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https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> Need help with my circuit https://designers-guide.org/forum/YaBB.pl?num=1262597407 Message started by sk.shawn on Jan 4th, 2010, 1:30am |
Title: Need help with my circuit Post by sk.shawn on Jan 4th, 2010, 1:30am Dear all, I'm seriously having problems with this circuit (as attached) that I'm designing at the moment. The topology is based on a paper reported in solid state journal and the working principle is to linearize my open loop VCO by negative feedback using a switched capacitor network that is acting as a frequency to voltage converter (FVC). The issue is can Vin be a DC signal? As soon as I feed a DC input, the opamp output is immediately saturated. I'm just all confused about the type of input signal that should be fed. Ultimately, the range of voltage that I would like to have at the opamp output is 1.2V to 2.2V which I have no idea of how to achieve this. I have tested all individual blocks separately and they are all working (opamp, FVC, open loop VCO). I feel that it could be just some minor thing that I need to get it figured out. So, I'm hoping someone here can shine some light to assist me. P.S Vin is a negative input and Vp is grounded according to design in paper. Sorry for the long type. Any help is appreciated greatly. Thanks a million. Regards, Shawn |
Title: Re: Need help with my circuit Post by raja.cedt on Jan 4th, 2010, 3:53am hi, can you please tell me the name of the pap,so that i can also read. The problem could be lack of -ve feedback (because you are opearting circuit in open loop), if that fvc block is providing -ve feedback then its fine. So just check whats that block polarity? Thanks, Rajasekhar. |
Title: Re: Need help with my circuit Post by Mayank on Jan 4th, 2010, 3:58am Hi shawn, i worked on a similar ckt.... Answers to your queries -- Quote:
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My assumptions from ur post :-- 1. Quote:
My Questions :--- 1. Quote:
2. Why do you need such a linear VCO ?? General Practice :--- We avoid these kinda circtuits generally because of power and area overhead...If you wanna alter you Kvco, do it by directly altering the current fed to the oscillator. We generally dont need very high-linearity in Ring-Osci VCO's. [ Again I assume that you are using Ring Osci. ] We just ensure the VCO Frequency Tuning with Vcont is Monotonic ie varies in just one direction. Hope it helps, Mayank. |
Title: Re: Need help with my circuit Post by sk.shawn on Jan 4th, 2010, 6:15am raja.cedt wrote on Jan 4th, 2010, 3:53am:
Hi Rajasekhar, Thanks for the reply. I have attached the paper for your reference. Basically, my circuit is based on the topology mentioned in this paper. The FVC is implemented as a simple switched capacitor network. A lot of my peers have told me that this circuit is rather straightforward but I just can't get it to work in the way I want. Anyway, appreciate your support. Hope to hear more views and opinions. Regards, Shawn |
Title: Re: Need help with my circuit Post by sk.shawn on Jan 4th, 2010, 6:38am Hi, Thanks a million for replying in sequence. I have attached the paper here in my earlier reply to Raja. My circuit is based on the topology discussed in that paper. Quote:
I thought of this too and actually included this into the circuit. However, as reported in the paper, the feedback resistor was not included by the author. So, I was contemplating if this was a correct move. So, in this case, a feedback resistor is required then? Quote:
Perhaps, the image I attached was unclear. Vin is a negative input applied to one of the terminals of the resistor. It will be clearer if you look at the circuit in the paper. Sorry about that. Quote:
The FVC is implemented as a simple switched capacitor network. Will current be an issue here? Sorry I didnt really check this out. But i will perform a simulation and see. Thanks! All in all, I need a highly linear VCO to realize a time based ADC where other constituents blocks will come together as well. Once again, thanks for the help and effort in replying. Please continue to assist me. I will be more than glad to provide more information if required. Thanks a million |
Title: Re: Need help with my circuit Post by Mayank on Jan 4th, 2010, 10:39am Hii, @ raja : I came up with this idea on my own some time back, frequency controlled resistor using S-C and resistive comparison....It's cool as well as disheartening to know someone's already worked on it. :( Although, the ckt i came up with is a lot different frm this. But linearity was my secondary objective. Quote:
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-- Mayank. |
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