Simple RTL gates

invertor

A B

NOR

011

010

001

100

QBA

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