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Multivibrator - Phase shift oscillator - Bias oscillator - Output generating circuits
.. Electronics

Multivibrator

The "multivibrator" is characterized by producing a wide range of frequency output that suits the required operating conditions and uses two valves or transistors (226), the first transistor A includes a collector resistance M1 and a base resistance M2, and the second B includes resistors M3 and M4. In addition, the capacitor S A connects the collector of transistor A with the base of transistor B while the capacitor S? connects the collector of B with the base of A. Thus, each transistor pushes the other and the value of the fundamental frequency in the circuit becomes subject to the values ​​of the resistors and capacitors present.

Phase shift oscillator

It is known that moving the base voltage of the transistor in the positive direction leads to a decrease in the collector current intensity and that reducing the current intensity passing through the collector resistance leads to a decrease in its voltage and thus to moving the collector voltage in the negative direction. The result is that the feedback phase between the collector and the base becomes unsuitable for maintaining permanent oscillations, i.e. the phase is positive when it should be negative and vice versa. To avoid this error, two transistors should be used, each of which reverses the phase of the other (226).

As for the circuit that includes one transistor or one valve, a way must be found to reverse the phase so that the feedback can maintain the oscillations. One of these methods is the method that uses resistors and capacitors that form a phase shift circuit (227).

Biased oscillator

It is noted in Figure (228) that obtaining the oscillations is done by making the appropriate connection of the primary coils N and the secondary coils N of the oscillator coil. For example, reversing the connection in the secondary coil leads to reversing the phase of the feedback towards the base. The value of the oscillations also depends on the value of both the coils and the capacitor SA, and an interconnection point can be placed in the primary to match the load of the transistor collector. The output is taken from another interconnection through the capacitor S2 to provide the recording process with a high-frequency bias.

Electronic clock

Figure (229) shows a circuit for producing slow-speed pulses with extreme precision and timing. It is worth noting that the piezoelectric blouse oscillator operates at a specific frequency that is determined in advance, and can be reduced by the known division circuits to obtain slow-speed pulses used in the timing process. In this case, the crystal is responsible for adjusting this device.

226 - Multi-oscillator with two transistors.
227 - Oscillator with a shift network.
228 - High-frequency tape recorder bias oscillator.
229 - Electronic clock.