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Eugen_E
Joined: 29 Nov 2004
Posts: 358
Helped: 31
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 15 Dec 2004 22:15 20 mhz vco |
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Hi all!
I want to design a wide range (2-20MHz) discrete VCO, as part of a PLL frequency synthesis and I need some ideas.
I think there are few ways to do this:
1. A oscillator controlled with wide range varactor diodes ---but I can't find special varactors to use---
2. Mixing 2 higher frequency signals, for example one at 100MHz and the second from a 102-120MHz VCO (controlled with "normal" range varactors) ---but the schematic is more complex and the output signal contains more harmonics---
3. Using a ring oscillator, which is suitable for IC design.
So, who can help me with some ideas in designing this VCO with general purpose parts and a moderate complexity schematic? I appreciate your help!
Thanks in advance!
Best regards,
eugen
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CDRCDR
Joined: 15 Feb 2004
Posts: 82
Helped: 2
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16 Dec 2004 1:57 wide vco |
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| A ring oscillator in general can help you with that range.If not,you could further use mixer to generate the frequency that you want.
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Eugen_E
Joined: 29 Nov 2004
Posts: 358
Helped: 31
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19 Dec 2004 17:27 vco 20mhz |
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I need to design a discrete VCO and I don't want to use the mixer choice because of the complex schematic, the need for precise measurements and tuning and the harmonics present in the output signal.
I want to use a classical LC oscillator and I think I should use "something" that will replace the hard to find wide range varactors.
So I want to ask if you know a method to obtain a wide tuning range by controlling the capacitance, inductance, or both with a voltage.
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19 Dec 2004 17:27 Ads |
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ddt694
Joined: 12 Dec 2002
Posts: 175
Helped: 5
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19 Dec 2004 17:40 vco wide |
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| you can use 74hc4046, a very popular pll device which includes two PD and a vco.
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FANT
Joined: 27 Feb 2002
Posts: 367
Helped: 12
Location: Italy
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19 Dec 2004 17:43 20mhz vco |
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I think that a traditioonal approach is not possible, because the frequency range is nearly ten times and this requires a change in capacitance of 100 times ( excluding the capacitances of the circuit. )
An easier approach is with the old CD40HC46 of in a new fashion with the DDS AD 9850.
Mandi
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