7.1 State THREE ideal characteristics of an operational amplifier (op amp) besides unconditional stability - NSC Electrical Technology Electronics - Question 7 - 2016 - Paper 1

Unconditional stability refers to the ability of an operational amplifier to operate without oscillation or instability under any condition. This means the amplifier will not be affected by external factors such as temperature variations or circuit component changes.

Positive feedback occurs when a portion of the output signal is fed back into the input in phase with the original input signal. This can result in an increase in the output signal and is often used in applications like oscillators.

An oscillator circuit uses positive feedback to maintain continuous oscillation.

1. Negative feedback reduces distortion and increases the linearity of the amplifier, resulting in improved signal fidelity.

2. It enhances the stability of the amplifier by reducing its gain sensitivity to variations in temperature and component values.

As this requires drawing, please refer to the standard representation of an ideal op-amp output where the output follows the input signal amplified indefinitely (ideal case).

The circuit is an inverting op-amp configuration.

As this requires drawing, please sketch the original input sine wave and the output sine wave, which will be inverted and amplified according to the gain determined by the resistors in the circuit.

The voltage gain (A_V) can be calculated using the formula:

$A_V = -\frac{R_F}{R_{in}}$

Where $R_F$ is the feedback resistor and $R_{in}$ is the input resistor. Thus,

$A_V = -\frac{12000}{2200} = -5.45$

The output voltage ($V_{out}$) can be calculated using the formula:

$V_{out} = A_V \times V_{in}$

Where $A_V = -5.45$ and $V_{in} = 5V$. So,

$V_{out} = -5.45 \times 5 = -27.25V$

If $R_F$ decreases, the voltage gain of the op-amp will also decrease because the gain is directly proportional to the feedback resistor. This results in a lower output voltage for a given input signal.

The summing op-amp circuit allows for the combination of multiple input voltage signals into a single output voltage. It sums the input voltages while inverting the phase, producing an output that is the sum of the input signals' voltages.

The output voltage ($V_{out}$) can be expressed as:

$V_{out} = - (V_1 + V_2 + V_3)$

Given the values $V_1 = 2V$, $V_2 = -10V$, and $V_3 = 5V$:

$V_{out} = - (2 - 10 + 5) = -3V$

The function of the monostable multivibrator circuit is to generate a single output pulse of a defined width in response to a trigger pulse.

As this requires drawing, please sketch the input trigger pulse with a square wave representation alongside the corresponding output pulse showing the timing delay.

The time delay ($t$) can be calculated by:

$t = 5 \times R \times C$

Substituting the given values:

$t = 5 \times 12000 \times 47 \times 10^{-6} = 2.82 s$

The frequency ($f_R$) can be calculated using the formula:

$f_R = \frac{1}{2\pi\sqrt{6RC}}$

Using $R = 10 kΩ = 10 \times 10^3 \Omega$ and $C = 250 pF = 250 \times 10^{-12} F$:

$f_R = \frac{1}{2\pi\sqrt{6 \times (10 \times 10^3) \times (250 \times 10^{-12})}} = 41.09 Hz$

In a differentiator circuit, the op-amp produces an output that is proportional to the rate of change of the input signal. This means it amplifies the difference between the input voltage over time, creating an output that can represent the slope of the input waveform.

Op-amps are typically packaged as integrated circuits in a hard plastic body, which includes external pins for connection to circuits. Some op-amps may also be found in surface-mount device (SMD) packages.