Direct FM modulation at VCO with either LMX2531 or LMX2582 PLL lock at 2500MHz

Thomas Lam

Other Parts Discussed in Thread: LMX2531, LMX2582, LMX2541

Hi, I would like to direct FM modulate (~1Mhz) the internal VCO with the PLL lock at about 2500MHz. Phase noise is not a concern but Stability is. Would really appreciate if there is any suggestions or any pitfalls to watch for on using either of the device.

over 9 years ago

0 Noel Fung over 9 years ago

TI__Guru** 107030 points

Hi Thomas,

In LMX2531, the charge pump output is connected to the VCO internally , the applied modulation signal may affect the performance of the charge pump and therefore the stability of the loop.
If the output frequency is fixed in your application, you may try LMX2582. Suggest use active loop filter so that you can have both DC and AC signal coming out from the amplifier at the same time.

0 Thomas Lam over 9 years ago in reply to Noel Fung

Prodigy 50 points

Hi Noel, Really appreciate your quick feedback. Is there any other PLL synthesizes you would recommend for my application since the LMX2582 seems to be overkill if I am not concern about phase noise. Thanks again.

0 Noel Fung over 9 years ago in reply to Thomas Lam

TI__Guru** 107030 points

Hi Thomas,
Would you consider LMX2541?

Clock & timing

Clock & timing forum

Direct FM modulation at VCO with either LMX2531 or LMX2582 PLL lock at 2500MHz