Colpitts Crystal Oscillator

hey what's happening guys today we're going to talk about crystals crystal oscillators specifically the Colpitts oscillator which was invented in 1918 by Edwin Colpitts and it's distinguishing feature oops starting to bump the camera there is that eases a voltage divider made up of two capacitors okay a little bit of an interesting circuit design so let's draw it out here so here we have in this case our five volt rail and from our five volt rail we're going to come down to a resistor and then we will have our crystal and then we have our ground rail for zero volts next we're going to have a load resistor and then our capacitor divider these three parallel circuits here are going to feed into the base of an NPN transistor with the collector going to the five volt rail and the emitter going through a resistor to ground and then our voltage divider I'm going to come up here just like that and we can take our output right there so the values that I'm using for this oscillator are 33 K 33 K 220 picofarad 220 picofarad this is a 2.2 K and this is a 2 n 2 2 2 2 NPN transistor now the values here can be somewhat ballpark but you do want to keep them in the same range especially the load capacitors and those load resistors there you do want to keep them somewhat the same or you're going to run into problems all right so let's bring in the circuit that I have read boarded up here and we can take a closer look at it so here is our circuit where's my stick oh there it is so we have our first 33 K resistor coming down to one side of the crystal and then we have going on in parallel the other 33 K resistor which if you follow here goes directly to ground and then coming out in parallel also is our capacitive divider network going to ground and then we have also coming out of the same side so it's in parallel is this line going to the base of our transistor just want to knock that out of there we have the collector of the transistor transistor going to our five volt rail and the emitter coming down here through that 2.2 K resistor in the ground and then this is where we can take our reading so let me hook this up to the oscilloscope and then we will take a look at it so first I'm going to power up or I'm going to connect the ground and then our lead like that and let's swing on up here to the oscilloscope and zoom in here a little bit so there we have our Colpitts oscillator oscillating on the oscilloscope and you can see the frequency here is twenty six point nine nine five four megahertz and it is a very stable oscillation we bring up our measurement window we can see a period of 37 nanoseconds 50% duty cycle our peak to peak here is 704 millivolts and our pulse width is 19 nanoseconds so guys girls whoever else may be watching I think we have now covered just about every type of oscillator that you're going to come across in polite society or you know if you're an engineer not so polite society and that's about it if you guys enjoyed this I hope you'll give me a thumbs up feel free to comment ask any questions I'll try and answer them as best as I can and please help me out and share one of my videos somewhere help grow the channel you know the more subscribers I get the more sponsorships I get the more neat stuff that we can play with and I do have some neat stuff coming up including a Bluetooth controlled music playing light bulb but that's going to be a few weeks away it just left Shenzhen yesterday alright I hope you guys all have a fantastic Father's Day and I'll talk to you next time

Channel: learnelectronics

Views: 102,389

Keywords: colpitts, crystal, oscillator, clock, circuit, tutorial

Id: r2FoDw_h5RU

Length: 8min 0sec (480 seconds)

Published: Sat Jun 17 2017