SN65LVDS125A: output waveform is not symmetrical

Cickey Xu

Part Number: SN65LVDS125A

dear TI buddy

my customer used SN65LVDS125A to design a lvds project, but the output waveform is not symmetrical,besides,the output amplitude(Vpn) is only 100mv when i connect the LCD panel,if disconnect the LCD,the output ampitude is about 300mv.

the attachment is schematic and the output waveform.

can you help me explain why like this? and how should i resolve the issue.

thanks.

best regards

Cickey Xu20150706162546SG205-J0-304.pdf

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 243180 points

Were these waveforms measured before or after the RCLAMP/ESD components?

What are the characteristic impedances of the traces, and of the connector? Are they impedance controlled?

How are the LCD inputs terminated?

0 Cickey Xu over 5 years ago in reply to Clemens Ladisch

Intellectual 656 points

Hi,Clemens,

the waveform is after the RCLAMP/ESD components,that is to say we measure the signal at E0_P1/E0_N1,

about the impedances ,customer cant measure;

LCD input terminate is CN1(P50-2D54-NJ ),they connect the LCD by row needle.

i think this is impedance match issue,how should i adjust our SN65LVDS125A's output impedance.

0 Clemens Ladisch over 5 years ago in reply to Cickey Xu

Guru 243180 points

Are the waveforms better before the RCLAMP/ESD components?

Does the LCD datasheet say anything about the termination/impedance?

Adjusting the output impedance is possible only if the desired impedance is known.

0 Cickey Xu over 5 years ago in reply to Clemens Ladisch

Intellectual 656 points

customer cant get the lcd input impedance;they also have good method to measure the impedance.
but they can adjust SN65LVDS125A's impedance to match the LCD input impedance. so can you tell me how to adjust our SN65LVDS125A's output impedance?

0 Clemens Ladisch over 5 years ago in reply to Cickey Xu

Guru 243180 points

To increase the impedance, add a resistor.

But if the characteristics are not known, it would be a better idea to add a common-mode choke.

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SN65LVDS125A: output waveform is not symmetrical