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https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> Bandwidth of Oscillator https://designers-guide.org/forum/YaBB.pl?num=1321479475 Message started by Brandon on Nov 16th, 2011, 1:37pm |
Title: Bandwidth of Oscillator Post by Brandon on Nov 16th, 2011, 1:37pm Attached is schematic of oscillator whose output frequency depends on the LC tank circuit. The inductance by which this oscillator seems to be 'stable' is 1nH - 10mH. I need to know what is the purpose of the negative feedback with a bypass capacitor to ground and the purpose of the resistor network on top. Is there an effective way to modify the circuit to handle higher inductor values? thanks |
Title: Re: Bandwidth of Oscillator Post by raja.cedt on Nov 16th, 2011, 1:58pm hello, 1.What is your Frequency of interst? Why you want to maximize the L, you dont have smaller inductors? 2. -ve feedback(at least DC) through is essential because you need -ve resistance to compensate finite Q of the tank. Top resisters are for biasing the opamp i guess. 3. Try to post small schematics so that it will easier to view. Thanks, Raj. |
Title: Re: Bandwidth of Oscillator Post by Brandon on Nov 16th, 2011, 2:25pm This oscillator will be used to determine the value of inductance or capacitance by measuring the output frequency from a microcontroller. That is why I need to increase the bandwidth. The circuit is attached again. |
Title: Re: Bandwidth of Oscillator Post by aaron_do on Nov 16th, 2011, 11:14pm Hi Brandon, I think the negative feedback is used to provide a DC bias to the negative input pin of the op-amp. If you want the circuit to work for higher L values, maybe you can increase the size of the two large capacitors. You should simulate it to verify. regards, Aaron |
Title: Re: Bandwidth of Oscillator Post by buddypoor on Nov 16th, 2011, 11:59pm Yes, of course the negative R-C feedback is necessary to ensure a bias point at approx. half of the supply voltage. This is the clasisical bias concept for single supply circuits: DC bias at the pos. input and negative feedback for dc unity gain of the opamp. |
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