LMX25311570EVAL: Loop bandwidth of the EVM

Sam Huang32

Part Number: LMX25311570EVAL
Other Parts Discussed in Thread: TINA-TI

Hi all,

According to the instruction of EVM, the loop bandwidth is 4.8KHz. However when I simulate the loop filter circuit on TINA-TI, the result is beyond my expectation.

The cut off frequency is around 14-15KHz. Maybe I misunderstand the definition of loop bandwidth?

over 7 years ago

0 Dean Banerjee over 7 years ago

TI__Mastermind 28021 points

Sam,

According to the PLLatinum Sim tool (http://www.ti.com/tool/PLLATINUMSIM-SW, the loop bandwidth is 4.8 kHz and the formulas used to this are in my online PLL book at http://www.ti.com/tool/pll_book . We define the loop bandwidth as the frequency where the magnitude of the forward loop transfer function (Kpd*Kvco/(N*s)*Z(s) ) is one. From your plot, it looks like you are definining it as the point where the gain is 3 dB down -- not the same as our definition.

Regards,
Dean

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LMX25311570EVAL: Loop bandwidth of the EVM