Initial phase condition: phase balance.

Conditions for maintaining oscillation: |AF|= 1

Sine wave oscillators can be divided into two categories: one is a feedback oscillator based on feedback principle, which is the most widely used oscillator at present; The other is the negative resistance oscillator, which directly connects the negative impedance element to the resonant circuit, and uses the negative impedance effect of the negative impedance element to cancel the loss in the circuit, thus generating sine wave oscillation.

Extended data:

In order to make the output amplitude increase continuously in the process of oscillation, the feedback signal should be larger than the signal input to the amplifier, that is, the oscillation should start with amplitude oscillation, that is, t (j ω) >: 1 is called the starting condition of self-excited oscillation.

Corresponding to the equilibrium condition, the initial condition of the oscillator can be subdivided into the initial amplitude condition (| t (j ω) | >; 1) and the phase condition (ψ (t) =ψ (k) +ψ (f) +ψ (f') = 2nπ, n = 0, 1, 2 ...), in which the phase condition of oscillation is a positive feedback condition.

According to the nature of the resonant circuit, the circuit should be purely resistive at resonance, so the three reactive elements cannot have the same properties. Generally speaking, the loop q value is very high, so the loop current is much larger than the base current of the transistor? B, collector current? C and emitter current? e .

Sine wave oscillator can be used as a part of the equipment, or it can be made into a separate equipment. In communication equipment, if the carrier frequency and local oscillation frequency are above several hundred kilohertz, LC sine wave oscillator is generally used. The working frequency of negative resistance LC sine wave oscillator is above 100MHz. When high frequency stability is required, a quartz crystal oscillator is used.

Various sound alarms, vibration signals in telephone communication equipment, dial tone, busy tone, etc. The oscillation frequency is in a considerable range, and RC sine wave oscillator is used. The sine wave signal source for testing requires adjustable amplitude and frequency, and has certain load capacity. As a signal source, this kind of tester mainly consists of oscillator, amplifier, attenuator and other auxiliary circuits.

High frequency furnace with high frequency and high power does not require high frequency stability. Usually, a high-power electron tube is connected to form an oscillation circuit, and the energy is directly obtained from the electromagnetic field in the inductance coil of the oscillation circuit.

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