COLPITTS Crystal Oscillator Circuit
01 Colpitts Oscillator
I. Introduction
In order to test whether the crystal at hand is normal, we are going to build a crystal oscillator on the breadboard. Use S9018 NPN transistor, which is its basic parameters. The crystal to be tested was actually subjected to an insulation gauge high voltage strike yesterday. This test is mainly to verify that the crystal is still working. The insulation test shows that the crystal after high voltage breakdown still presents an insulating state under low voltage. Use the oscillator to test whether there is any change in the performance of the crystal.
2. Test results
1. Build an oscillator
This is a Colpitts crystal oscillator circuit obtained from the Internet, and the resistance and capacitance parameters will be determined by testing later. Now choose a 12MHz crystal and build this circuit on a breadboard. After adjustment, the parameters of the circuit are finally determined, which are the parameters of the resistors and capacitors in the circuit. Please note that the values of the two capacitors C1 and C2 have been adjusted. Use an oscilloscope to measure the OUTPUT signal of the circuit. ·The signal waveform has many harmonic components. Using a frequency meter to measure the precise frequency of the oscillating signal, it can be seen that the crystal oscillator is still very stable. The frequency value is 12MHz.
▲ 图1.2.1 振荡波形
2. Measure breakdown crystal
This is the crystal that was struck through yesterday with an insulating watch. Next, replace the crystal in the previous circuit with it, and test the output signal of the circuit when it is powered on. It can be seen that the circuit does not work. This shows that yesterday's crystal cannot work after high voltage breakdown.
Next, use an insulation meter to break down the 12MHz crystal in the experiment just now to see if it can still work after the breakdown. Reseat the crystal after breakdown into the circuit on the breadboard. Miraculously, the circuit still oscillates. Only the output waveform changes. The oscillation frequency of the measurement circuit is increased by 3.5kHz compared to the high value. The frequency has increased. The specific reason is not clear.
However, it should be noted that even if another crystal of the same 3.7MHz is replaced, it still cannot oscillate in the test circuit on the breadboard. It can be seen from this that the failure of the circuit to oscillate does not mean that the crystal has been completely damaged in the previous test using a breakdown crystal.
※ Summary ※
This article builds a Colpitts oscillator circuit on a breadboard. ·Use this circuit to test the characteristics of high voltage breakdown crystal. For a 12MHz crystal, this circuit will work. ·But for 3.7MHz crystal, this circuit can't work. - After breaking down the 12MHz crystal with an insulation meter, re-tested, the circuit oscillation frequency increased.
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