Electronics - class-XII

Slew rate describes the time delay the opamp offers to changes in input voltage. Thus a change of 100V will take 10 micro second in the output to describe.

1.The oscillator circuits consists of a negative gain op-amp and a three section $RC$ network that produced the $180^{o}$phase shift.The phase shift network is connected from op-amp output back to its inverting input.

For an ideal op-amp, the input impedance $R _i$ is infinite, so, we can say that the input resistance of op-amp is very high.

If the signal is through the inverting terminal, output will appear 180 degrees out of phase, while if the input is through the non-inverting terminal, output will be in phase with the input

Their voltage gain is non uniform for a range of frequencies

An operational amplifier (op-amp) is an integrated circuit consisting of many transistors, resistors, and capacitors designed to perform mathematical operations.

In a differential amplifier configuration, an input applied to one terminal results in outputs at both terminals that are equal in magnitude but opposite in phase (polarity).

The maximum operating frequency of an op-amp is limited by its bandwidth, slew rate, and unity-gain bandwidth, as these parameters define how fast the output can change and the frequency range over which it can amplify.

An ideal operational amplifier is characterized by very high open-loop gain and a very wide bandwidth, allowing it to be used in various applications with feedback.

A typical operational amplifier has very high input impedance (often in the range of Mega-ohms or Giga-ohms) and low output impedance (typically less than 100 ohms).

Given,

In any adder circuitry of Op-amp, the output voltage must be equivalent to the summation of all input voltages where each input voltage is a multiple of constant gain factor. This circuit is usually more similar to inverting scalar type of amplifier with an exception of possessing more than one input. Therefore, output voltage of adder or summer Op-amp is phase inverted.

Referring to subtractor, integrator and differentiator amplifiers, the output voltage of subtractor deals with the difference between two input signals, while integrator generates its output voltage in terms of integral of input voltage whereas the output voltage of differentiator is proportional to change in input in accordance to time.

Slew rate is limited by the internal current available to charge compensation capacitors and the saturation of internal stages when driven by high-frequency or high-amplitude signals.

Unity Follower circuit provides buffering or can be also used as an isolation amplifier which has a provision to obtain a gain at unity despite the requisite of any phase reversal. Emitter follower circuit is also semantic to unity follower only with an exception of gain which is in very much proximity of being absolutely equal to 1 (unity level). 

Unity Follower is supposed to be used as buffer since it becomes quite feasible to transfer the input voltage in the form of output voltage along with the prevention of load resistance from loading down to input source simultaneously. This becomes possible because the value of input resistance tends to infinity & output resistance equals to zero.

An electronic oscillator is essentially an amplifier that uses positive feedback to sustain oscillations without an external input signal.

Voltage gain and output voltage are related by the formula $A _v=\dfrac{output \ voltage}{input \ voltage}$. Substituting the value of input voltage, we get, output voltage = - 20 x 20mV = -400 mV

 An ideal op-amp has infinite bandwidth. Therefore, any frequency signal from 0 to $\infty$ Hz can be amplified without attenuation.

The ideal opamp voltage is maintained constant. It is controlled by the input voltage. Thus the output of an opamp is controlled by the source (input) voltage

In an ideal opamp, output follows the input instantly and hence the time delay is zero. slew rate is calculated as the ratio of change in voltage at the output to time taken for this action to take place. If time delay is zero, the slew rate will be infinite

maximum voltage that can obtained will be equal to the supply voltage w.r.t ground and beyond which the amplifier will saturate

In an ideal op-amp circuit, the gain is independent of the frequency of the input signal within the bandwidth. If the 1000 Hz signal is amplified by 20 times, other signals within the bandwidth will also be amplified by the same factor.

The ideal op-amp has infinite high input resistance and infinite voltage gain.

Open loop voltage gain is given by $A _v=\dfrac{V _0}{V _+-V _-}$. If $V _+=V _-$, Voltage gain becomes infinity or very high. thus voltage gain increases

An ideal op-amp exhibits zero output resistance so that output can drive an infinite number of other devices.

Since input impedance for an ideal opamp is infinite, the current drawn will be zero 

a voltage follower is a circuit, wherein the magnitude and the phase of the signal remains the same. In order to achieve it, the feedback signal should be fed to positive terminal, so that phase is unchanged and the absence of a feedback resistor makes no loss in the output signal

The input impedance of an ideal opamp is infinite and hence the current through it is zero. Thus the voltage across the terminals is also zero

Increasing the supply voltage to an op-amp generally allows for a larger output swing (increasing gain potential) and increases the quiescent power consumption of the device.

Open loop gain of an amplifier is the ratio of output voltage to the input voltage difference that is being amplified.

The significant AC parameters of Op-amp are transient response, bandwidth and slew rate but all of them have different results while becoming excessive. The transient response affects the settling time while slew rate give rise to distortion if exceeded. As a result, bandwidth reduces the output voltage when it is exceeded. 

Since bandwidth is a small signal phenomenon, it represents the band of frequencies for which the gain remains constant & also highly dependable on compensating components including closed loop gain. But, it exhibits adverse consequences in the reduction of an output voltage when exceeded to greater extent.

Open loop voltage in an opamp is very high and hence option d is the correct option

Differential amplifiers are designed to amplify the difference between two signals (highly amplified) while rejecting signals common to both inputs, such as noise (common-mode rejection, slightly amplified).

1. Virtual ground refers to a circuit elements that is not connected to the ground directly, it is held at a reference voltage. This reference voltage need not to be same voltage as ground either.
   2. While in all other ground it may be mechanical A.C or an ordinary ground it act as a reference point against which other voltage can be measured.
   3. The key point  is that the current flow from one point of the circuit through ground then back into the circuit.
   So, current cannot flow to ground through a virtual ground.

Open loop configuration of Op-amp may increase the threat of distortion as well as clipping of output signal. Due to this reason, the output gets switched between the positive and negative saturation levels.

Hence, this is the major drawback because of which it is highly impossible to use Op-amps with open loop configurations in linear circuit applications.

the closed loop gain is given by $A _{cl}=\dfrac{A}{1+A \beta}$. since the open loop gain is large, the closed loop gain almost remains a constant, as it will be independent of open loop gain 

Input current in an ideal operational amplifier   $i = \dfrac{V}{Z}$
Since,  input impedance of the ideal operational amplifier is infinite  $i.e. Z = \infty$
$\implies \ i =\dfrac{V}{\infty}= 0$