Contents
How does the impedance of a crystal oscillator change?
In the upper image we see the impedance curve of the crystal oscillator and also see that, how this slope changes when frequency changes. There are two points one is series resonant frequency point and the other one is parallel resonant frequency point. At the series resonant frequency point the impedance is became minimum.
Why is output amplification low in quartz oscillator?
The output amplification is low in this configuration for avoiding excess power dissipation in the crystal. Another configuration used in quartz crystal oscillator, where the Transistor is changed to a JFET for the amplification where the JFET is in very high input impedances when the crystal is connected in Drain to Gate using a capacitor.
Why are crystal oscillators used in low power circuits?
The quality factor (Q) of the crystal is very high. They are fragile and can be used in low power circuits. The frequency of oscillations cannot be changed appreciably. An Oscillator is expected to maintain its frequency for a longer duration without any variations, so as to have a smoother clear sinewave output for the circuit operation.
What is capacitor value for quartz crystal oscillator?
One is for primary oscillator for generating the clock and other for the secondary oscillator which is used for other secondary works where secondary clock frequency is needed. The capacitor value range from 10pF to 42 pF, anything in between but 15pF, 22pF, 33pF is used widely.
What kind of transistor is used in crystal oscillator?
Crystal oscillator circuit constructed using bipolar transistor or various types of FETs. In the upper image, a colpitts oscillator is shown; the capacitive voltage divider is used for feedback. The transistor Q1 is in common emitter configuration.
What kind of feedback does a Pierce crystal oscillator have?
In the upper image a Pierce Crystal Oscillator circuit is shown. The C4 provides the necessary feedback in this oscillator circuit. This feedback is positive feedback which is 180 degree phase shift at the resonant frequency. R3 control the feedback and the crystal provides the necessary oscillation.
What is the phase shift of a CMOS crystal oscillator?
The inverter operate at 180 degree phase shift output and the Q1, C2, C1 provide additional 180 degree phase shift. During the oscillation process the phase shift always remain 360 degree. This CMOS crystal oscillator provides square wave output. The maximum output frequency is fixed by the switching characteristic of the CMOS inverter.