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| How to determine if PLL 4046 is locked? |
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| ZeroResistance:
:horse: --- Quote from: Benta on August 12, 2018, 10:16:36 am --- --- Quote from: ZeroResistance on August 12, 2018, 05:41:28 am --- I was under the impression that when both VCO and Signal In are in phase the phase comparator should have output 0 volt's. --- End quote --- No. From your link: "The phase locking itself works by using an XOR gate to detect the phase angle between the two inputs, pin 3 and 14. The output from the XOR (pin 2) is a PWM signal, and the duty cycle will vary from 0 to 100% as the phase difference between two 50% duty square waves moves from 0 to 180 degrees." --- End quote --- OK, so lets see if the VCO out is the same frequency as "Signal IN" but 180 deg out of phase, at this point PFD1 out will be high continuous right? and this will cause VCO frequency to increase this the Both VCO and Singal In are locked in phase but different frequencies right? So does this PLL have 2 modes of operation Locked Phase and Locked Frequency? |
| Benta:
--- Quote from: ZeroResistance on August 12, 2018, 12:39:13 pm --- So does this PLL have 2 modes of operation Locked Phase and Locked Frequency? --- End quote --- No, not quite. First, it does not make sense to analyze an out-of-lock situation, because that is chaotic. When in lock, input and VCO frequency are the same, and the phase difference between them is constant. The difference between PD I and PD II is, that for PD I, the phase difference is constant, but varies with frequency, as it needs to provide a PWM signal that can be filtered to a DC voltage for the VCO. For PD II, the phase difference is always zero, and the output is three-stated most of the time. This is also one of the reasons why you need an active loop filter. Please note, that for PD I to function correctly, the input must either be a sine wave or a 50% duty cycle square wave. |
| ZeroResistance:
So for a high frequency verson (5Mhz to 15Mhz) of the CD4046 what would be better? 74HC4046 74HCT9046 74HC7046 AD9901 Or are there any other better alternatives? Even a purely digital version would do I can add it to the list :) EDIT: The AD9901 seems to be PFD and not a full fledged PLL :( |
| Kleinstein:
Speed wise there is not much difference between HC4046 / HC7046 und 74 HCT ... Choosing the manufacturer could have a larger effect. There are quite a few modern PLL Chips, many of them much faster, like in the GHz range. ADF4351 is one such example. PLLs are also integrated into quite a few µCs. |
| Benta:
--- Quote from: ZeroResistance on August 14, 2018, 07:34:12 pm ---So for a high frequency verson (5Mhz to 15Mhz) of the CD4046 what would be better? --- End quote --- Neither the CD4046 nor the 74HC types will work well at those frequencies. I think you need to take a step back and rethink this project. |
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