Preamplifier up and running!

A project log for Frequency-Modulated Atomic Force Microscope

Quartz tuning fork-based FM-AFM

Dan BerardDan Berard 07/23/2015 at 02:490 Comments

Got the preamplifier PCB in from OSHpark the other day and soldered it up.

Hooked up a 32.768 kHz crystal and fed in a sine wave from a function generator. A few hundred mVpp is attenuated by a factor of 100 by the preamp to drive the crystal. Resonant frequency of this particular crystal is 32.7634 kHz. The waveform shown below is the preamp output of several Vpp. There's a ton of noise on it from the SMPS I'm currently using to power it. This will be replaced with a linear supply eventually.

The Q of these oscillators is quite high, but will decrease once removed from the metal can. The resonant frequency will also decrease by a few kHz when exposed to air. I was concerned about bandwidth with the 10M feedback resistor, but it turned out not to be a problem at all. Should be able to use 100 kHz or even 200 kHz tuning fork.

Here's the PCB on OSH Park: