simple rtl gates invertor - university of florida
TRANSCRIPT
ac flows here
ac gain = -20k/rE
KTeVsc
BEeII ~ Ω=C
E Ir 25
Recap: Ebers Moll model
Ic = (1.6V – 0.6V)/2kohm = 0.5 mA
To calculate rE, need quiescent value for Ic
rE = 50 ohm, ac gain = -20k/50 = 400 (not infinite)
Miller effect Decrease of gain at high frequency due to Cbc
Cbc
Cbc ~ a few pF
R
CVac
Output impedance R + C to ground RC filter
High or Low pass?
RCf db π21
3 =
For R = 1k, C = 2 pF, f3db ~ 1 MHz
In common emitter amplifier, Cbc is not connected to ground
Gain = -RC/RE
∆Vb = ∆Vin ∆Vc = -|Gain|∆Vin
∆Vcapacitor = ∆Vb - ∆Vc = (1+|Gain|)∆Vin
∆Q = Cbc ∆Vcapacitor = Cbc(1+|Gain|)∆Vin
Rc
RE
Vcc
capacitance appears much largerMiller effect: f3db lowered by (1+|Gain|)
Cbc