Electronic Circuits and Diagram-Electronics Projects and Design

INTRODUCTION Almost all electronic devices used in electronic circuits need a dc source of power to operate. The source of dc power is used to establish the dc operating points (Q-points) for the passive and active electronic devices incorporated in the system. The dc power supply is typically connected to each and every stage in an electronic system. It means that the single requirement common to all phases of electronics is the need for a supply of dc power. For portable low-power systems batteries may be used, but their operating period is limited. Thus for long time operation frequent recharging…

PLL Application – FSK (Frequency Shift Keying) Demodulator FSK demodulator  using NE-SE 565 IC A very useful application of the 565 PLL is as a FSK demodulator. In the 565 PLL the frequency shift is usually accomplished by driving a VCO with the binary data signal so that the two resulting frequencies corre­spond to the logic 0 and logic 1 states of the binary data signal. The frequencies corresponding to logic 1 and logic 0 states are commonly called the mark and space frequencies. Several standards are used to set the mark and space frequencies. An FSK signal demodulator can…

PLL Application – Frequency Demodulation Using NE-SE 565 IC Frequency demodulation or detection can be obtained directly by using the PLL circuit. When the centre frequency of the PLL is selected or designed at the FM carrier frequency, the filtered or output voltage in the circuit shown in figure, is obviously the desired demodulated voltage, that varies in magnitude in proportion to the signal frequency. The PLL circuit thus can be operated as complete IF strip, limiter, and detector as employed in FM receivers. The 565, very popular PLL unit, containing a phase comparator PC, amplifier, and VCO, is shown in…

PLL Applications 1. Frequency Multiplication or Frequency Synthesis The block diagram of a frequency muliplier (or synthesizer) is shown in figure. In this circuit, a frequency divider is inserted between the output of the VCO and the phase comparator (PC) so that the loop signal to the PC is at frequency fOUT while the output of VCO is N fOUT. This output is a multiple of the input frequency as long as the loop is in lock. The desired amount of multiplication can be obtained by selecting a proper divide- by N network where N is an integer. Figure shows…

How a PLL works ? Consider VCO operating without input signal at free-running frequency fr and input signal of frequency fIN increasing from zero is applied to the PC. If the input frequency is less than fIN1, then the error voltage Ve is zero as illustrated in figure and VCO operates at a frequency fr. When the input signal frequency fIN reaches a frequency fin1 (the lower edge of the capture range), then the output or error voltage Ve jumps from zero to some negative voltage with beat notes of frequency (difference between input signal frequency and actual VCO output…

Operating principle of Phase Locked Loops The block diagram showing operating principle of PLL is given in figure. As illustrated in this fig, the PLL consists of a phase detector, a low-pass filter and a voltage controlled oscillator. Phase Detector A phase detector is basically a comparator that compares the input frequency fin with feedback frequency fout. The phase detector receives two digital signals, one from the input, the other feedback from the output. The loop is locked when these two signals are of the same frequency and have a fixed phase difference (A locked PLL is analogous to an…

Introduction to PLL or Phase Locked Loops Phase-locked loop is a feedback loop consisting of a phase detector, a low-pass filter, amplifier (optional) and a voltage-controlled oscillator (VCO), as illustrated in figure. It plays the same role in the frequency or phase world as the op-amp does in the voltage world. The op-amp has two voltage inputs, non-inverting and inverting (normally used for feedback from the output). Similarly, the PLL has two inputs; the PLL’s feedback input is normally connected to the circuits’ output. Digital frequencies are usually applied. The op-amp changes its output voltage to whatever values is necessary…

Introduction to Operational Amplifiers An operational amplifier, abbreviated as op-amp, is basically a multi-stage, very high gain (typically 2,00,000), direct-coupled, negative feedback amplifier that uses voltage-shunt feedback to provide a stabilized voltage gain. An op-amp has high input impedance (ex­ceeding 100 kilo Ohms) and low output impedance (less than 100 Ohms) and has capability of ampli­fying signals having frequency ranging from zero Hz to 1 MHz, that is, op-amp can be used to amplify dc as well as ac input signals. Although discrete op-amps are built, designers of industrial electronic circuit now use integrated circuit operational amplifiers (IC op-amps) almost…

The programmable unijunction transistor (PUT) is not a unijunction transistor at all. The fact that the V-I characteristics and applications of both are similar prompted the choice of labels. It is also a four-layer P-N-P-N solid-state device with a gate connected directly to the sandwiched N-type layer. The basic structure, schematic symbol and the basic biasing arrangement of PUT are shown in figures respectively. As the symbol indicates, it is essentially an SCR with a control mechanism that permits a duplication of the characteristics of the typical SCR. The term “programmable” is applied because the inter base resistance RBB, the…

The relaxation oscillator shown in figure consists of UJT and a capacitor C which is charged through resistor RE when inter base voltage VBB is switched on. During the charging period, the voltage across the capacitor increases exponentially until it attains the peak point voltage VP. When the capacitor voltage attains voltage VP, the UJT switches on and the capacitor C rapidly discharges through B1. The resulting current through the external resistor R develops a voltage spike, as illustrated in figure and the capacitor voltage drops to the value VV. The device then cuts off and the capacitor commences charging…