l25 04/16/021 ee 4345 - semiconductor electronics design project spring 2002 - lecture 26 professor...
TRANSCRIPT
L25 04/16/02 1
EE 4345 - Semiconductor Electronics Design Project Spring 2002 - Lecture 26
Professor Ronald L. [email protected]
http://www.uta.edu/ronc/
L25 04/16/02 2
Fig 5.1* Emitter-follower outputstage with current-mirror bias.
• Q3 is gummel conf• IR~(VCC-Vbe)/(R3+R1)• IQ ~ IR*R1/R2• If Q1 & Q2 FA, thenVi = Vo +
Vt ln((IQ+Vo/RL)/IS)• If RL large, Io << IQ, so• Vi > 0, Vi = Vo + const.,
until Q1 saturates• Vi < 0, the same until
Q2 sat at -VCC +VCE2sat
• RL starts significant conduction at
RL3 = (2VCC + VCE2sat)/IQ
L25 04/16/02 3
Fig 5.2* Transfer char. of the circuit of Fig 5.1 for low (RL2) and high (RL1) values of RL• For RL = RL1 >
RL3, negl load curr
• For RL = RL2 < RL3, incl load curr
L25 04/16/02 4
Fig 5.3* (a) Q1 doesn’t cutoff(b) Q1 does cutoff
• (1) low input• (2) input high
enough, or RL low enough to c/o Q1
L25 04/16/02 5
Fig 5.4* Loadlines for RLs(2VCC + VCE2sat)/IQ RL3
• Gives max power (C) • RL2 < RL3 power (B) • RL1 > RL3
power (A) max =(1-VCEsat/VCC)/4 ~ 1/4
KVL gives:VCC =Vce1 +(IC1-IQ)*RL
IC1 = (VCC-Vce1)/RL+IQ
L25 04/16/02 6
Fig 5.6*
Max powerLoad, tang.@ mid-point
o.c. load
Short Circuit load
Constant power hyperbolas
2Vcc > BVCEO
L25 04/16/02 7
Fig 5.7* Low-frequency, small-signal equivalent circuit for the emitter follower
Class A: Drive device has an appreciable current(no-cutoff)
Av = vo/vi = RL/(RL+1/gm+Rs/o)
Ro = 1/gm+Rs/o
(… + RL)
L25 04/16/02 8
Fig 5.10* Simplified ic Class B output stage• Q1 (npn) and Q2 (pnp),
are a complementary pair 1 = 2
• Q1 off if Vi < VbeOn
• Q2 off if Vi > -VbeOn
Dead zone: IL = 0 if -VbeOn < Vi < VbeOn
IL
L25 04/16/02 9
Fig 5.11* Transfer Characteristic of the Class B Stage
L25 04/16/02 10
Fig 5.13* Class AB output stage. The gummel diodes reduce crossover distortion.
L25 04/16/02 11
Fig 5.20a* Simplified schematic of the 741 output stage
Group Project will be similar
Optimize current, voltage gain, fT
Use Cadence to capture schema- tic, set bias, etc. and gene- rate outputs
L25 04/16/02 12
References
* Analysis and design of analog integrated circuits, 4th ed., by Gray, Hurst, Lewis and
Meyer, Wiley, New York, ©2001.