3rd overtone xtal osc.
时间：04-05
整理：3721RD
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iam trying to make a crsytal oscillator as reference for PLL
the crystal has fundamental 40Mhz which is not suitable to work at for certain specs in PLL, it should work at 3rd overtone (120MHz)
i need help in modeling the xtal plz
knowing that co (shunt cap)=5pF
cload=15PF
i got the values at 120MHz : Lm=3.52m , cm=0.2f
actually it is not oscillating because at high freq impedence of sunted cap c0 is too small (shorting the series Lm , cm , Rm)
the solution is to use another Lo to be shunted to co to remove that effect but the value of Lo would be 0.35u which is not integrated on chip , what can i do ? help me plz
can any one post me a practical on chip schematic for such oscillator, thnx
the crystal has fundamental 40Mhz which is not suitable to work at for certain specs in PLL, it should work at 3rd overtone (120MHz)
i need help in modeling the xtal plz
knowing that co (shunt cap)=5pF
cload=15PF
i got the values at 120MHz : Lm=3.52m , cm=0.2f
actually it is not oscillating because at high freq impedence of sunted cap c0 is too small (shorting the series Lm , cm , Rm)
the solution is to use another Lo to be shunted to co to remove that effect but the value of Lo would be 0.35u which is not integrated on chip , what can i do ? help me plz
can any one post me a practical on chip schematic for such oscillator, thnx
The normal method used in Butler config overtone oscillators is to place a shunt L of 350nH across the xtal.
Also I'm curious to know where you got a crystal which has a fundamental of 40Mhz ?