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zhangm79
Joined: 05 Apr 2006
Posts: 28
Helped: 1
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 05 Nov 2009 13:50 Why too low frequency of Negative capacitor using opamp? |
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hi, all. I need realize negative capacitor from 80MHz to 108 MHz by NIC using opamp, the opamp 3-dB bandwidth is 150MHz. But the negative cap can be got under 1.5MHz.
Anyone can help to explain why?
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zhangm79
Joined: 05 Apr 2006
Posts: 28
Helped: 1
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06 Nov 2009 4:02 Why too low frequency of Negative capacitor using opamp? |
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| anyone can help?
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06 Nov 2009 4:02 Ads |
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kspalla
Joined: 19 Aug 2008
Posts: 848
Helped: 140
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06 Nov 2009 10:18 Why too low frequency of Negative capacitor using opamp? |
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| Can you share the design?
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FvM
Joined: 22 Jan 2008
Posts: 5160
Helped: 767
Location: Bochum, Germany
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06 Nov 2009 13:45 Why too low frequency of Negative capacitor using opamp? |
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I doubt, that the loop bandwidth will be 150 MHz, I guess, it's rather the unity gain bandwidth respectively GBW product.
In any case, a much higher OP bandwidth would be necessary to generate almost capacitive behaviour.
Circuit stability is another topic.
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zhangm79
Joined: 05 Apr 2006
Posts: 28
Helped: 1
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10 Nov 2009 14:15 Why too low frequency of Negative capacitor using opamp? |
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| Thanks a lot. I change to LMH6703, and simulated by ADS, achieve good negative capacitor in FM band. I would upload the design after testing
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