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You first need to decide on the topology of the oscillator itself. This is dictated by the target complexity and oscillator performance requirements. Then you need to define what problem you are trying to solve by employing an AGC loop (potentially this problem isn't a real problem, or it can be solved in a different way). If AGC is still required, then you need to assess the loop control bandwidth to counter the amplitude effects that limit your target performance.
About a crystal model: it is best that you contact the target crystal manufacturer for that, since there are large variations (related to fund. or overtone, package type and parasitics, the way the crystal is cut, specified loading capacitance, etc.). There doesn't exist any standard crystal model. You really have to target some specific vendors and types.
First thanks for your reply
second wrt topology of oscillator ,it is cmos oscillator 0.13 technology and 1.2V supply voltage , specs required are 25 Mhz frequency high stability .very low phase noise and low power dissipation
third Agc loop required to give a very large starting current at start up phase of oscillator then at steady state give the circuit a very low current
this to decrease settling time
forth crystal model , i want at the first any real equivalent circuit of crystal to use it now in simulation
thanks alot
thanks for your reply but i want model of 25 MHz it is not included
and i have another question what make circuit operate in parallel or series resonance
i put model of 10Mhz in cadence with pierce circuit and operate series resonance and the same model with collpit operate parallel resonance.
One more thing: AGC circuits may be complex in some implementations, so if the only purpose is to guarantee quick startup while proving low operating current in normal operation, you can also consider to make a low-current oscillator, with temporary current boost at startup (triggered by POR, VDD or a digital circuit)
Added after 3 minutes:
For 25MHz, I suggest you take the 30MHz suggested values and adjust L1 to resonate with C1 (6fF) at 25MHz. So L1=1/(w^2*C1), where w=2*pi*25e6, so L1=6.7547mH.
About series/parallel: this is dictated by the circuit topology (the nature of the feedback loop). The oscillation criterion is that the loop gain >1 and phase=0 at oscillation. If this criterion is met by parallel or series determines the mode of oscillation.
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