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Eric Weaver wrote:
So pardon my ignorance, what's the hip PLL or at least counter/phase-detector these days? Hip these days is not to use a PLL but use an NCO. Of course there are differences in the spurious and noise output. However, when still using a PLL and using it for amateur purposes (small steps relative to the frequency), at least go for a dual-modulus system. Else the phase comparator has to operate at the frequency of the channel step, or even at a fraction of that when a fixed prescaler is required in front of the programmable divider. As the MC145151 at best operates up to 25 MHz, you often will require a prescaler. A low phase comparator frequency means a slow loop. The MC145152 is a dual-modulus version. However, note that with a dual-modulus system it is more complicated to generate the setting information, probably requiring a microcontroller. Once you are going to need that, it is easier to use a more modern IC programmed using I2C. |
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