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i need to construct a vco that generates a range of frequencies from 2 MHZ to 12 MHZ with a step size of 100khz..............
we can tune the vco on a fixed frequency and can use the divider circuits for this purpose.
but the problem is i dont have any idea from where to start...note:i cant use any crystal
---------- Post added at 09:54 ---------- Previous post was at 09:53 ----------
i need to construct a vco that generates a range of frequencies from 2 MHZ to 12 MHZ with a step size of 100khz..............
we can tune the vco on a fixed frequency and can use the divider circuits for this purpose.
but the problem is i dont have any idea from where to start...note:i cant use any crysta
Since you can't use any crystal, you can't use VCO, because VCO need crystal for reference.
So you can use DRO, then use divider, say DDS, to implement it. But this plan maybe two expensive.
If your requirement is not so high, you can use 555 to implement OSC. You can try to start from 555.
You can try to use the internal VCO of 74HC4046, which is about this frequency range.
For your application you can use the same 4046 PLL circuit, using an LC oscillator for 100kHz reference frequency (no crystal), which will be your frequency step.
now i have decided to use a crystal as without crystla it is not easy to achive.......please guide me what value of crystal i shud choose...and pll IC and divider ic which gives me a step size of 100khz.....as i have to make hundred channels from 2MHZ to 12 MHZ........
thnx...but i can not use a crystal of value between 2MHZ and 12MHZ as it will produce a notch in the desired band of frequencies.....and it ll not be easy to remove
ma main problem is i can not find the exact pll ic and a programmable divider ic...as i have to make 100 channels out of 2MHZ to 12MHZ....at any time by using divider i could select any channel say i want to select 10.7MHZ(for example)
Assuming you won't get a complete PLL IC for the intended frequency range, at least I'm not aware of any, you can design the PLL from multiple IC. 74HC4046 would be a VCO for the frequency range, so you need a reference oscillator and a divider in addition. I implemented the logic part of a similar PLL design with a CPLD, but you can also use individual 74HC logic ICs. Some microcontrollers also have a suitable timer channel.
PLL IC you can select ADF4360-9, then select a VCO, design PLL loop circuits, ADF4360-9 have already have a divider. For more divider, you can ref Hittite or Mini-Circuits website.
The programmer IC you can use Freescale product.
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