Operational Amplifiers Concepts

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Questions and Answers

What type of amplifier is used as the output stage of an op-amp?

  • Single-ended amplifier
  • Push-pull power amplifier (correct)
  • Differential amplifier
  • Class A amplifier

The non-inverting input of an op-amp is denoted with a minus (-) sign.

False (B)

What causes slight mismatches in the transistors of an op-amp?

Unequal input bias currents

In an ideal op-amp, no current is ______ from the input signal.

<p>drawn</p> Signup and view all the answers

Match the Op-Amp parameter to its description:

<p>Input Bias Current = Direct current absorbed by op-amp inputs Offset Current = Difference between input currents Input Offset Voltage = Minor voltage difference between the inputs CMRR = Common-Mode Rejection Ratio</p> Signup and view all the answers

What does the slew rate (SR) represent in an operational amplifier?

<p>The maximum rate at which the output voltage can change. (A)</p> Signup and view all the answers

Slew-rate limiting occurs when the slope of the sine wave is greater than the slew rate (SR).

<p>False (B)</p> Signup and view all the answers

What is the typical slew rate value for the IC 741 op-amp?

<p>0.5 V/µs</p> Signup and view all the answers

When the initial slope of the sine wave is greater than the slew rate, it leads to slew-rate __________.

<p>distortion</p> Signup and view all the answers

Match the following terms with their descriptions based on the content provided:

<p>Slew Rate = Maximum rate of output voltage change Slew-rate Limiting = Output follows input up to a point and then flattens out Slew-rate Distortion = Output becomes triangular due to high input slope Open Loop Gain = Gain of an amplifier without feedback.</p> Signup and view all the answers

What is 'input offset current' a measure of in an operational amplifier?

<p>The difference between the biasing currents of inverting and non-inverting inputs (B)</p> Signup and view all the answers

Input offset voltage is the error voltage that occurs when the inputs of an op-amp are grounded, resulting from differences in the $V_{BE}$ values of input transistors.

<p>True (A)</p> Signup and view all the answers

What is the formula for calculating Common Mode Rejection Ratio (CMRR)?

<p>$CMRR = \frac{| A_d |}{ | A_C |}$</p> Signup and view all the answers

The input offset current is generally specified for ______ output voltage at 25°C temperature.

<p>zero</p> Signup and view all the answers

Match the following terms with their descriptions:

<p>Input offset current = Difference in biasing currents of input transistors Input offset voltage = Error voltage when inputs are grounded CMRR = Ratio of differential to common-mode gain</p> Signup and view all the answers

Flashcards

Input offset current

The difference in biasing currents between the inverting and non-inverting inputs of an operational amplifier.

Input offset voltage

A small error voltage at the output of an op-amp when its inputs are grounded, caused by the difference in $V_{BE}$ values of input transistors.

Common Mode Rejection Ratio (CMRR)

The ratio of differential voltage gain to common mode voltage gain in an operational amplifier.

Differential Voltage Gain ($A_d$)

The gain of an op-amp for the difference between its inputs.

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Common Mode Voltage Gain ($A_c$)

The gain of an op-amp for a signal applied equally to both inputs.

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Input Bias Current (IB)

The input current required to properly bias the transistors in the first stage of an operational amplifier. In an ideal Op-Amp, no current is drawn from the input signal.

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Slew Rate

The maximum rate of change of the output voltage of an operational amplifier. It's a measure of how fast the output voltage can change, usually expressed in volts per microsecond (V/µs).

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Slew-rate Limiting

When a signal's rate of change is faster than the op-amp's slew rate, the output gets delayed, resulting in a distorted signal.

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Slew-rate Distortion

The effect on the output signal when the input signal changes too fast for the op-amp to handle. Causes the output to become triangular instead of sinusoidal.

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Open-loop Gain

The gain of an op-amp when no feedback is applied. It's typically very high, but decreases with increasing frequency.

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Compensation Techniques

Internal techniques used to control the op-amp's frequency response and stability. They affect the overall performance and output.

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Study Notes

Operational Amplifiers

  • Operational amplifiers (op-amps) have two input terminals (inverting and non-inverting) and one output terminal
  • In a differential amplifier, the first stage produces opposite changes in the collector currents of the transistors
  • When the amplified signal passes from either of the transistor stages, the output of the op-amp may be out of phase with the input signal
  • The input for which the output is in phase with the input is called the non-inverting input; the applied signal is denoted by the (+) sign
  • the input for which the output is out of phase with the input is called the inverting input; denoted by the (-) sign
  • The output voltage (Vo) is zero

Input Offset Current

  • Input bias current (Ib): In an ideal op-amp, any current drawn from applied input signal is practically absorbed by the transistors, but in practical op-amps, a small amount of direct current to bias the transistors in the first differential stage is required
  • The input bias currents (Ib) are not equal to each other due to slight mismatch of transistors
  • Therefore, input bias current is not equal to the defined input bias current

Input Offset Voltage

  • The input offset voltage (Vio) is equal to the difference in voltage values of input transistors.
  • This voltage must be applied to particular input terminals to obtain zero output voltage
  • This is called as 'offset compensation'

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