CH 5_BOOK_OPERATIONAL AMPLIFIERS Flashcards
What is an op amp?
An electronic unit that behaves like a voltage-controlled voltage source. It may also be regarded as a voltage amplifier with very high gain.
Op amps can also be used in making a voltage or current-controlled __________ source.
Current.
What can op amps do?
- Sum signals.
- Amplify a signal.
- Integrate a signal.
- Differentiate a signal.
What method do we use as a tool in analyzing ideal op amp circuits?
Nodal Analysis
List the different types of ideal op amp circuits covered in Ch 5.
- Inverter
- Voltage follower
- Summer
- Difference amplifier
An operational amplifier is designed so that it performs some __________ operations when external components, such as resistors and capacitors, are connected to its __________.
Mathematical, Terminals
An op amp is a passive or active circuit element?
Active
VIEW ONLY: A typical op amp.
What are the 5 important terminals of an op amp?
- Inverting input
- Non-inverting input
- Output
- Positive power supply (V+)
- Negative power supply (V-)
As an active element, the op amp must be powered by a __________ supply.
Voltage
VIEW ONLY: KCL equation for power supply currents
The output section of an op amp consists of a voltage-controlled source in __________ with the output resistance R_o.
Series
The input resistance R_i is the Thevenin equivalent resistance seen at the __________ terminals, while the output resistance R_o is the Thevenin equivalent resistance seen at the __________.
Input, Output
The differential input voltage V_d is given by what formula?
Where V_1 is the voltage between the inverting terminal and ground. And V_2 is the voltage between the non-inverting terminal and ground.
The op amp senses the difference between the two inputs, multiplies it by the __________ A, and causes the resulting voltage to appear at the __________.
Gain, Output
What is the formula for the output voltage?
A is called the “open-loop voltage gain” because?
It is the gain of the op amp without any exernal feedback from the output to the input.
VIEW ONLY: Typical ranges for op amp parameters.
A negative feedback is achieved when?
The output is fed back to the inverting terminal of the op amp.
What is the closed-loop gain?
When there is a feedback path from output to input, the ratio of the output voltage to the input voltage is called the closed-loop gain.
Why are op amps used in circuits with feedback paths?
Because as a result of the negative feedback, it can be shown that the closed-loop gain is almost insensitive to the open-loop gain A of the op amp.
A practical limitation of the op amp is that the magnitude of its output voltage cannot exceed what?
The input voltage.
(The output voltage is dependent on and is limited by the power supply)
The op amp can operate in which 3 modes? (Depending on the initial input voltage V_d)
VIEW ONLY: Op amp output voltage V_o as a function of the differential input voltage V_d. (Considering Saturation if circuit is not linear)
For Ch. 5, we will assume that op amps operate in the linear mode. This means that the output voltage is restricted by?
An op amp is ideal if it has which 3 characteristics?
VIEW ONLY: Ideal op amp model.
The 2 important properties of the ideal op amp are?
Which 2 extremely important equations can be derived from these 2 properties?
1) The currents into both input terminals are zero (because of infinite input resistance).
2) The voltage between the two input terminals is zero.
The 2 characteristics of an ideal op amp note that for voltage calculations the input port behaves as a __________ circuit, while for current calculations the input port behaves as a __________ circuit.
Short, Open
VIEW ONLY: The inverting amplifier.
The non-inverting input voltage is grounded, and the inverting input voltage V_i is connected to the input through R_1and the feedback resistor R_f is connected between the inverting input and output.
What is the goal in analyzing in inverting op amp?
To obtain the relationship between the input voltage V_i and the output voltage V_o.
Which equations can be derived from an inverting op amp? (View inverting op amp diagram)
Which 2 types of gain are associated with inverting op amps?
1) Closed-loop gain A_v
2) Open-loop gain A
What does an inverting amplifier do to the input signal?
An inverting amplifier reverses the polarity of the input signal while amplifying it.
With an inverting op amp, the gain is equal to?
Which means the gain depends only on the external elements connected to the op amp.
VIEW ONLY: The noninverting amplifier.
Which equations can be derived from a noninverting op amp? (View noniverting op amp diagram)
A noninverting amplifier is an op amp circuit designed to?
Provide a positive voltage gain.
Under what conditions does a noninverting op amp circuit become a voltage follower?
A voltage follower is useful for?
Such a circuit has a very high impedance and is therefore useful as an intermediate-stage (or buffer) amplifier to isolate one circuit from another, as seen on image. The voltage follower minimizes interaction between the two stages and eliminates interstage loading.
VIEW ONLY: The voltage follower.
What is a summing amplifier?
The summing amplifier is an op amp circuit that combines several inputs and produces an output that is the weighted sum of the inputs.
The summing amplifier is a variation of the __________ amplifier.
Inverting (can handle many inputs at the same time)
VIEW ONLY: The summing amplifier.
Which equations can be derived from a summing op amp? (View summing amp diagram)
Difference amplifiers are used when?
Difference amplifiers are used in various applications where there is a need to amplify the difference between two input signals.
What is a difference amplifier?
A device that amplifies the difference between two inputs but rejects any signals common to the two inputs.
Difference amplifiers are the first cousins of the ________ amplifier.
Instrumentation
VIEW ONLY: The difference amplifier
Which equations can be derived from a difference amplifier? (View difference amp diagram)
It is often necessary in practical applications to connect op amp circuits in __________ to achieve a large overall gain.
Cascade
What is a cascade connection?
A head-to-tail arrangement of two or more op amp circuits such that the output of one is the input of the next.
When the op amp circuits are cascaded, each circuit in the string is called a?
The original input signal is?
Stage, increased by the gain of the individual stage
Op amp circuits have the advantage that they can be cascaded without changing their?
Input-output relationships (due to the fact that each ideal op amp circuit has infinite input resistance and zero output resistance)
Since the output of one stage is the input to the next stage, the overall gain of the cascade connection is?
The product of the gains of the individual op amp circuits.
What caution must one take in designing cascaded op amp circuits?
VIEW ONLY: A three-stage cascaded connection.
The instrumentation amplifier is an extension of the __________ amplifier in that it amplifies the difference between its input signals.
Difference
An instrumentation amplifier typically consists of _____ op amps and _____ resistors.
3 op amps, 7 resistors
VIEW ONLY: (a) The instrumentation amplifier with an external resistance to adjust the gain, (b) schematic diagram.
Which equations can be derived from the instrumentation amplifier? (View instrumentation amp diagram)
VIEW ONLY: The instrumentation amplifier rejects common voltages but amplifies small signal voltages.
The instrumentation amplifier amplifies small differential signal voltages superimposed on larger common-mode voltages. Since the common-mode voltages are equal, they cancel each other out.
The instrumentation amplifier has which 3 major characteristics?
READ ONLY: The LH0036 instrumentation amplifier.
VIEW ONLY: Summary of basic op amp circuits.
READ ONLY: Op Amp Summary.
