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

Unconditional stability means that the operation of the amplifier is not influenced by temperature changes.

Positive feedback occurs when a portion of the output signal is fed back into the input. This portion of the wave fed back is in phase with the input, leading to an amplification effect.

Oscillator circuit.

1. The bandwidth increased, allowing for a wider range of frequencies to be amplified.
2. The level of noise (hiss) decreased, leading to a clearer output.

The ideal op amp has an output waveform that is an amplified version of the input waveform, exhibiting infinite gain.

The voltage gain (A_V) can be calculated using the formula: $A_V = -\frac{R_F}{R_{in}}$ Substituting the values: $A_V = -\frac{12000}{2200} = -5.45$

Using the voltage gain calculated earlier, the output voltage (V_out) can be computed as: $V_{out} = A_V \times V_{in}$ $V_{out} = -5.45 \times 5 = -27.25 V$.

If R_F decreases, the voltage gain of the op amp will also decrease, as it is directly proportional to the value of the feedback resistor.

The summing op-amp circuit allows for various input signals to be fed into the circuit, producing a single output signal that is the sum of all input signals.

Using the formula for output voltage in a summing amplifier: $V_{out} = -\left( V_1 + V_2 + V_3 \right)$ Substituting the values: $V_{out} = -\left( 2 + (-10) + 5 \right) = -3 V$

The circuit functions as a timing circuit.

The input trigger pulse oscillates between -V and +V, while the output corresponds to the timing defined by the trigger, typically resulting in square wave outputs.

The time delay (t) is calculated using: $t = 5 \times R \times C$ For R2 = 12 kΩ and C2 = 47 µF, $t = 5 \times 12000 \times 47 \times 10^{-6}$ which results in approximately 2.82 seconds.

The oscillating frequency (f_R) can be calculated using: $f_R = \frac{1}{2\pi \sqrt{6RC}}$ For R = 10 kΩ and C = 250 pF, this becomes: $f_R = \frac{1}{2\pi \sqrt{6 \times 10 \times 10^{-3} \times 250 \times 10^{-12}}} \approx 41.09 kHz$.

The differentiator circuit produces an output that is proportional to the rate of change of the input voltage, effectively transforming a triangular wave into a square wave.

Op-amps are typically packaged as integrated circuits within a hard plastic body, equipped with external pins for connections to other components. Additionally, they may be found in surface-mount device (SMD) configurations.