Opamps Flashcards
Ideal Opamp characteristics
Input resistance RIN = infinity (input current zero)
The output resistance, Rout = 0
Open loop voltage gain is infinite, A= infinity
Zero common mode gain
Bandwidth = infinity
Characteristics are independent of temp.
The slew rate is infinite (The slew rate refers to how quickly the op-amp output voltage can change with time, usually given in V/μs )
Voltage gain of Inverting amplifier.
Vo/VI = - R2 / R1
Why is V’ = 0 ?
Because the non inverting input is earth, and the inverting input is Virtual Earth.
The opamp creates the virtual earth by setting an output and supplying the voltage through the two resistors.
What happens when an resistor is connected to the output of an inverting amplifier?
The opamp will supply (or drain) additional current in order to maintain the same output voltage and the virtual earth.
Do opamps draw current from the supply?
Yes they do, typically 1.7 mA, even when they are doing nothing.
What is the Golden Rule of opamps?
The opamp’s outputs do whatever is necessary to make the voltage difference between its inputs zero.
What is negative feedback and why is it necessary?
With negative feedback, a portion of the output is fed back to the input in order to oppose the change at the input.
In the inverting amplifer the R2 provides the negative feedback so that the opamp can create a virtual ground.
Without the
How can you change the input resistance of the opamp?
By adjusting the value of R1.
What is the equation of the output voltage for a summing amplifier?
What is the output sign of a Non-inverting amplifier?
The same as the input
How is the negative feedback supplied in a non-inverting amplifer
Provided by the potential divider (R1 and R2)
What is the voltage gain of a non-inverting amplifier?
What is the voltage follower?
Vo = VI
Used as a buffer stage to eliminate loading effects on the previous stage.
The transconductance amplifier
Also known as the voltage-current converter, the output current is controlled by the input voltage.
Transconductance = OutputCurren t/ Output Voltage
Transresistance Amplifier
Converts an input current to an output current
Convert an input current into a output voltage
Vo = -R2II
The integrator
Integrator: What is the output voltage expression?
What can this sort of integrator also be considered as ?
low pass filter
The integrator: Some of the problems?
The Integrator: Some solutions?
The differentiator equation
The differentiator: What would the output expression be with this input?
