7.1 Explain what an operational amplifier (op amp) is - NSC Electrical Technology Electronics - Question 7 - 2017 - Paper 1

1. Integrated circuits are cheaper to manufacture due to mass production processes.
2. They are more versatile, allowing for compact designs and reducing the overall space required for circuit implementations.

A differential amplifier amplifies the voltage difference between two input signals. The output voltage is given by the equation:

$V_{out} = A_d (V_{in+} - V_{in-})$

where $A_d$ is the differential gain of the amplifier. It can also provide a common-mode rejection, allowing it to effectively suppress any signals that are common to both inputs.

Negative feedback is commonly used in amplifier circuits to stabilize gain and improve linearity.

Positive feedback is typically found in oscillator circuits to maintain oscillation.

Positive feedback amplifies the input signal, which can lead to increased gain but may cause instability or oscillation. Negative feedback reduces the gain and stabilizes the output, improving linearity and bandwidth.

Using the given values: $V_{in} = 0.7 ext{ V}, R_f = 170 ext{ kΩ}, R_{in} = 10 ext{ kΩ}$

The output voltage can be calculated as:

$V_{out} = V_{in} \left(1 + \frac{R_f}{R_{in}}\right) = 0.7 V \left(1 + \frac{170}{10}\right) \approx 12.6 V$

The voltage gain $A_v$ is calculated using:

$A_v = -\frac{R_f}{R_{in}} = -\frac{170,000}{10,000} = -17$

An inverting operational amplifier produces an output that is 180 degrees out of phase with the input signal. It inverts the input signal and provides a proportional output based on the ratio of the feedback resistor to the input resistor.

One application of a monostable multivibrator is used in timer circuits where a single pulse is generated in response to an input trigger.

A monostable multivibrator has one stable state and converts a trigger pulse into a single output pulse, while a bi-stable multivibrator has two stable states and can maintain its state until a trigger pulse changes it.

The integrator op amp takes a step input signal and produces a ramp output. This can be represented graphically with the input waveform being stepped and the output showing a continuous ramp.

For the inverting comparator, the output remains at one stable state until the input crosses the reference voltage, resulting in a square wave output.

The Schmitt trigger applies hysteresis to provide noise margins. The output switches states based on the upper and lower trigger levels of the input signal.

The summing op amp output will be a weighted sum of the input waveforms, where each input is inverted and summed to produce a single output waveform.

Using: $V_{out} = -\frac{R_f}{R_{in}} \cdot V_{in} = -\frac{200k}{20k} \cdot 5V = -50V$

The gain is calculated in the same manner as the output voltage: $A_v = -\frac{R_f}{R_{in}} = -10$

A Schmidt trigger is often used in signal conditioning to eliminate noise from a signal and to create clean digital transitions.

The resonant frequency $f$ is given by: $f = \frac{1}{2\pi\sqrt{LC}}$ For $L = 27 \text{ mH}$ and $C = 47 \mu F$, substituting values we find: $f = \frac{1}{2\pi\sqrt{(27 \times 10^{-3})(47 \times 10^{-6})}} \approx 141.28 Hz$

The frequency $f$ of the oscillator can be calculated by the formula: $f = \frac{1}{2\pi RC}$ For resistors $R = 25k\Omega$ and capacitors $C = 45 pF$, the total frequency can be computed as: $f = \frac{1}{2\pi (25 \times 10^{3})(45 \times 10^{-12})} \approx 57.76 kHz$