Question

Microelectronic Circuits 7e Chapter 4 test, Diodes. Can anyone please give me all necessary formulas

the test is over Diodes and i was just asking for any useful formulas revolving around Diodes and when to use them

Answer 1

DIODES

Definition : Diode is electronic component which has two terminals. It conducts current in only one direction hence it is unidirectional device.

diode works in three regions

1. Forward bias region when V>0

2.Reverse bias region when V<0

3.Breakdown region when V< -V _ZR

According to the V-I characteristics of diode

When the voltage is positive the diode is in forward region

therefore the ideal diode equation is approximatesas

Where  

I_s = constant for a given diode at given temperature

k = Boltzmann's constant = 1.38 x 10^-23 joules/kelvin

T- the absolute temperature in kelvins = 273 + temperature in °C

q = the magnitude of electronic charge = 1.60 x 10^-19 coulomb

This equation is used whenever you are asked to calculate ideal diode current or you are asked to find out ideal diode equation

Whenever the diode voltage is negative then it is operating in reverse region and in that case

i = - I_s

Exponential model of diode

Most accurate operation of diode in the forward region can be obtained by exponential model

Let us assume V_DD >0.5 V therefor I_D will be much greater than I_s

In this case

apply kirchhoff's law to the given circuit

other equation for caluclation I_D is written as

This formula is used when you are given with the circuit having diode

Precise Linear model (battery + resistance)

In this case

If V_D < = V _{D 0}

then I_D= 0

if V_D > = V _{D 0}

I_D = (V_D - V _DD) / r_D

Constant voltage drop model

For I_D > 0

V_D = 0.7 V

Small signal model

I_D = V_D/ r _D

r _D = n V_T / I_D

Operation of diode

P-n Junction diode

n = p = n _i

n _i = concentration of free electrons or holes in intrinsic silicon at a given temperature.

B = 5.4 x 10 3 1 for silicon,

E _G =1.1 2 electron volts (e V) for silicon,

and k = Boltzmann's constant = 8.62 x 10 - 5 e V/K

At (T ~ 300 K), n _i = 1.5 x 10¹⁰ carriers/cm ³

j _p is the current density

D_p = Constant = current density

Built in voltage

N_A and N_D are the doping concentrations of the p side and n side of the junction,

Width of depletion region

= 11.7

= 1.04 x 10 ^-12 F/cm

Junction Capacitance or depletion capacitance