There is a small resistance when looking into
a voltage source
You can model a voltage
source in series with a resistor between any two terminals in a linear network
In finding a Thevenin
equivalent circuit, short circuit all independent voltage sources
The Norton
current between and is
The Thevenin
resistance between and is
The Thevenin
voltage between and is
The value of should be much larger than for maximum voltage transfer to the load
If a certain two
port network has as one of its admittance paramaters, should be
The 3 dB frequency
Is where the gain is reduced
by approximately 70%
Is where power is reduced by
half
Is where power is reduced by
3 dB
For a transfer function which
has two poles at 500 & 200000, and two zerosat 10000 & 15000, the pole at 500
Will reduce the magnitude of
the gain by 20 dB per decade from 500 onwards
Will introduce a phase shift
of 45 degrees at 500
Will
introduce a phase shift of 49 degrees at 5000
For a transfer
function , the gain
magnitude at is approximately
For a transfer
function , the bandwidth is
With an (ideal) op-amp
The inverting and
non-inverting inputs are at virtual ground
No current flows into the
input of the op-amp
It is direct coupled
Very large open-loop gain
Infinite bandwidth
Very large input resistance
The compensation capacitor provides
the op-amp stability by creating a dominant pole
Suppose the unity
gain frequency of a particular op-amp with an internal compensation
capacitor is .
When configured
as a non-inverting amplifier with a gain of 100, the bandwidth would be
When configured
as an inverting amplifier with a gain of -100, the bandwidth would be
Suppose the unity
gain frequency of a particular op-amp with an internal compensation
capacitance of is . The unity gain
frequency would change to be larger than if the compensation capacitor were to be
changed to
DC imperfections result in
Input offset voltage
Input offset current
Input bias currents
Output offset voltage DC
imperfections in non-ideal op-amps are caused by a mismatch in
input transistors
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Electrons in
the conduction band and valence band are responsible for current conduction in silicon
By convention, the direction
of current is assumed positive in the direction to which holes flow
In intrinsic silicon
The concentration of holes
and electrons are dependent by temperature
The concentration of holes
and electrons are equal
Hole movement is achieved by
valence
electrons hopping and filling holes
To form n-type silicon,
intrinsic silicon can be doped with phosphorus
To form p-type silicon,
intrinsic silicon can be doped with aluminium
In doped silicon, the
concentration of free carriers are controlled by the doping
concentration
In an extrinsic
semiconductor, if the doping concentration is
The concentration
of majority carriers is approximately
The concentration
of monitory carriers is inversely related to
Current flow in
semiconductors is achieved by
Applying an electric field
Concentration gradient in
free carriers
A n-type doped silicon is more
conductive than
a p-type doped silicon
When an n-type doped silicon
and p-type doped silicon is brought together and diffusion is possible
across the contact area
Holes diffuse from the
p-type to the n-type piece
Holes recombine with
electrons in the n-type piece
A depletion region is
created across the PN junction with similar widths in each piece
The potential barrier created
within the depletion region
Depends on temperature
Depends on the majority
carrier concentrations in the p-type and n-type
The width of the depletion
layer
Gets narrower as the
majority concentrations increase
Gets wider when the PN
junction is reverse biased
Drift current does not increase when a PN junction
is reverse biased
Diffusion current reduces when a PN junction is
reversed biased
A forward biased PN junction results in a
higher diffusion current
In a forward biased PN
junction, the forward current is caused by
Holes injected from P to N
Electrons injected from N to
P
Recombination of holes with
electrons in the N type
Recombination of electrons
with holes in the P type
The recombination of holes
with electrons in the N type piece of a PN junction
Contributes to the majority
carrier forward current flow
Decreases exponentially with
distance from the edge of the depletion layer
Is equal to the diffusion
current of holes in the N type
The forward current starts to
increase exponentially once the knee voltage (of around 0.5-0.7V) is
exceeded
Zener diode breakdown occurs
before avalanche breakdown
The junction may break down
if a large reverse voltage is applied
For a BJT
The base must be thin
The Base-Emitter junction
must be forward biased
The Base-Collector junction
must be reverse biased
Doping concentration of the
emitter is significantly higher than the base and collector
BJTs usually operate in forward
active mode
For a BJT biased in forward
active mode, the typical voltage between the base and emitter is around 0.7 V