Actions
Forum Thread Details
  • State Verified Answer
  • Replies 18 replies
  • Answers 1 answer
  • Subscribers 111 subscribers
  • Views 6320 views
  • Users 0 members are here
Related

Colpitts Crystal Oscillator Circuit

jw0752

In the last couple days I have been experimenting and learning about crystal oscillator circuits. I am doing this with no particular application in mind. I have been able to get a couple circuits to work as expected but there is one circuit that I got from the book " Practical Electronics for Inventors" by Paul Scherz and Simon Monk that I have not been able to get working. I have tried different transistors and I have tried varying the values of the support passives. I am wondering if anyone has had experience with this circuit and can give me a hint as to where to look for my failure to get it to work. There is also one other possibility. This book has been known to include errata from time to time so I wouldn't be completely surprised if there is something wrong with the circuit. Any insights would be appreciated.

 

John

 

 

image

Parents
  • 0

    Hi John,

     

    I tried the circuit just now too, and experienced failure with it just like you. You're right, the circuit is incorrect, probably never tested. The reason is the transistor : ( According to the datasheet (I checked PN2222, which is the plastic version of the 2N2222, which is what I had), it has current gain-BW product of 300MHz, i.e. at 10MHz, the gain (AC small-signal gain) would be not higher than 30. However, this is not likely either, because this is spec'd at 20mA collector current according to the datasheet, so the actual gain will be lower still.

    I fiddled with the circuit before I realized this, and it still didn't work. However after swapping out with a BF199 (550MHz fT, spec'd at 5mA), it worked. However now my circuit is slightly different from yours. I'll draw it up, and then move the components on the breadboard back to the original circuit (but with BF199) to see if it still works.

    (I tested with a radio).

    However, as I understand, BF199 is a European transistor. Hopefully you can still get it easily in the US, otherwise an alternative is needed.


Reply
  • 0

    Hi John,

     

    I tried the circuit just now too, and experienced failure with it just like you. You're right, the circuit is incorrect, probably never tested. The reason is the transistor : ( According to the datasheet (I checked PN2222, which is the plastic version of the 2N2222, which is what I had), it has current gain-BW product of 300MHz, i.e. at 10MHz, the gain (AC small-signal gain) would be not higher than 30. However, this is not likely either, because this is spec'd at 20mA collector current according to the datasheet, so the actual gain will be lower still.

    I fiddled with the circuit before I realized this, and it still didn't work. However after swapping out with a BF199 (550MHz fT, spec'd at 5mA), it worked. However now my circuit is slightly different from yours. I'll draw it up, and then move the components on the breadboard back to the original circuit (but with BF199) to see if it still works.

    (I tested with a radio).

    However, as I understand, BF199 is a European transistor. Hopefully you can still get it easily in the US, otherwise an alternative is needed.


Children
No Data