First you fail to list several parameters such as accuracy and jitter. These are very important parameters in determining which type of circuitry to use.
Second, you can use a PLL. It is not necessary to be harmonically related. You only need one common denominator (try 100KHz) . This will be the best solution if you need and phase coherency. However that may be a difficult design for 3 frequencies.
If you indeed have a solution costing $1.30 that works I would be inclined to stick with it. I can't buy three non-standard crystals or quality PLL components for that price.
Fred Townsend
Jens Sch�nfeld wrote:
Hi,
I'm designing a circuit that needs three different clocks at the same time:
28.3 Mhz 17.7 Mhz 14.3 Mhz
As you can see, none is a multiple of the other, so a PLL won't really help me. I'm currently at one 74HCU04 with the respective crystals and caps as an oscillator, costing about 1.10 EUR in production for all three clocks. For this kind of money, (roughly $1.30) I think I can have something more sophisticated than the discrete oscillators, maybe with some spread-spectrum for EMI control.
My FPGA has 3.3V, 5V-tolerant IOs.
Ideas, anyone? Maybe something programmable? I need more than 1200 units, and I have about five weeks time before I need the quantity.
thanks,
Jens
-- Author: Fred Townsend INET: [EMAIL PROTECTED]
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