ecen326: electronic circuits fall 2017spalermo/ecen326/bjt_amp_graph_design.pdf• isupply ≤ 1.5ma...
TRANSCRIPT
Sam PalermoAnalog & Mixed-Signal Center
Texas A&M University
ECEN326: Electronic CircuitsFall 2017
Lab 1 Graphical Design Approach
Common Emitter Amp w/ Emitter Resistor
2
GEeBBin
GEm
LCm
GEe
LCv
RRrRkkRR
RRgRRg
RRrRR
A
11
1
Typical Design Specifications
3
• Loaded voltage gain, Av
• Max output swing, vomax• This must be satisfied at a given linearity
(total harmonic distortion)
• Input resistance, Rin
• Power Supply, VCC
• Min Emitter Voltage for robustness, VE
How to set DC Biasing Conditions?
4
• In order to meet all design specifications, the DC biasing conditions (IC, RC) must be set appropriately
• Can transform design specifications into functions of IC & RC and graph them to find acceptable solution space
Rin, VCC, & Neg. vomax Specifications
5
• Rin Spec
• Input resistance is primarily set by RE||RG
inGE
GEGEeBBin
RRR
RRRRrRkkRR
11
Rin, VCC, & Neg. vomax Specifications
6
• Need a minimum VCE to keep transistor in active mode with maximum negative swing
margin.for 500set togoodoften isit enough, relaxed are specs theif Note*
300Set
min
min
mVV
mVV
CE
CE
mVVvRIVVRIvVVV
EoCCCCCE
CCoCEECC
300maxmin
maxmin
• VCC Spec (w/ max negative swing)
Rin, VCC, & Neg. vomax Specifications
7
• Can solve for IC
C
EoCCC R
VVvVI
3.0max
• Minimum negative AC Swing constraint sets an upper bound on IC
Pos. vomax Specification
8
• Need to insure with a positive swing that the output signal doesn’t clip the power supply
CCoCCCC VvRIV max
• Positive AC Swing constraint sets a lower bound on IC
• Additional linearity constraint (harmonic distortion) generally sets a tighter bound
C
oC R
vI max
Gain Specification
9
• Gain constraint sets a lower bound on IC
invLC
thv
GEvLC
thvC RA
RR
VARRA
RR
VAI
GE
th
C
LCth
C
GEm
LCm
i
ov RR
VI
RRVI
RRgRRg
vvA
11
Harmonic Distortion Specification
10
• Need a minimum amount of bias current to insure that the AC swing doesn’t distort
E
cbebbe
th
CQm
bebebebec
Rffivvvv
V
Iaga
vavavaavi
where Here
... ,21 , where
...
distorts which system a as a Model
221
33
221
*This analysis is for a general CE Amp, in our specific circuit RCRC||RLand RERE||RG
Harmonic Distortion Specification
11
... ,
121 ,
1
* thatshowCan ....
inputour is that because offunction a as express want toWe
3221
33
221
Emth
CQ
Em
m
bbbbc
bc
RgV
Ib
Rgg
b
vbvbvbbvi
vi
CQ
c
Emc I
iRg
ibbHD max
max21
2
11
41
212
is distortion harmonicorder -second The
• For single-ended amplifiers with low-distortion, HD2 will dominate the distortion terms *This analysis is for
a general CE Amp, in our specific circuit RCRC||RLand RERE||RG
Harmonic Distortion Specification
12
221 max
HDRRRvVI
inLC
othC
in
E
EC
othC
Eth
C
C
o
Em
C
o
C
CQEmc
RR
HDRRvV
I
RVIHD
Rv
RgHDR
v
I
IRgHDi
Using
221
24124
124ionspecificat HD2given asatisfy To
max
maxmax
max
• HD2 will dominate, but is not the only distortion term, so you need to use a slightly larger current or put some margin in the HD2 value relative to the THD spec
*This analysis is for a general CE Amp, in our specific circuit RCRC||RLand RERE||RG
Key CE Amp Design Equation Summary
13
221 :Distortion Harmonic
:Gain
:Swing Pos.
3.0 :V Rin, Swing, Neg.
max
max
maxCC
HDRRRvVI
RARR
VAI
RvI
RVVvVI
inLC
othC
invLC
thvC
C
oC
C
EoCCC
Design Example - Specifications
14
• |Av| |-20|
• Rin 10k
• Vomax = 1Vpk w/ THD ≤ 5% (-26.0dB)
• VCC = 5V
• VE ≥ 0.5V
• Isupply ≤ 1.5mA
• Nominal operation at 5kHz
Design Equation Plots
15
• Chosen design point is IC=1mA, RC=3k
Plots done with =150
DC Operating Points
16
• RE is set with VE=IERE
• RG is set as Rin/• DC bias points must be reasonable for the circuit
to work as designed!
AC Gain
17
• |Av| =30.4V/V
Rin
18
• Rin = 11.3k
Distortion
19
New Lab1 Design Specs
20
• |Av| |-15|
• Rin 5k
• Vomax = 1Vpk w/ THD ≤ 5% (-26.0dB)
• VCC = 5V
• VE ≥ 0.5V
• Isupply ≤ 4mA
• Nominal operation at 5kHz