7.1 Name TWO characteristics of an ideal op amp - NSC Electrical Technology Electronics - Question 7 - 2016 - Paper 1

The term bandwidth refers to the range of frequencies over which an amplifier can operate effectively without compromising the linearity or quality of the output signal. It is defined as the difference between the upper and lower frequency limits where the amplifier's gain remains constant, typically to within a certain percentage of its maximum value, ensuring minimal distortion and loss of signal gain.

Positive feedback occurs when a portion of the output signal is fed back into the input of the amplifier in phase with the input signal. This results in an increase in the total input signal, which can lead to amplification. It is commonly used in applications such as oscillators or in circuits where a rapid response is desired, as it can drive the output to saturation, providing a fast switch-like behavior.

The circuit symbol for an operational amplifier consists of a triangle shape pointing to the right, with two input terminals (inverting and non-inverting) and one output terminal indicated. Additionally, the power supply connections are shown at the top and bottom of the triangle to indicate the positive supply voltage (+V) and negative supply voltage (-V).

For Figure 7.1, the input waveform is a sinusoidal signal with a defined amplitude and frequency. The output waveform, as shown in Figure 7.1, also maintains a sinusoidal shape, however, it is subject to an amplification factor.

In Figure 7.2, the input waveforms are again sinusoidal, and the output signals demonstrate phase inversion corresponding to the op-amp configuration. Ensure both sets of waveforms are represented on the same y-axis for clarity.

1. Increased Bandwidth: Negative feedback stabilizes the gain, allowing for a wider bandwidth in the amplifier's performance.

2. Reduced Noise and Distortion: By minimizing undesired signals and fluctuations, negative feedback can lower static and dynamic noise significantly, improving the overall fidelity of the output signal.

The op-amp configuration in Figure 7.3 is a non-inverting amplifier configuration.

The input signal is a sinusoidal waveform, and the output signal, which is also sinusoidal but amplified and in phase with the input, should be drawn on the same y-axis. The output waveform should be labeled clearly as 'Output' while the input waveforms should be labeled as 'Input'.

The voltage gain ($A_V$) of the non-inverting amplifier can be calculated using the formula:
$A_V = 1 + \frac{R_f}{R_{in}}$
Where:

• $R_f = 45 \text{ kΩ}$
• $R_{in} = 15 \text{ kΩ}$
  Thus, substituting the values: $A_V = 1 + \frac{45 \text{ kΩ}}{15 \text{ kΩ}} = 1 + 3 = 4.$

To calculate the output voltage ($V_{out}$), we use the formula:
$V_{out} = A_V \times V_{in}$
Given that $A_V = 4$ and $V_{in} = 2.5 V$, we have:
$V_{out} = 4 \times 2.5 V = 10 V.$

1. Tone Generators: Astable multivibrators are commonly used to generate audio tones in applications such as alarm systems and musical instruments.

2. Clock Pulse Generators: They can function as clock pulse generators in digital circuits to provide timing signals for sequential logic.

The input waveform depicted in FIGURE 7.5 is a trigger pulse shaped as a square wave. The output waveform from the astable multivibrator in FIGURE 7.4 is also a square wave that alternates between high and low states, effectively creating a square signal pattern that corresponds to the input pulse, ensuring clarity between both signals.

The feedback used in the RC phase-shift oscillator is positive feedback. This type of feedback is employed to sustain oscillations in the circuit.

One application of the RC phase-shift oscillator is as a tone generator in audio applications, frequently used to produce sound signals in synthesizers.

The oscillation frequency ($f_{osc}$) can be calculated using the formula:
$f_{osc} = \frac{1}{2\pi R C} \sqrt{\frac{1}{6}}$
Using:

• $R = 15 \Omega$
• $C = 150 nF = 150 \times 10^{-9} F$
  We find:
  $f_{osc} = \frac{1}{2\pi (15)(150 \times 10^{-9})} \cdot \sqrt{\frac{1}{6}} \approx 43.31 Hz$.

One application of the integrator circuit is in analog computing, where it is used to perform mathematical integration of input signals and generate corresponding outputs.

The input waveform for the op-amp integrator circuit is typically a triangular or ramp signal, which would result in a waveform that transitions between positive and negative values, exhibiting a linear integration characteristic over time, producing a square waveform at the output. Ensure to label both the input and output waveforms clearly.