Electronic Circuits and Diagram-Electronics Projects and Design

In crystal oscillators, the usual electrical resonant circuit is replaced by a mechanically vi­brating crystal. The crystal (usually quartz) has a high degree of stability in holding con­stant at whatever frequency the crystal is originally cut to operate. The crystal oscillators are, therefore, used whenever great stability is needed, for example, in communication trans­mitters, and receivers, digital clocks etc. A quartz crystal exhibits a very important property known as piezo-electric effect. When a mechanical pressure is applied across the faces of the crystal, a voltage proportional to the applied mechanical pressure appears across the crystal. Conversely, when a voltage is applied across the…

The Hartley oscillator is as popular as Colpitt’s os­cillator and is widely used as local oscillator in radio receivers. The circuit arrangement is shown in figure. Hartley oscillator circuit is similar to Colpitt’s oscillator circuit, except that phase-shift network consists of two inductors Lr and L2 and a capacitor C instead of two capacitors and one inductor. The output of the amplifier is applied across inductor Lx and the voltage across inductor L2 forms the feedback voltage. The coil L1 is inductively cou­pled to coil L2, the combination functions as an auto-transformer. However, because of direct connec­tion, the junction of…

  The Clapp oscillator shown in figure. is a refinement of the Colpitt’s oscillator. The single inductor found in the Colpitt’s oscillator is replaced by a series L-C combination. Addition of capacitor Ca in series with L improves the frequency stability and eliminates the effect of transistor parameters on the operation of the circuit. The op­eration of the circuit is the same as that of the Colpitt’s oscillator. As the circulating tank current flows through C1, C2 and C3 in series, the equivalent capacitance is C = C1C2C3/C1C2 + C2C3 + C1C3 The frequency of oscillation is given as Capacitors C1 and…

  The Colpitt’s oscillator circuit is a superb circuit and is widely used in commercial signal generators upto 100 MHz. The basic circuit of a Colpitt’s oscillator is shown in figure. It basically consists of a single stage inverting amplifier and an L-C phase shift network, as obvious from the circuit diagram shown. The two series capacitors Ct and C2 form the potential divider used for providing the feedback voltage – the voltage developed across capacitor C2 provides the regenerative feedback required for sustained oscillations. Parallel combination of RE and CE along with resistors Rj and R2 provides the stabilized…

When a parallel tuned L-C circuit is placed in the base-to-ground circuit, the oscillator is known as the tuned-base oscillator. The basic circuit of a tuned-base oscillator is shown in figure. The circuit is also named as the tickler oscillator or Armstrong oscillator (named after its inventor). The dc bias is determined by the resistors R1, R2 and RE. The parallel RE – CE network in the emitter circuit is a stabilizing circuit and prevents the degeneration of the signal. As usual, Cc is the dc blocking capacitor. Lx and L are the primary and secondary mutually coupled coils of an…

The basic circuit of a tuned collector oscillator is shown in figure. It is called the tuned-collector oscilla­tor, because the tuned circuit is connected to the collector. The tuned circuit, constituted by the capacitor C and transformer primary coiL, forms the load impedance and determines the frequency of oscillation. The resistors R1 R2 and RE form the dc biasing circuit of the transistor. Capacitors C1 and CE are bypass capacitors for R9 and RE respectively so that the ac operation of the circuit is not affected. Moreover, C1 provides ac ground for the transformer secondary. The output voltage developed across…

What are LC Oscillators and its types ? Oscillators, which use inductance-capacitance (L-C) circuits as their tank or oscillatory cir­cuits are called L-C oscillators. L-C oscillators are very popular for generating high-frequency outputs (e.g. 10 kHz to 100 MHz). There is a large variety of L-C oscillators such as Tuned-collector oscillators, Tuned-base oscillators, Colpitt’s oscillators, Hartley oscillators, Clapp os­cillators, crystal oscillators

Essentials of Transistor Oscillators An oscillator must have the following three elements Oscillatory circuit or element. Amplifier. Feedback network. The oscillatory circuit or element, also called the tank circuit, consists of an inductive coil of inductance L connected in parallel with a capacitor of capacitance C. The frequency of oscillation in the circuit depends upon the values of L and C. The actual frequency of oscillation is the resonant or natural frequency and is given by the expression f = 1 / 2∏√LC Hz , where L is inductance of coil in henrys, and C is the capacitance of capacitor in…

How an oscillator operates ? Related Articles BASIC OSCILLATORY CIRCUITS TRANSISTOR PHASE SHIFT OSCILLATOR NEGATIVE RESISTANCE OSCILLATORS HARTLEY OSCILLATOR To know the basics of oscillators, its frequency stability, types of oscillations, different types of oscillators and so on, use the tag link – OSCILLATORS A feedback amplifier having closed-loop gain, Af greater than unity can be obtained by the use of a positive feedback. This result also satisfies the phase condition and thus results in the operation of an oscillator circuit. An oscillator circuit then provides a constantly varying output signal. If the out­put signal varies sinusoidally, the circuit can…

Related Posts OSCILLATOR OPERATION BASIC OSCILLATORY CIRCUITS CLAPP OSCILLATOR WIEN BRIDGE BRIDGE OSCILLATOR LC OSCILLATORS AND TYPES Even if an oscillator is set at an initial frequency, it cannot be maintained throughout. They keep on changing either in a uniform way or sometimes erratically.  the term “frequency stability” is used to define the ability of the oscillator to maintain a single fixed frequency as long as possible over a time interval. These deviations in frequency are caused due to variations in the values of circuit features (circuit components, transistor parameters, supply voltages, stray-capacitances, output load etc.) that determine the oscillator…