LMK1D1208EVM: Output Swing

Gruffalo

Intellectual 350 points

Part Number: LMK1D1208EVM
Other Parts Discussed in Thread: LMK1D1208, , LMKDB1108, LMK1D1208P

Dear Sir or Madam,

in the datasheet of the LMK1D1208 I see the following entry:

how can I achieve with the LMK1D1208 500mV output swing so 1 Vpp diff?

Is this even possible on the LMK1D1208 eval board?

3 months ago

0 Michael Srinivasan 3 months ago

TI__Genius 16981 points

Hello,

This is well beyond the specified LVDS standard output swing - this differential swing will not be achievable on the LMK1D1208EVM. It can roughly be achieved with the LMKDB1108.

Thanks,

Michael

0 Gruffalo 3 months ago in reply to Michael Srinivasan

Intellectual 350 points

Hi,

why is then the number given in the datasheet of the LMK1D1208?

400 mV 500 mV 650mV

Best,

Uros

0 Michael Srinivasan 3 months ago in reply to Gruffalo

TI__Genius 16981 points

Hello,

These are differential output swings, meaning that each individual output will have a swing between 200mV-325mV, and the differential swing is just 2 * the swing of one output.

Thanks,

Michael

0 Gruffalo 3 months ago in reply to Michael Srinivasan

Intellectual 350 points

ok thanks.

what does the AMP_SEL = 0 or 1 mean?

0 Gruffalo 3 months ago in reply to Michael Srinivasan

Intellectual 350 points

the LMKDB1108 can also only do 800mVpp diff or did I miss something in the datasheet?

0 Michael Srinivasan 3 months ago in reply to Gruffalo

TI__Genius 16981 points

Hello,

The LMK1D1208 does not feature an AMP_SEL pin. That is only a feature in the LMK1D1208P - it allows you to select a differential output swing of either 350mV or 500mV.

The LMKDB can go all the way up to 975mV.

Thanks,

Michael

0 Gruffalo 3 months ago in reply to Michael Srinivasan

Intellectual 350 points

Hi Michael,

sorry for dwelling on this matter but I have to clarify this.

I am measuring the LMK1D1208 with an active, calibrated diff. probe and I can measure 700mVpp diff. (overshoot removed). According to your response above it can only do 350mV. Now, this 350mV is open to some interpretation because I think to compare it to the measurement I have to multiply it by 2. LVDS is +-175mV amplitude on P and N. This is 350mVpp on P and N. Differential is 700mVpp. So from where I stand , the measured value fits the calculated value.

If the above is the case and I did not make any mistake in process, the 500mV in the datasheet would actually mean 1Vpp measured.

and following these lines the 975mV would mean 1950mVpp measured.

or?

Best

+1 Michael Srinivasan 3 months ago in reply to Gruffalo

TI__Genius 16981 points

Hello,

There was some confusion on my part - the LVDS swing specs from the datasheet above are the magnitude - meaning that the differential p2p voltage can be as high as 900mV. And you are correct, the 500mV magnitude would correspond to a differential p2p voltage of 1V. My apologies for the confusion.

Thanks,

Michael

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LMK1D1208EVM: Output Swing