Among the generating device it is necessary to distinguish the generators of sinusoidal (harmonious) hesitation, rectangular oscillations or signals of rectangular shape (the pulse generators) and fluctuations of the special form (for example, generators linearly varying voltage). The generator is called a self-oscillating structure, in which energy sources power is converted into electrical energy by self-oscillation. Generators of sinusoidal oscillations provide education on output devices AC (voltage) frequency. They are often used oscillatory LC-circuits (usually parallel).

Imagine a parallel LC-circuit. If the charge capacity of such a circuit to a certain voltage, then it will be stored, the corresponding energy E. Now let us close this charged capacitor to the inductance. The result will be an oscillatory exchange of energy between the capacitor and the inductor. The period of these oscillations can be defined as:

In a quarter of all the energy E will already be concentrated in the magnetic field of the inductor, and the capacitor is fully drained.. After that, the capacitor will begin to recharge the energy of the magnetic field, which in the time T/2 back to the condenser in the form of E, but the polarity of the voltage of the capacitor plates will change to the opposite. At time T the capacitor is again fully charged, and the oscillatory process will continue. Because in the real circuit there are always losses, these oscillations will die out. To prevent decay you need to apply in the contour of extra energy. Typically the replenishment of energy is provided from power source through the amplification stage.

Generators of sinusoidal oscillations usually contain an amplification cascade, covered by frequency-selective PIC, for a sustainable mode of self-excitation at a given frequency. In figure. 4.9 the flow diagram generator

sinusoidal oscillations, where K and ẋ is designated as complex quantities, what accounted for their dependence on frequency. In the future it will bear in mind, but the entry for these parameters will be done in the usual way.

For electronic devices in self-refresh mode requires two conditions. These conditions can be written in the following form:

To obtain the generator output sinusoidal voltage, it is necessary, the relationship (4.8) has been carried out only on one frequency.

The ratio (4.8and) is called the amplitude balance. The amplitude of the signal at the output of the device is in To times more, than the input. But she is weakened to x times the feedback loop. For oscillation it is necessary, to see more of the initial signal at the input of the device, t. e. To> 1/are people snacking on. This condition allows the initial changes of currents and voltages (appeared, when the device is connected to a power source) to make the necessary increase. The Condition Кϰ = 1 determines the steady-state generation mode, in which the signals at the output and input of the generator equal to their steady-state values, t. e. the gain is compensated by the feedback ratio.

The ratio (4.8b) called balance phases. Encountered on the input signal (when connecting the power source) after passing through the amplifier and feedback network must return to the input of the device without changing its phase, t. e. the total phase shift must be equal to 0, 2π, 4π and t. d. The result is the increase of the signal due to the addition of the current (or voltage) returning with the chain PIC the signal. The ratio (4.8b) obliged to provide the generator steady PIC.

Generators of sinusoidal oscillations, it is customary to distinguish the type of frequency-selective elements. So, it is possible to allocate LC-, RC and quartz (acoustoelectronic) generators.