EE 308 Quiz 2
Gm-C integrator is constructed using actively-loaded BJT diff pair with tail current of 25uA and capacitor with value 50pF. The unity-gain frequency of this integrator is approximately:
(1/2pi)(gm/C) = 1.53kHz
The load of a CC amplifier is 10kohms. If the B of a BJT is 100, then the input resistance of the CC must be on the order of
(B/gm)*gm*(RL) = 100*10k = 1Mohm
Two-stage (miller) integrator is constructed using: actively loaded BJT diff pair with tail current of 25uA, capacitor 50pF, and a CE stage. The frequency of RHP zero is 10 times larger than the unity-gain frequency of the integrator. The bias current of the CE stage is approximately:
125uA
Push-pull amplifier uses one npn and one pnp. The dead zone of this amplifier is approximately:
2Vbe = 2*(700mV) = 1400mV
The load of a CC amplifier is 3kohms. If the biased current is 1mA, the maximum output swing with no clipping is:
3k*1m = 3Vpp
The output resistance of a simple current mirror is 150k. Two resistors of equal value are inserted in the emitters. If the voltage drop over these resistors is 75mV, the output resistance of the modified topology is approximately:
4*150k = 600k
CC amplifier drives 10kohms and exhibits input resistance of 500kohms. If a load of 15k is presented, the input resistance of this same CC circuit will become approximately:
750kohms
This single-transistor amplifier has current gain of approximately unity:
CB
These single-transistor amplifiers have large (compared to 1/gm) output resistance:
CB and CE
This single-transistor amplifier has voltage gain of approximately unity:
CC
These single-transistor amplifiers have large (compared to 1/gm) input resistance:
CC and CE
This single-transistor amplifier is best characterized as a transconductor:
CE
These single-transistor amplifiers must be cascaded to produce a circuit that behaves as a voltage-controlled voltage source
CE and CC
A CMRR can be defined for this type of an amplifier:
Differential Pair Amplifier
MOSFET-based diff pair has a tail current of 100uA. gate overdrive of each device is 250mV. The transconductance that relates id to Vin has this approximate value:
Gm = 2*Id/Vov = 2*50uA/250mV = 0.4mA/V
An op-amp uses a two-stage miller integrator. The integrator consists of actively loaded diff pair with tail current of 25uA, cap 50pF, and CE stage. The slew rate of this op-amp is no larger than:
I(tail)/C = 0.5V/us
It is claimed that an amplifier behaves as a VCVS. This therefore must be true regarding its input and output impedances:
Large input impedance, small output impedance
The so-called coupling and by-pass capacitors determine this frequency:
Low-frequency 3dB cutoff
To construct "Darlington pair" these type of devices are needed:
NPN and NPN or PNP and PNP
To construct "Sziklai pair" these type of devices are needed:
NPN and PNP
The advantage of push-pull CC over a "regular" CC is:
No power dissipated when input is missing and no Vbe drop at the output.
The "small-signal" behavior of a BJT in forward-active can be characterized by Rpi, Ro, and 1/gm. For any practical device, this one is the largest:
Ro
These are (some) of the similarities between CE amplifier and CB amplifier
Rout ~ Rc, Collector is the output, High Rout.
CE amplifier has gm(eff) of 20mA/V and B = 50. The input resistance is no larger than:
Rpi = B/gm(eff) = 2.5kohms
High gain amplifier consists of two CE stages connected in cascade. The output of the first feeds the input of the second. Which CE stage is more likely to feature emitter degeneration?
Second stage, to increase its input linear range
A trans conductor is another "name" for this type of dependent source:
VCCS
The differential-input linear range of a BJT diff pair is approximately:
Vt = 26mV
To create differential-input trans conductor these type of circuits are needed:
current-mirrors
Op-amp with GBW of 2MHz implements a non-inverting amplifier with gain of 25mV/mV. The 3-dB corner frequency of this amplifier is approximately:
f3dB = GBW/Av = 80kHz
This amplifier type might experience cross-over distortion
push-pull
