7.1 Name THREE applications of an operational amplifier (op amp) - English General - NSC Electrical Technology: Electronics - Question 7 - 2017 - Paper 1

Three characteristics of an ideal operational amplifier are:

1. Infinite input impedance: Prevents current from being drawn into the input terminals.
2. Zero voltage drop: Ensures that the voltage difference between the input terminals is effectively zero.
3. Infinite open-loop gain: Allows the amplifier to achieve very high output voltage.

Open loop refers to a configuration where there is no feedback from the output to the input of the operational amplifier. In this mode, the gain of the circuit is at its maximum, which makes the op-amp highly sensitive to any input signal, but also potentially prone to saturation.

The diagram should represent an operational amplifier configured with an inverting input, where the input voltage is applied to the inverting terminal and the non-inverting terminal is grounded. An output voltage will indicate whether the input signal exceeds a certain threshold.

Positive feedback occurs when a portion of the output signal is fed back to the input, in phase with the original input signal. This increases the gain of the system and can lead to instability, but is necessary in certain applications such as oscillators.

The very high input impedance of the operational amplifier ensures that minimal current is drawn from the preceding circuit. This means that the voltage levels will remain largely unaffected, allowing for accurate signal representation and preventing loading effects.

Three applications of RC phase shift circuits include:

1. Phase shift oscillators: Used to create sine wave signals.
2. Filters: Employed in audio circuits to manage frequency response.
3. Signal conditioning: Used in sensor applications to modify signal phase for analysis.

The input signal waveform is to be drawn, followed by the corresponding output signal which would be a scaled version of the input based on the gain of the amplifier. The output waveform should lead the input in phase.

Rf serves as the feedback resistor which connects the output to the inverting input of the operational amplifier. This feedback regulates the gain of the amplifier and determines its stability.

If the resistance of Rf is decreased, the feedback to the inverting terminal increases, reducing the overall gain of the operational amplifier. Consequently, the impact of the input signal will be less pronounced at the output.

Rin is the input resistor that establishes the input impedance of the circuit. It works in conjunction with Rf to set the gain of the amplifier circuit.

The Hartley oscillator consists of a tank circuit including an inductor and a capacitor in parallel, along with an operational amplifier. The output is taken from the amplifier which drives the oscillation.

If both signals are equal, the output of the comparator will be zero. This occurs because the comparator only amplifies the difference between the two input signals.

The frequency of the waveform remains unchanged during the amplification process, as amplification affects only the amplitude and not the frequency of the signal.

Natural oscillation frequency refers to the frequency at which an oscillator naturally oscillates without external influence. When plotted, three complete cycles of the waveform should illustrate the consistent amplitude and periodicity associated with this frequency.

Operational amplifiers are used in complex circuits to adapt and match impedance between different stages. This prevents signal loss and ensures that each stage operates within its optimal range.

A non-inverting amplifier is used when a high input impedance is required along with a specific gain. An example would be in sensor applications where the sensor’s output needs to be amplified without being loaded down.