIO+VO ; VO= VPS- RIO
VCT , IO , VO
VO,min=0 R
VI PS
Oex
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• Two extreme regions, passive regions:
- cutoff (off) IO=0; VO>0; ideal switch in off state
- extreme conduction (exc) IO=IOex; VO=0; ideal switch in
the on state
If VCT < VThn or VCT > VCTex switching transistor
• An intermediary region, active forward region aF
VCT(VThn; VCTex) – permanent conduction (amplifier)
Tn
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Symbols of the transistors
G - gate or grid D - drainS - source
n-type p-type
n-channel enhancement-type MOSFET
p-channel enhancement-type MOSFET
B – baseC – collector E – emitter
npn BJT pnp BJT
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Controlled switch model
vCT >VCTex; T- (exc); iOT >0; vOT0
vCT <VThn; T- (off); iOT = 0; vOT=VPS
vCT >VThp ; T- (off); iOT =0; vOT=VPS
vCT <VCTex ; T- (exc) ; iOT >0 ; vOT0
The controlled switches are complementary
TpTn
Switching Transistor
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MOSFET DIGITAL CIRCUITS
➢ Ideal controlled switch model
➢ Implementation with MOSFET
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Logic inverter
0V logic 0
VPS logic 1
vA Tn vy
VCoL = 0 (off) VPS
VCoH = VPS (on) 0
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logic 0 - 0V
logic 1 - VPS
Tn and R Tp and R
Logic inverter
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Critical analysis of the logic inverter
With Tn and R
Disadvantage elimination:
R as small as possible, ideal R→0;
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Critical analysis of the inverter
withTn and R
Solution: replacement of R with a controlled switch
Disadvantage elimination:
R as small as possible, ideal R→0; R as large as possible, ideal R→∞
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Two possible solutions:✓ complementary switches
✓ same input
TTLCMOS
✓ complementary inputs
✓ same switch
MOS transitors BJT transitors and R
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CMOS Logic Inverter
vGSn=vI
vGSp=vI-VDD
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Logic function NAND, NOR
a) What is the truth table?b) What are the states of thetransistors?c) How can we eliminate the disadvantages due to the presence of R ?
Problems
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Logic function NAND, NOR
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CMOS NAND
a) What is the truth table?b) What are the states of alltransistors?
Problem
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CMOS NAND
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CMOS NOR CMOS AND
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20
Transfer characteristicof the CMOS inverter
Ideal (input) Real
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Noise margins
maxmax
minmin
OLILL
IHOHH
VVNM
VVNM
Voltage levels and
noise margins for
CMOS logic family
supplied at +5V
V1V5.0V5.1 LNM
V1V5.3V5.4 HNM
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BJT DIGITAL CIRCUITS
➢ RTL technology
➢ TTL technology
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Switching BJT, digitalcircuit
Resistor to limit the base current
B
Co
B
BECoB
R
v
R
Vvi
7.0
Cex
Bsat
ii
C
Al
C
CEsatAlCex
R
V
R
vVi
2.0
T – (off), if vCo< 0.6V
T – (on), if iB > iBsat
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Problem
V5;150
;k2;k100
Al
CB
V
RR
a) What is the state of T if vCo=0V?
What is the vCE value?
b) What is the state of T if vCo=5V?
What is the vCE value?
c) What is the vCo range to keep T off?
What about to keep it in saturation?
d) If 0V => logic 0 and 5V => logic 1,
what is the logic function of the
circuit if ]V}[5;0{Cov
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Bipolar Digital Circuits
• Inverter RTL Technology
• NOR
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a) What is the schematic for the 2-input NAND gate in a RTL technology?b) What is the truth table?c) What are the states of the transistors?
Problem
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TTL: Transistor-Transistor Logic
• Logic Inverter
• from technological reasons in TTL integrated circuits the use of only npn type transistors is preferred
• identical transistors but complementary control
vI1, vI2 ?
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Standard TTL gate OPTIONAL
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Voltage levels and noise margins for TTL family
Supply only with 5V
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TTL sub-families with improved performances
Schottky transistor Schottky diode: a metal to semiconductor junction, in conduction 0,5V
vBE=0,8V; vBC=0,5V; vCE=0,3V
• Schottky transistor doesn't enter saturation mode
• increases the commutation speed
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Simplified structure of a 2-input NAND gate from the Low-power Schottky family
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Analog Switch (AS)
The AS is an electronic circuit that allows or blocks an input signal to pass to the output of the circuit according to a control signal.
vCo - two levels: VCoL<VTh and VCoH>VCTex
vCo=VCoL ; Tn-(off) ; vO=0
vCo=VCoH ; Tn- (exc) ; vO= vI
no power consumption
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VThpVThn
Bidirectional AS with two complementary
controlled switches
vCo=VCoL ; AS - (off) ;
vCo=VCoH ; AS - (on) ;
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C=0; AS - off; vO=0
C=1; AS - on; vO=vI
IC 4066 –4 transmission gates; supplied at 10V, ron=150Ω
DG400 (Siliconics) ron=20Ω
VCoH=VDD; VCoL=VSS
vI (VSS; VDD)
AS
AS – CMOS implementationbidirectional transffer
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Application: three-channel MUX
What is the output voltage in each of the three situations? Justify the answer.
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Application: three-channel MUX