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

Unconditional stability refers to the characteristic of an op amp where its operation remains stable regardless of variations in temperature or component values. This ensures that the amplifier can maintain a consistent performance and output without the risk of oscillation or instability under varying conditions.

Positive feedback occurs when a portion of an amplifier's output is fed back into the input in phase with the original input signal. This can lead to an increase in the amplitude of the output signal, and when used correctly, it can cause the circuit to oscillate or amplify a signal more significantly.

An oscillator circuit utilizes positive feedback to generate continuous waveforms.

1. Reduced Distortion: Negative feedback helps to lower the distortion in the output signal, providing a clearer and more accurate amplification of the desired signal.
2. Improved Stability: Negative feedback enhances the stability of the amplifier by making its gain less sensitive to variations in temperature and other external factors.

The output of an ideal op amp can be expressed as:

• If the input voltage is greater than the reference voltage, the output will saturate to the positive supply voltage.
• If the input voltage is less than the reference voltage, the output will saturate to the negative supply voltage. Insert drawn output graph based on the given input signal.

To calculate the voltage gain (A_V), we use the formula:

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

Substituting the values:

• $R_F = 12,000 \Omega$
• $R_{in} = 2,200 \Omega$

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

Using the voltage gain calculated previously:

• Input signal $V_{in} = 5 V$
• Output voltage $V_{out} = A_V \times V_{in}$

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

If $R_F$ decreases, the voltage gain of the op amp will also decrease, as the voltage gain is directly proportional to the feedback resistance. This may lead to a lower amplification of the input signal.

The summing op-amp circuit allows for multiple input signals to be summed and processed simultaneously. It effectively combines the weighted inputs into a single output signal, which is the algebraic sum of the input voltages.

Using the given input voltages: $V_{out} = -(V_1 + V_2 + V_3)$ Substituting the values:

• $V_1 = 2 V$
• $V_2 = -10 V$
• $V_3 = 5 V$

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

The function of the monostable multivibrator circuit is to produce a single output pulse of a specific duration in response to a trigger pulse. This allows for the generation of precise timing events in digital circuits.

Insert drawing showing the relationship between the trigger pulse and the output pulse, with properly labeled time intervals (T1, T2, etc.).

The time delay (t) in a monostable multivibrator can be calculated using the formula:

$t = 1.1 \times R \times C$

Substituting the values:

• $R = 12,000 \Omega$
• $C = 47 \times 10^{-6} F$

$t = 1.1 \times 12000 \times 47 \times 10^{-6} = 0.282 s$

The oscillating frequency ($f_R$) can be calculated with:

$f_R = \frac{1}{2\pi R C}$

Using the values:

• $R = 10,000 \Omega$
• $C = 250 \times 10^{-12} F$

$f_R = \frac{1}{2\pi \times 10,000 \times 250 \times 10^{-12}} \approx 41.09 Hz$

In a differentiator circuit, the op amp produces an output that is proportional to the rate of change of the input signal. The output voltage reflects the derivative of the input voltage over time, effectively turning a square wave input into a triangular output, reflecting the input signal's changes.

Op amps are typically packaged as integrated circuits within a hard plastic body that features external pins for connecting to circuits. Additionally, they may come in surface mount devices (SMD) for modern PCB designs, offering compact solutions for circuit integrations.