7.1 Explain what an operational amplifier (op amp) is - NSC Electrical Technology Power Systems - Question 7 - 2017 - Paper 1

1. Integrated circuits are cheaper to manufacture due to the smaller size and reduced amount of material used in their production.
2. They enable a high level of integration, which allows for fewer external components to be needed in a circuit, enhancing reliability and performance.

A differential amplifier amplifies the difference between two input voltage signals. It takes the voltage at one input and subtracts the voltage at the other input, resulting in an output that represents the difference. This makes it useful in applications where common-mode signals need to be rejected, such as in instrumentation and audio applications.

Negative feedback.

Positive feedback.

Positive feedback enhances or increases the output signal, reinforcing the input signal, whereas negative feedback reduces the gain of the system by feeding a portion of the output back to the input in the opposite phase, enhancing stability and reducing distortion.

Using the formula:
V_{OUT} = rac{R_f}{R_{in}} imes V_{in}
where:

• $R_f = 170 \, k\Omega$
• $R_{in} = 10 \, k\Omega$
• $V_{in} = 0.7 \, V$
  The output voltage is:
  V_{OUT} = rac{170k}{10k} imes 0.7 = 11.9 \, V.

The voltage gain (A) is given by:
A = rac{V_{OUT}}{V_{in}} = rac{11.9 \, V}{0.7 \, V} = 17.0.

1. Audio signal processing.
2. Active filters in electronic circuits.

To clean noisy signals in digital systems.

A monostable multivibrator has one stable state and outputs a pulse width signal when triggered. In contrast, a bi-stable multivibrator has two stable states and remains in one state until triggered to switch to the other.

The input waveform consists of multiple overlapping sine waves. The output waveform, when drawn below, will be a sawtooth or square wave that reflects the summation of the input signals.

Using the formula:
V_{OUT} = -rac{R_f}{R_{in}} imes V_{in}
where

• $R_f = 200 \, k\Omega$
• $R_{in} = 20 \, k\Omega$
• $V_{in} = 5 \, V$
  Thus,
  V_{OUT} = -rac{200k}{20k} imes 5 = -50 \, V.

Using the gain formula:
Gain (A) = -rac{R_f}{R_{in}} = -rac{200k}{20k} = -10.

To implement another type of multi-vibrator which converts noisy signals into clean digital signals.

f = rac{1}{2 \pi \sqrt{LC}}
where

• $L = 27 \, mH = 27 \times 10^{-3} H$
• $C = 47 \, \mu F = 47 \times 10^{-6} F$
  Therefore, the resonant frequency is:
  f = rac{1}{2 \pi \sqrt{27 \times 10^{-3} \times 47 \times 10^{-6}}} = 141.28 \, Hz.

f = rac{1}{2 \pi RC}
where

• $R = 25 \, k\Omega$
• $C = 45 \, \mu F$
  Thus,
  f = rac{1}{2 \pi (25 \times 10^3) (45 \times 10^{-6})} = 57.76 \, kHz.