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

Bandwidth refers to the range of frequencies over which an amplifier can operate effectively without distorting the output signal. It is measured as the difference between the upper and lower frequency limits where the amplifier maintains a specified level of gain, typically 3 dB down from the peak gain. This term is crucial as it defines how quickly an amplifier can respond to changes in the input signal.

Positive feedback occurs when a portion of the output signal is fed back into the input in phase with the original input signal. This mechanism can amplify signals and lead to increased gain but can also cause instability in systems, as well as oscillation if the gain exceeds unity. In many applications, positive feedback is utilized to achieve specific operational conditions like triggering and switching.

The circuit symbol for an operational amplifier consists of a triangle shape that represents the amplification function. Labels for the inverting (-) and non-inverting (+) inputs should be included at the base of the triangle, with output (V_out) denoted at the apex. Additionally, power supply terminals +V and -V should be drawn connected to the back of the triangle.

In the waveform diagrams:

• The input waveform should be depicted as a sine wave, labeled as $ext{V1}$.
• The output waveform should ideally show an amplified version of the input signal, also represented as a sine wave, labeled as $ext{V2}$, with proper notations for amplitude and phase relationships.

The op-amp configuration depicted in FIGURE 7.3 is a non-inverting configuration. This can be identified by the input being applied to the non-inverting terminal of the op-amp.

The input signal can be illustrated as a sine wave, which is applied directly to the non-inverting terminal. The output signal, also a sine wave, appears slightly phase-shifted and amplified, thus noted as $ext{V_out}$. Both signals should be labeled clearly with corresponding amplitude and timeframe incidences.

The voltage gain ($A_V$) for a non-inverting op-amp is given by:

$A_V = 1 + \frac{R_f}{R_i}$

Where $R_f$ is the feedback resistor and $R_i$ is the input resistor. In this configuration, using $R_f = 15 k\Omega$ and $R_i = 45 k\Omega$, we calculate:

$A_V = 1 + \frac{15 k\Omega}{45 k\Omega} = 1 + \frac{1}{3} = 1.33$

An astable multivibrator circuit can be utilized for various applications, including:

1. Tone Generator: This circuit generates audio tones for alarms or notifications.
2. Clock Pulse Generator: It is used in digital circuits to provide timing signals.

The input waveform represented in FIGURE 7.5 should be drawn as a square wave, indicating the trigger pulse behavior. The output waveform will demonstrate how the system responds to the trigger, typically showing alternating levels between +V and -V per cycle.

The feedback type used in the RC phase-shift oscillator is positive feedback. This allows for oscillation by reinforcing the input signals at the required phase shift.

One application of the RC phase-shift oscillator is as a tone oscillator, often used in sound generation for alarms and musical instruments.

The oscillation frequency ($f_{osc}$) for the RC phase-shift oscillator can be calculated using the formula:

$f_{osc} = \frac{1}{2\pi \sqrt{6} RC}$ where $R = 15\Omega$ and $C = 150 nF$. Thus,

$f_{osc} = \frac{1}{2\pi \sqrt{6} (15 \times 150 \times 10^{-9})} \approx 43.3 Hz$

One application of the op-amp integrator circuit is in analog computing, where it is used to perform mathematical integration of input signals over time.

The input waveform should be portrayed as a square wave. The output waveform will typically reflect the integration, showing a ramp-like behavior corresponding to the square wave input and returning to equilibrium after each cycle, with proper labeling of key points in the waveforms.