A quartz crystal oscillator teardown with its tiny IC #teardown #ReverseEngineering @kenshirriff
Ken Shirriff provides another interesting teardown and die shot. This is a n encapsulated 4.7174 MHz crystal oscillator found on an old card for an IBM PC.
There is a tiny die inside – magnified, it looks like the image below.
The IC has two functions. First, its analog circuitry drives the quartz crystal to produce oscillations. Second, the IC’s digital circuitry divides the frequency by 1, 2, 4, or 8, and produces a high-current clock output signal. (The division factor is selected by the two select pins on the IC.)
The oscillator is implemented with a circuit called a Colpitts oscillator, which is more complex than the usual quartz oscillator circuit. The basic idea is that the crystal and the two capacitors oscillate at the desired frequency. The oscillations would rapidly die out, however, except for the feedback boost from the drive transistor.
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