Revision: Electronics and Communication Physics HSC Science Class 12 Tamil Nadu Board of Secondary Education

The reverse voltage at which the current suddenly increases rapidly is called the breakdown voltage.

The ratio of voltage to current at any operating point of a diode is called static resistance.

The ratio of a small change in voltage to the corresponding small change in current is called dynamic resistance.

The boundary formed when p-type and n-type semiconductor regions are joined in a single crystal is called a p-n junction.

The region around the junction that is free from mobile charge carriers is called the depletion region.

The potential difference developed across the depletion layer due to immobile ions is called the barrier potential.

The two-terminal semiconductor device that allows current mainly in one direction is called a p-n junction diode.

The process in which charge carriers move from a higher concentration to a lower concentration is called diffusion.

The motion of charge carriers under the influence of an electric field is called drift.

The minimum forward voltage after which the current rises sharply is called the knee voltage.

The small current flowing in reverse bias due to minority carriers is called the reverse saturation current.

The dc common-base current ratio or current gain (α_dc) is defined as the ratio of the collector current (I_c) to emitter current. (I_g)

`alpha_"dc" = "I"_"C"/"I"_"E"`

The maximum value of an alternating current or emf in either direction is known as the peak value.

The dc common-emitter current ratio or current gain (β_dc) is defined as the ratio of the collector current (I_C) to base current (I_B).

`beta_"dc" = "I"_"C"/"I"_"B"`

A junction transistor which is a semiconductor device having two junctions and three terminals, in which the current is carried by both electrons and holes (hence the name Bipolar), is called a Bipolar Junction Transistor.

A transistor configuration in which the collector of the transistor is common to both the input and the output is called the Common Collector (CC) Configuration.

A transistor configuration in which the emitter of the transistor is common to both the input and the output is called the Common Emitter (CE) Configuration.

A transistor configuration in which the base of the transistor is common to both the input and the output is called the Common Base (CB) Configuration.

A transistor in which a p-type semiconductor (base) layer separates two layers of the n-type semiconductor (emitter and collector), and in whose circuit symbol the arrow is drawn from base pointing towards emitter, is called an n-p-n Transistor.

A transistor in which an n-type semiconductor (base) layer separates two layers of the p-type semiconductor (emitter and collector), and in whose circuit symbol the arrow is drawn from emitter pointing towards base, is called a p-n-p Transistor.

The range of frequencies required to transmit a piece of specified information in a particular channel is called channel bandwidth or the bandwidth of the transmission system.

R = \[\frac {V}{I}\]

\[r_d=\frac{\Delta V}{\Delta I}\]

\[\alpha_{ac} = \dfrac{\Delta I_C}{\Delta I_E}\]

α_dc ​= \[\frac {I_C}{I_E}\]​ (value lies between 0.95 to 0.99)

\[\beta_{ac} = \dfrac{\Delta I_C}{\Delta I_B}\]

β_dc ​= \[\frac {I_C}{​I_B}\]​​ (always > 1)

• A p-n junction is formed by joining p-type and n-type semiconductor regions in a single crystal.
• Diffusion of carriers creates a depletion region and barrier potential.
• A p-n junction diode conducts mainly in one direction.
• In forward bias, the barrier potential decreases, and the current becomes large.
• In reverse bias, the barrier potential increases and only a small minority-carrier current flows.
• In zero bias, the diffusion and drift currents balance, so the net current is zero.
• The knee voltage is about 0.3 V for germanium and 0.7 V for silicon.
• Static resistance is given by R = V/I, and dynamic resistance is given by r_d = ΔV/ΔI.

1. For a transistor operating as an amplifier in CE configuration, the E-B junction is forward biased while the C-B junction is reverse biased.
2. The AC current gain (βac) is the ratio of small change in collector current (ΔI_C) to small change in base current (ΔI_B) at constant V_CE. The DC current gain (βdc) is the ratio of I_C to I_B, which is always greater than 1.
3. The Voltage Gain (A_v) is the ratio of change in output voltage (ΔV_o) to change in input voltage (ΔV_i). The Power Gain is the ratio of change in output power (ΔP_o) to change in input power (ΔP_i).
4. In output characteristics, I_C is independent of V_CE as long as the collector-emitter junction is reverse biased. I_C is large for large values of I_B when V_CE is constant.