Guest
I have electronics hobby and just start learning how oscillator works,
like the loop gain must be >= 1 and the phase between the input and
output should be 0 degree. The problem is, when I see the actual (even
simple) oscillation circuit, I am at a loss how it exactly works.
"http://img13.imagevenue.com/loc70/a2a_osc123.jpg"
For example, in Fig.1, what's the use of resistor R2, from oscillation
point of view (not from transistor DC basing point of view)? I figure
that, since C3 is basically to short AC (i.e. RF in this case), it
seems to be equivalent to place one end of the crystal directly to the
emitter, as shown in Fig.2. Unfortunately, it does not oscillate this
way. Likewise, since C3 is to short the AC, then it should also be OK
to remove R2 and C3 completely, and place the crystal in a way shown in
Fig.3. However, it does not oscillate, either.
(1) So what is the function of R2 here?
(2) If it is a must for the oscillator to work, how to choose it?
(3) How to choose the value of C3?
Your help is appreciated!
like the loop gain must be >= 1 and the phase between the input and
output should be 0 degree. The problem is, when I see the actual (even
simple) oscillation circuit, I am at a loss how it exactly works.
"http://img13.imagevenue.com/loc70/a2a_osc123.jpg"
For example, in Fig.1, what's the use of resistor R2, from oscillation
point of view (not from transistor DC basing point of view)? I figure
that, since C3 is basically to short AC (i.e. RF in this case), it
seems to be equivalent to place one end of the crystal directly to the
emitter, as shown in Fig.2. Unfortunately, it does not oscillate this
way. Likewise, since C3 is to short the AC, then it should also be OK
to remove R2 and C3 completely, and place the crystal in a way shown in
Fig.3. However, it does not oscillate, either.
(1) So what is the function of R2 here?
(2) If it is a must for the oscillator to work, how to choose it?
(3) How to choose the value of C3?
Your help is appreciated!