The main function of a PLL is to lock on to an input logical signal of any given frequency, even when the signals are distorted, or they are coming from a noisy background, & signal is mixed with some other signals having different frequencies. The essential components of a PLL are shown in the diagram below. The first stage is the phase detector. It receives 2 logic-level signals, one at the input to the PLL and the other fed back from its output.
Read More!
Differential Amplifier
The differential amplifier (shown in fig below) is also referred to as along-tailed pair. A differential amplifier contains 2 inputs namely, vIN1 and vIN2. This amplifier is used as amplifier in order to amplify the voltage difference between its inputs. When it does this, we say that it is operating in the differential mode.
Read More!
DARLINGTON PAIR
The construction of Darlington pair consists of 2 BJTs connected as shown below in the figure. The emitter current of Q1 becomes the base current of Q2 transistor. The current gain of the pair will be equal to the product of the current gains of the individual transistors.
BYPASS CAPACITOR
The application of an emitter resistor (R4) provides improved stability but it also gives reduced gain. When needed, we can restore the gain by wiring a high-value capacitor across R4.This keeps the emitter voltage substantially constant. Without the use of capacitor, the voltage at the emitter rises and falls with the signal. And hence it will provide negative feedback.
Lets take an example, as iB rises (tending to increase vBE),iC rises, and the emitter voltage goes up. This tends to decrease vBE, which decreases iC and resists the rise in emitter voltage. Different way of analyzing this is to say that the capacitor shunts the signal at the emitter through to the ground. This is the foremost reason why C3 is called a bypass capacitor. With this capacitor inplace, the voltage gain of the amplifier is about 280.The lower cut-off point is raised to 130 Hz, so bandwidth is somewhat reduced.
FERROMAGNETISM
Ferro-magnetism is very commonly used type of magnetism. Ferromagnetism is found on the Bar magnets, compass needles, and the coating on magnetic hard disks. It is a fine property of iron, cobalt, and compounds of these few other metals which includes nickel, chromium and magnesium. All these stated materials shows ferromagnetic properties because the spins of the electrons cancel out much less than in other materials. Groups of spinning electrons align readily with an external magnetic field, thus forming magnetic domains. This alignment is permanent so that the material becomes magnetized, & remains so, even when we remove the external field.
Read More!
Permanent magnetic materials
In a permanent magnet a material is used that exhibits magnetism even in the absence of a current-carrying coil. The silicon-iron and nickel-iron alloys are ‘soft’ magnetic materials and possess high permeability & have low hysteresis loss. The converse characteristics are necessary in the ‘hard’ materials that are used for making permanent magnets. In permanent magnets, high remanent flux density & high coercive force, after magnetization to saturation, are often required for the purpose of resisting de-magnetization. The hysteresis loop should be able to embrace the maximum possible area.
Waveform harmonics
- Consider that an instantaneous voltage v be represented by the formula
v = Vm sin 2πft volts.
This is a waveform which varies sinusoidally with time t, has a frequency f, and a maximum value represented by Vm. It is normally assumed that alternating voltages have wave shapes which are sinusoidal where only 1 frequency is present. If the waveform is not happened to be sinusoidal it is called a complex wave, & whatever its shape is, itmay be split up mathematically into components called the fundamental and a number of harmonics.This process is referred to as harmonic analysis.The fundamental, which is the first harmonic, is sinusoidal and has the supply frequency, f ; the other harmonics are also sine waves having frequencies which are integer multiples of f . Thus, if supply frequency is fifty hertz, then the third harmonic frequency is 150Hz, the fifth 250Hz, & so on.
The LR–CR parallel network
A more all-purpose network containing a coil of inductance “L” and resistance RL connected in parallel with a capacitance C & resistance RC in series is presented in diagram 29.4 below.
Temperature coefficient of resistance
It is normal when the temperature of a material increases, the resistance increases in the most of conductors, insulators decrease in resistance, whilst the resistance of some special alloys remains almost constant.
The temperature coefficient of resistance of a material is the increase in the resistance of a 1OHM resistor of that material when it is subjected to a rise of temperature of 1◦C. Greek alpha is the symbol which is used for the temperature coefficient of resistance is “α”.
Thus, if some copper wire of resistance 1OHM is heated through 1◦C and its resistance is then measured as 1.0043OHM then α=0.0043Ω/Ω◦C for copper. The units are normally expressed only as ‘per ◦C’, i.e. α=0.0043/◦Cfor copper. If the 1Ω resistor of copper is heated through 100◦C then the resistance was at 100◦C would be 1+100x0.0043=1.43Ω_.
chemical effects of electricity
If we want to conduct electric current it must contain charged particles to be able to conduct electric current. In solids, the current is carried by means of electrons. Copper, lead, aluminum, iron and carbon are few common examples of solid state conductors. In liquids and gases, the part of a molecule which has acquired an electric charge is a mean of conduction electric current, called ions. These ions may possess either a positive or negative charge, and their examples include the hydrogen ion H+, copper ion Cu++ and hydroxyl ion OH−. Distilled water possesses no ions and is considered as a poor form of conductor of electricity, on the other hand salt-water contains ions and is considerably a good conductor of electricity.
Mesh-current analysis
The Mesh-current analysis is simply an extended application of Kirchhoff’s laws. Diagram 31.1 shows a network whose circulating currents I1, I2 and I3 have been allocated to closed loops in the circuit rather than to branches. Currents I1, I2 and I3 are referred to as mesh-currents or loop-currents. In mesh-current analysis the loop-currents are all arranged to circulate in the same direction (in diagram 31.1, shown as clockwise direction). Kirchhoff’s 2nd law is applied to each of the loops in turn, which in the circuit of diagram 31.1 generates 3 equations in three unknowns which may be solved for I1, I2 and I3.
