99.2.3. Small Signal Model Description

So, the main circuit it is given here and the along with this we do have an intention to get G trans-conductance of the circuit defined by feedback network. So, if I consider this G, if we see the G in this summary table of feedback effect, what we can see here it suggests that we need to have current-series feedback or series-series feedback. And for series-series feedback, what we have the input signal, it is voltage and the output signal it is current.

In this part, we introduce the main circuit that is being analyzed. The focus is on the trans-conductance (G) of the circuit, which is influenced by the feedback network. The key takeaway is that a current-series feedback configuration is needed, where the input signal is a voltage and the output signal is a current. This distinction is important in understanding how feedback alters the circuit's behavior.

Think of a thermostat controlling a heater. Here, the thermostat receives a voltage signal from a temperature sensor (input signal) and provides a current output to adjust the heater's heat output (output signal). The feedback mechanism helps maintain the desired temperature, similar to how feedback in circuits helps achieve stable amplification.

Here we do have the model of the on a feedback circuit where we can see that at the sampling point we do have series connection and the mixing point also we do have the voltage mixing in series. And this is the primary input and the primary output here it is the current through the circuit which is we may call it is i_o.

This part describes the configuration of the feedback circuit model. It highlights the presence of sampling and mixing points, revealing how voltage inputs combine at the input node and lead to a specific current output. This current is vital since it influences the overall gain of the amplifier circuit and reflects how feedback affects performance.

Imagine a chef tasting a dish while cooking. The series connection represents the process of adding ingredients based on the primary input (initial recipe). The mixing point is where the chef combines flavors to adjust the dish, just as feedback currents adjust gains in the circuit to ensure a tasty outcome.

So, this is the v voltage we may say that this is + side and this is ‒ side. So, this v is getting mixed with v_s to produce the input voltage v_in.

Here, we discuss how the voltage across the resistor affects the overall input voltage to the amplifier. The developed voltage (v) from the feedback interacts with the primary input voltage (v_s) to contribute to the final input signal (v_in). Understanding this interaction is fundamental to grasping how feedback improves amplifier performance.

Consider filling a cup with water while monitoring the water level (v). The primary source (v_s) is the faucet, and the feedback is the water level you can see. The mixing of the water inflow and the current level helps you determine when to stop filling the cup, analogous to how voltage mixing helps optimize signal levels in a circuit.

To implement the corresponding feedback here the series-series feedback here what we have to simply do is that you have to partially bypass R_E only R_E1 will be bypassed and R_E will be working as feedback a network developing a voltage v.

This portion explains the specific configuration needed to set up the series-series feedback. It highlights that by partially bypassing one of the resistors (R_E1) while keeping another (R_E) as a feedback network, the resulting voltage (v) will improve the overall function of the circuit. This strategic use of resistors is crucial for optimizing amplifier performance.

Think of a highway with toll booths. If one lane is open without tolls (R_E1), it allows faster passage while the others (R_E) remain in use for adjustments (feedback). This arrangement ensures smooth traffic flow, similar to how the resistors help manage signal flow in the circuit for better amplification.

So, in summary we can say that G' can well approximated by g_m and R should be much less than minimum of the two; r_π and r_o.

This critical summary emphasizes the approximation of G' by trans-conductance (g_m) and the importance of selecting feedback resistor values. Keeping the feedback resistor (R) much less than intrinsic resistances helps maintain desired circuit performance and prevent loading effects. Highlighting these relationships assists in analyzing circuit behavior effectively.

Consider a water reservoir (output) connected to various pipes (inputs). If some pipes are too narrow (high resistance), water won't flow efficiently from the reservoir. To ensure proper supply, pipes need to be adequately sized (R being less than resistances), just as resistances affect signal flow in an electronic circuit.

--