LMX2820: Duty Cycle for PFDIn and OSC_IN

Izik

Part Number: LMX2820

We are using the device with direct input of the feedback signal to PFDin pin.

The reference is connected to OSC in.

Both inputs are single ended 50ohm.

Both signals arrive from saturated amplifiers which generate even and odd harmonics, which transform in time domain to square wave with 65% duty cycle.

Is there an importance to the duty signal of both signals? - besides the comment about the OSC doubler spurs.

Thanks

over 3 years ago

0 Noel Fung over 3 years ago

TI__Guru** 122040 points

Hi Lzik,

If you do not use OSCIN doubler, duty cycle of OSCIN signal is not matter.

The duty cycle of the feedback path signal (in this case, PFDIN), is also not important to a PLL.

0 Izik over 3 years ago in reply to Noel Fung

Expert 1585 points

Ok, even if they won't have the same duty cycle necessarily? One can be 50% and the other input 65 %

Thanks

+1 Noel Fung over 3 years ago in reply to Izik

TI__Guru** 122040 points

Hi Lzik,

Yes, the phase detector will compare the phases between input and feedback path whenever it see a rising edge from the input path, so duty cycle is not matter.

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LMX2820: Duty Cycle for PFDIn and OSC_IN