Analogue Electronics II - Lecture 5

Biasing refers to the establishment of suitable DC values of different currents and voltages of a given transistor.

The goal of amplification is to increase the amplitude of an AC signal without distortion or clipping the waveform.

The selection of a proper DC operating point or quiescent point generally depends on the amplitude of the AC signal to be handled and the load to which the amplifier is to work for a corresponding supply voltage.

<p>The load line drawn on the output characteristic curves determines the quiescent point (Q-point), ensuring that the transistor operates in the active region between saturation and cutoff.</p> Signup and view all the answers

<p>The best Q-point for a linear amplifier is midway between saturation and cutoff.</p> Signup and view all the answers

<p>False (B)</p> Signup and view all the answers

<p>The DC current gain (βdc) is dependent on the operating point (Q-point) and temperature.</p> Signup and view all the answers

<p>The DC operating point of a transistor amplifier shifts mainly due to changes in temperature because the transistor parameters, such as β, Ico, and VBE, are functions of temperature.</p> Signup and view all the answers

<p>Voltage-Divider-Biased (B)</p> Signup and view all the answers

<p>The most widely used type of transistor biasing circuit is the voltage-divider biasing circuit.</p> Signup and view all the answers

<p>False (B)</p> Signup and view all the answers

<p>The advantage of voltage-divider bias is that it is more stable, meaning it is less dependent on the current gain (β) of the transistor, making it a more reliable biasing method.</p> Signup and view all the answers

<p>The emitter-bias circuit is independent of β making it as stable as the voltage-divider type.</p> Signup and view all the answers

<p>The drawback of the emitter-bias circuit is that it requires two power supplies.</p> Signup and view all the answers

<p>These two key equations help analyze the emitter bias circuit by providing the base current (IB) and the collector current (IC) values, which are essential for understanding the overall circuit behavior.</p> Signup and view all the answers

<p>The most important advantages of using the voltage-divider bias circuit are its stability and good performance in linear amplifier applications.</p> Signup and view all the answers

<p>Emitter-biased transistor circuits are independent of β because the emitter current (IE) is directly proportional to the voltage across the emitter resistor (RE). As a result, the base current (IB) is determined primarily by RE and is not heavily influenced by β.</p> Signup and view all the answers

<p>It is considered &quot;Universal Bias&quot; because of its ability to provide a stable operating point for a wide range of transistors and operating conditions.</p> Signup and view all the answers

<p>It requires a dual-polarity power supply. (D)</p> Signup and view all the answers

<p>Key characteristics of a voltage-divider bias circuit include its use of a voltage divider network to establish the base voltage, its stability against changes in hFE, and its suitability for linear amplifier applications.</p> Signup and view all the answers

<p>The key characteristics of the emitter-bias circuit are its use of a split power supply, its independence from changes in hFE, and its suitability for linear amplifier applications.</p> Signup and view all the answers

<p>The most commonly used transistor biasing circuits include the voltage-divider bias, the emitter-bias, and the fixed-bias circuits.</p> Signup and view all the answers

<p>The main difference is that in a fixed-bias circuit, the base current is directly determined by the base resistor (RB), which is fixed. In a voltage-divider bias circuit, the base voltage is determined by a voltage divider network consisting of resistors R1 and R2, providing more stability.</p> Signup and view all the answers

<p>The emitter resistor (RE) is used to improve the stability of the circuit by reducing the influence of variations in the current gain (β). The RE provides negative feedback to the base of the transistor, ensuring that the operating point remains stable.</p> Signup and view all the answers

A process of setting up appropriate DC values for currents and voltages in a transistor.

The DC operating point of a transistor amplifier, determined by the intersection of the load line and the transistor characteristic curve.

The goal is to ensure the Q-point remains in the active region, avoiding saturation or cutoff where the signal gets distorted or clipped.

The amplitude of the AC signal to be amplified and the maximum distortion level allowed.

The load connected to the output of the amplifier and the corresponding supply voltage.

The transistor operates as an amplifier only when the B-E junction is forward biased and the B-C junction is reverse biased.

A graphical representation that shows the relationship between the collector current (IC) and the collector-emitter voltage (VCE) for a transistor.

A straight line on the output characteristic that represents the relationship between VCE and IC for a specific load resistor.

A biasing method where the base current is directly controlled by a resistor connected to the base.

It's highly dependent on the value of β, which can vary considerably between transistors and with temperature.

An emitter resistor (RE) is added to the circuit to improve stability by minimizing the effects of β variations and temperature changes.

A biasing method that uses a voltage divider to establish a stable base voltage, making it less susceptible to changes in β and temperature.

It requires a larger current flowing through the divider resistors than through the base, ensuring that changes in base current have a minimal effect on the base voltage.

A biasing method that uses two power supplies (one positive and one negative) to establish a stable Q-point, with less dependence on β.

A specific case of emitter-bias where the base resistor is grounded, making the circuit independent of β and temperature changes.

One way to improve the stability of a transistor circuit is to connect a resistor between the collector and the base.

This configuration provides negative feedback, meaning any change in collector current tends to reduce the base current, stabilizing the Q-point.

It uses a resistor connected between the emitter and the base, providing feedback, making the circuit less dependent on β.

The transistor operates primarily as an amplifier, amplifying AC signals applied to the input.

The transistor is in the active region when the base-emitter junction is forward biased and the base-collector junction is reverse biased.

The DC current gain (βdc) is not constant and depends on factors like the operating point and temperature.

High βdc values mean a small base current can control a large collector current, while low βdc values mean a larger base current is needed.

To ensure the stability of the Q-point, the value of R2 (the resistor connected to the base in a voltage-divider bias circuit) should be significantly smaller than the β multiplied by the emitter resistor (RE).

A biasing method that aims to establish a stable Q-point by using a combination of resistors and a voltage source to provide a stable reference voltage for the base, providing a stable base current.

A common type of feedback bias where the collector current is feedback to the base, reducing the base current if the collector current increases and vice-versa, thus stabilizing the operating point.

A biasing method that uses a resistor connected between the emitter and base, creating a feedback loop.

It's crucial to design biasing circuits in a way that minimizes the effects of variations in β and temperature on the Q-point, ensuring the transistor operates consistently and effectively as an amplifier.

They are often chosen for their ability to provide relatively stable operation over a range of conditions, making them suitable for various amplifier applications.