4.1. Analog Electronic Circuits

Welcome to again the second part of this topic namely Revisit of this some of the Prerequisite. In fact, prerequisite part we already have completed, but under this one we are about to start some topic called non-linear; analysis of non-linear circuit.

In this section, the speaker introduces the focus on non-linear circuit analysis, indicating that this is a continuation or a revisit of previously covered prerequisites. Non-linear circuits are characterized by their non-linear relationships between voltage and current, making their analysis distinct from linear circuits.

You can think of non-linear circuits like a car accelerates—it doesn’t go from 0 to 60 mph at a constant pace; it speeds up more rapidly at lower speeds compared to when it approaches its maximum speed. This non-linear behavior is similar to how non-linear circuits don't behave in a simple predictable manner.

Now, we are going to talk about analysis of non-linear circuit and the corresponding approximation. We are considering a simple diode circuit as shown here. It consists of the input voltage V which is applied to a series connection of a resister R and a diode.

Here, the speaker sets the stage for analyzing a simple diode circuit, which includes a diode and a resistor. The diode's characteristics are significant as they are non-linear; the analysis must consider how both the resistor and diode interact with the input voltage (V).

Imagine a water flow system where a valve (representing the diode) controls how quickly water (current) flows based on the pressure (voltage). The relationship is not straightforward—more pressure doesn't always lead to more water flow, similar to the non-linear characteristics of a diode.

Now, as you know that this diode I-V characteristic it is non-linear. So, we know that the current flowing through a diode I, it is a strong function of the voltage across this diode V. To be more precise, it is exponential.

Diodes exhibit a non-linear current-voltage (I-V) characteristic where the current flowing through the diode changes exponentially with the applied voltage. This means that small changes in voltage can lead to significant changes in current, highlighting the non-linear nature.

Think of a light dimmer switch that doesn't just turn the light on or off, but adjusts the brightness in a gradual way—similar to how diodes allow current to flow in response to exponentially increasing voltage, rather than a direct linear response.

So, you may be aware that this I reverse saturation current its value it is in the order of 10‒10 mA. So, it is very small current and then it is slightly higher than 1 maybe 1.5 or sometimes 2 but for our discussion this is approximately 1.

The speaker describes the reverse saturation current, which is a minimal current that flows through a diode when it is reverse-biased. This detail is crucial for understanding diode behavior, especially in small signal analysis and circuit design.

Imagine a tiny leak in a dam. Even though it's a small amount of water trickling through (similar to the reverse saturation current), it can still be significant for understanding how the dam operates overall.

We can split this characteristic curve into two parts; one is when V < V_γ the diode is OFF, the other one it is when V > V_γ so we can say then the diode it is ON.

The speaker explains that the I-V characteristics of a diode can be simplified into two regions: the 'OFF' region when the voltage is below a certain threshold (V_γ) and the 'ON' region when above that threshold. In these two regions, different approximations can be made for analysis.

Consider a light switch: when the switch is off, no current flows to the light (OFF), and when the switch is on, the light illuminates brightly (ON). This analogy helps illustrate how diodes operate in either an active or inactive state based on the applied voltage.

In this approximated straight line what we can say that this I ≈; here r is ON resistance of the diode. In fact, this r is reciprocal of this slope.

In the ON condition, the diode's behavior can be approximated as a linear relationship, simplifying the analysis. The slope of this relation is determined by the diode's ON resistance, which is the reciprocal of this slope. This allows for straightforward calculations in circuit analysis.

You can think of this as if you were measuring the steepness of a hill. The steeper the hill (higher slope), the more difficult it is to climb, just like a higher ON resistance makes it harder for current to flow through the diode.

So, whenever in a non-linear circuit we are feeding the signal then what may be the situation? So, we have the resistor, we have the diode and then we do have DC, maybe this is a DC and then in case if you have a signal coming in series with this DC.

The speaker discusses the scenario where both direct current (DC) and an alternating current (AC) signal are applied to the circuit. This complex dynamic adds another layer of analysis as the diode will respond differently depending on the superimposed signals.

Think of combining a steady stream of water (DC) with occasional waves (AC) in a river. The river’s flow will be influenced by both the continuous water flow and the changing waves, representing how AC signals affect the overall behavior of a circuit with a DC bias.

Most of the cases we may ignore, we may keep the focus only on signal we may ignore this DC part. But here with this example I am trying to explain that you should not be completely ignoring this DC part because that really defines the input to output transfer characteristic.

The speaker emphasizes the importance of the DC level within a non-linear circuit. Ignoring the DC component can lead to inaccuracies in predicting how the circuit will respond to input signals—this level helps define how the circuit behaves overall.

When cooking, the base ingredients (like a broth) create the foundation for flavors. Ignoring the broth (DC level) while only focusing on spices (AC signals) may lead to a poorly balanced dish, similar to missing key elements in circuit analysis.

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