LMH0344: I have used the IC LMH0344 and observed the noise

Mateer Bhat

Part Number: LMH0344

Hi Team,

I am using the LMH0344 IC and have a few questions.

1. I have single ended input and output. As per the schematic attached, i need the single ended output. Can you please go through the attached schematic and let me know why i am getting the noise. I have attached the video for your reference.

The output is getting connected to the graphics card as input.

over 1 year ago

0 Nasser Mohammadi over 1 year ago

TI__Guru* 93670 points

Greetings,

Please zoom into your schematic so we can easily see component designator and values.

Thanks , Nasser

0 Mateer Bhat over 1 year ago in reply to Nasser Mohammadi

Prodigy 40 points

Dear Nasser,

Please find attached the schematic in PDF format.

The camera output is connected to the LMH_S2_J2_B1_SDI3_IN signal, and the QMS_S2_J2_B1_SDI3_IN signal is connected to the input of the graphics card. I have attached the block diagram of the graphics cards. The QMS_S2_J2_B1_SDI3_IN signal is connected to the SDI1_IN to the graphics card and SDI1_OUT is the output of the graphics card (CW_VPX3-719_HUM_837068v4-14.pdf) . When we connect the SDI1_OUT signal to the HD-SDI monitor it shows the noise. (video shared previously).

CW_VPX3-719_HUM_837068v4-14.pdf

.MS_IOTP_SCH_REVC-25.pdf

Regards,

Mateer Bhat

0 Nasser Mohammadi over 1 year ago in reply to Mateer Bhat

TI__Guru* 93670 points

Hi Mateer,

1). Please change R433 to 49.9-ohm Resistor.

2). Please note output should be impedance controlled and either 100-ohm differential or 50-ohm single ended.

3). SDI input - from BNC to C455 - should be impedance controlled - 75-ohm.

4), R481 and R482 are not recommended since these would connect 75-ohm to 50-ohm impedance controlled signals.

Please note section 8 through 10 of the data sheet:

https://www.ti.com/lit/ds/symlink/lmh0344.pdf?ts=1676411763522&ref_url=https%253A%252F%252Fwww.ti.com%252Fsitesearch%252Fen-us%252Fdocs%252Funiversalsearch.tsp%253FlangPref%253Den-US%2526searchTerm%253Dlmh0344%2526nr%253D119

Regards,Nasser

0 Mateer Bhat over 1 year ago in reply to Nasser Mohammadi

Prodigy 40 points

Hi Nasser,

We changed the R433 to 49.9-ohm Resistor and removed R481 and R482 as you said its not recommended since these would connect 75-ohm to 50-ohm impedance controlled signals but we still observed the noise. But the noise was very less. When we tested we set the MUTEREF signal unconnected.

The data sheet said MUTEREF may be either unconnected or connected to ground for maximum equalization

Do I need put t put 1k Resistor between MUTE_REF signal and GND.(location - R436).?

Do you have any other inputs about this noise issue?

Regards,

Mateer Bhat

0 Nasser Mohammadi over 1 year ago in reply to Mateer Bhat

TI__Guru* 93670 points

Hi Mateer,

I am assuming you have a impedance controlled 75 and 50-ohm traces. MUTE_REF can be grounded or left floating.

Can you put scope on the output with infinite persistance to see what abnormality you observe?

Also, you did not mention what cable length you are using. Please check different cable length.

Regards,Nasser

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LMH0344: I have used the IC LMH0344 and observed the noise