Transcript Charge

Operational Amplifiers
The operational amplifier, also know as an op
amp, is essentially a voltage amplifier with an
extremely high voltage gain.
One of the building blocks for the
construction of analog electronics systems.
It may be combined with various external
components for a wide variety of purposes.
Operational Amplifiers
They are usually
fabricated as an
integrated circuit, an
array of transistors,
resistors, and
capacitors, on a single
silicon chip.
DIP – dual in-line
package is the most
common package form.
Operational Amplifiers
An ideal amplifier is defined as:
vout  Av vin
Ideal Operational Amplifiers
An op amp is built as a differential amplifier, where
the output voltage is defined as the product of the
gain with the voltage difference between of the
amplifier’s two inputs.
This means that any stray noise appearing on both
inputs are cancelled, and only the voltage difference
is amplified.
Ideal Operational Amplifiers
It has two inputs:


v+ - the non-inverting input;
v- - the inverting input.
The currents through the inputs are zero, due to fact
that an ideal op amp’s has infinite input resistance.
The output voltage given by the open loop gain is
defined below:
Negative Feedback
Negative feedback is required to make a
large class of useful circuits with op
amps. It is achieved when the output
voltage, vo , is connected through a
network to the inverting input of the op
amp.
Negative Feedback
The provision that the open loop gain
approaches infinity and negative feedback,
allow us to assume that the voltage at the
“-” input terminal is driven to to same
voltage as that applied at the “+” input
terminal.
v  v
Closed Loop Gain
The negative feedback connection
closes the loop, which allows us to
compute the closed-loop gain, AF , for
circuits containing such feedback loops.
Power Supply Voltage Constraint
The output voltage of an op amp cannot
exceed the supply voltage applied to
operate the op amp.
VSS  vo  VDD
Summary
An ideal op amp with feedback,
assumes:
i = i- = 0
v- = v+
Vo is bounded by the power supply voltage.
 +


Non-inverting Amplifier
The input of the
amplifier is made to
the non-inverting
input.
The closed loop gain
is:
R
AF  1 
2
R1
The output is not
inverted.
Unity Gain Buffer
The input of the
amplifier is made to
the non-inverting
input.
The closed loop gain
is:
AF  1
The output is not
inverted.
Inverting Amplifier
The input of the
amplifier is made to
the inverting input.
The closed loop gain
is:
R2
AF  
R1
The output is
inverted.
Differential Amplifier
The input of the
amplifier is made to
both inputs.
The closed loop gain is:
vo  
R2
v1  v2 
R1
The output is inverted.
Summing Circuit
The input of the
amplifier is made to the
inverting input.
The closed loop gain is:
 R2
R2 
vo   
viA 
viB 
R1B 
 R1 A
The output is inverted.
Integrator Circuit
The input of the
amplifier is made to the
inverting input.
The closed loop gain is:
1 t
vo  
vi dt  vo 0 

R1C 0
The output is inverted.
Active Filters
Filter is a network that is frequency
selective.
Passive filters uses only passive
components such as: resistors,
capacitors, and inductors.
Active filters uses amplifiers to achieve
higher performance.
Active Filters
The complex voltage
gain is the ratio of the
phasor transforms of
the output and input
voltages.
vo
Z2
AF 

vi
Z1
Z2 
1
jC 
1
R2
Z1  R1
R2
R1
AF  
1  jR2C
Where  HI 
1
R2C
Current-to-Voltage Converter
Some applications
require that a
current be converted
to a voltage, and
this can be
accomplished with
an op-amp.
ii  i f
vo  ii R