connect between LVPECL & VML

Zhang wei1

Prodigy 60 points

Hi,

We use TLK 2541, and the signal input from optical module.

The output is LVPECL.

The input of TLK2541 is VML.

The TLK2541's input common mode range is from 1000 mV to 2250 mV

The output swing generated by optical transceiver is 800mV

The common voltage generated by optical transceiver is about 2000mV.

Our schematic attached. But it seems that the swing is too small.

We try to connect them directly, it not works.

How to connect with them if we want to use DC couple?

Thanks.

12 年多前

0 Seasat Liu 12 年多前

TI__Mastermind 30930 points

看一下这个链接里的东西。这个是将如何LVPECL和VML链接的文档

www.ti.com.cn/.../litabsmultiplefilelist.tsp

0 Felix Wei 12 年多前

TI__Prodigy 480 points

Hi, Wei

Assuming the VCC=3.3 in your schematic, the DC bias of the transceiver is about 1.28V, which is conflict with the 2V common voltage generated by optical module. If you wanna keep the bias network, you should add some capacitance to form a AC coupling.

0 Zhang wei1 12 年多前回复 Felix Wei

Prodigy 60 points

Vcc=3.3V

Can we make some change to use DC coupling?

Ths.

0 Felix Wei 12 年多前

TI__Prodigy 480 points

Hi, Wei

As TLK2541 is internal terminated, you can just connect the TX and RX directly without any other components if you wanna use a DC coupling.

If it didn't work, you can just replace the R402 and R493 with two capacitance. It is just much simpler than your schematic above.

If you insist on DC couple, you should check the voltage and current along the wire connecting TX and RX. Finding out whether the DC bias is still comply the input DC range defined in datasheet.

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connect between LVPECL & VML