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The Colpitts oscillator

2016-08-09 11:43  
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The Colpitts oscillator
Figure shows the Colpitts oscillator circuit. It has a base frequency crystal, and the frequency is 1499 kHz, crystal SJT is connected to the both ends of capacitor C2, C3. Emitter divider resistor R2, R3 provide basic feedback signal, the feedback voltage is controlled by the capacitive dividers C2, C3. SJT crystal provides l499kHz sine wave signal for the base of the transistor VT after working. And it is output by VT emitter output VT. Resistors R1 provides a 18V step-down voltage for a proper bias voltage of VT, appropriately adjusting resistor R1 could make Colpitts oscillator work in the soft excitation state. Resistor R4, capacitor C5 is post-coupling circuit. Regulating capacitor C1 can fine-tune the oscillator working frequency. Adjusting potentiometer RP can change the oscillation signal output level. Selecting components: capacitors Cl, 5 ~ 20p, C2 to 51p, C3, C6 to 100p, C4 to 15p, C5 is 100μ/32V. Resistor Rl is 62kΩ, R2 is 300Ω, R3 is 2.4kΩ, R4 is 360Ω, 1/2W, R5 is 15kΩ. Potentiometer RP is 4.7kΩ. Transistor VT is 3DGl20C, 65 ≤ β ≤ 115. Zener diode VD uses 2CW58. crystal SJT uses JA5B-1499Hz.