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The implementation of the phase-shift oscillator shown in the diagram uses an operational amplifier (op-amp), three capacitors and four resistors. The circuit's modeling equations for the oscillation frequency and oscillation criterion are complicated because each RC stage loads the preceding ones.
In RC oscillator circuits which use a single inverting amplifying device, such as a transistor, tube, or an op amp with the feedback applied to the inverting input, the amplifier provides 180° of the phase shift, so the RC network must provide the other 180°. [6]
Relaxation oscillators are generally used to produce low frequency signals for such applications as blinking lights and electronic beepers. During the vacuum tube era they were used as oscillators in electronic organs and horizontal deflection circuits and time bases for CRT oscilloscopes; one of the most common was the Miller integrator circuit invented by Alan Blumlein, which used vacuum ...
The output of the amplifier should show a series R driving the first shunt C. That lag network is beyond cutoff so it has almost a 90 degree phase shift (and significant attenuation). The crystal is operated near series resonance, so it looks like a resistor, and that resistor forms a second lag network for almost another 90 degree phase shift.
As the voltage applied to the varicaps is changed, the phase shift of the output will change. Phase modulation is mathematically equivalent to direct Frequency modulation with a 6 dB/octave high-pass filter applied to the modulating signal. This high-pass effect can be exploited or compensated for using suitable frequency-shaping circuitry in ...
For applications in oscillator circuits, it is generally desirable to make the attenuation (or equivalently, the damping factor) as small as possible. In practice, this objective requires making the circuit's resistance R as small as physically possible for a series circuit, or alternatively increasing R to as much as possible for a parallel ...
Output and capacitor waveforms for comparator-based relaxation oscillator A Schmitt Trigger-based implementation of a relaxation oscillator. A Schmitt trigger is a bistable multivibrator, and it can be used to implement another type of multivibrator, the relaxation oscillator. This is achieved by connecting a single RC integrating circuit ...
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