LMK04616: About output 100 ohm termination.

Sho Ogane

Part Number: LMK04616

Hi all,

I would like to know about the position of 100 ohm terminate in HSDS => LVDS conversion output.
Datasheet P.32 HSDS section, the 100 ohm termination is situated at at Rx side from AC capling capacitor.

However the RFIC that my customer use recommend to situate Tx side face away from AC capling capacitor.
I attached the file.
Which point is best?

Best Regards,
Sho

over 6 years ago

0 Shawn Han over 6 years ago

TI__Genius 9920 points

Hi Sho,

You could put 100 Ohm load as below.

LMK04616 output has a pair of AC couple caps, then after 100 Ohm transmission line, install a 100 Ohm load before AC couple caps for RFIC.

Regards,

Shawn

0 Sho Ogane over 6 years ago in reply to Shawn Han

Genius 5575 points

Hi Shawn san

Thank you for your reply.

Sorry, is 0.1uF capacitor before 100 Ω trace required?
I think I need only 0.1uF between 100 ohm termination and RFIC.
is my understanding not correct?

Best Regards,
Sho

0 Shawn Han over 6 years ago in reply to Sho Ogane

TI__Genius 9920 points

Hi Sho san,
Both LMK04616 and RFIC do not like DC path on the 100 Ohm load, in case there is more DC current consumption on the load.
So it is better to have AC caps on both sides of 100 Ohm.

Regards,
Shawn

0 Sho Ogane over 6 years ago in reply to Shawn Han

Genius 5575 points

Thank you, I understood it.

0 Sho Ogane over 6 years ago in reply to Sho Ogane

Genius 5575 points

Hi Shawn san

Sorry, I would like you to check the connection circuit.
I attach the file, please check it.

Best Regards,
Sho

0 Shawn Han over 6 years ago in reply to Sho Ogane

TI__Genius 9920 points

Hi Sho san,

The circuits looks good.

Regards,

Shawn

0 Sho Ogane over 6 years ago in reply to Shawn Han

Genius 5575 points

Hi Shawn san

Thank you very much for your support.

Sorry, I have one more question.

This device is recommended AC-coupling output. If we want to make one pulse of SYSREF, I think AC-coupling is not good.
Can this device make 1 pulse signal of SYSREF?

Best Regards,
Sho

0 Shawn Han over 6 years ago in reply to Sho Ogane

TI__Genius 9920 points

Hi Sho san,
LMK0461x could output 1 pulse SYSREF signal by setting SYSREF pulse number( registers Register 0x140 ). It has to use DC path, so we should select proper output type to make sure receiver could accept LMK0461x's Voh and Vol.

Regards,
Shawn

0 Sho Ogane over 6 years ago in reply to Shawn Han

Genius 5575 points

Hi Shawn san

Thank you for your support.
Sorry for reply, I understood about SYSREF pulse.

I have one more question,
I would like to conversion HSDS signal to LVDS at CLKout and connect AC-coupling to RF IC because HSDS common mode voltage is different from LVDS voltage.
However receiver (RF IC) doesn't have internal bias circuit. So I think we need DC bias circuit between AC-coupling and RF IC input.

I attached RF IC's input required spec. Please tell me the recommend external DC bias circuit to connect RF IC.
I found the HSDS to LVDS circuit in datasheet P.32 Figure 31, but I think this is circuit dedicated to the receiver having internal bias circuit.

Best Regards,
Sho

0 Shawn Han over 6 years ago in reply to Sho Ogane

TI__Genius 9920 points

Hi Sho,

Let me understand your requirements.

You listed 2 kinds of clocks for RFIC.

1, REF_CLK_IN

It could be AC coupled, differential 0.3~2.0 Vpp (better to use < 1Vpp)

Is there an internal bias for this clock?

2, SYSREF & SYNCINB (LVDS)

They need DC coupled, differential 825~1675 Vpp

Where is the input Vcm range for the RFIC ?

Normally, LVDS receiver has a wide range for input Vcm.

Regards,

Shawn

0 Sho Ogane over 6 years ago in reply to Shawn Han

Genius 5575 points

Hi Shawn san

Thank you for your response.

Sorry I would like to know external bias circuit about SYSREF & SINCINB (LVDS) only.
There is internal bias for REF_CLK_IN, so I don't need external bias circuit.

I answer for your question below.
1, REF_CLK_IN
Is there an internal bias for this clock?
=>Yes, there is internal bias.

2, Where is the input Vcm range for the RFIC ?
=>825mV~1675mV. this voltage range is not differential Vpp.
I think RF IC is normal LVDS requirement spec.

Best Regards,
Sho

0 Shawn Han over 6 years ago in reply to Sho Ogane

TI__Genius 9920 points

Hi Sho,
If the RFIC SYSREF requests ViL to ViH on each line is 825mV~1675mV, then we need a careful calculation for this conversion circuits.
Reply you later.

Regards,
Shawn

0 Sho Ogane over 6 years ago in reply to Shawn Han

Genius 5575 points

Hi Shawn san

Thank you for confirming my question.
The requirement input spec of RF IC is normal LVDS requirement.
I am waiting your response.

Best Regards,
Sho

0 Sho Ogane over 6 years ago in reply to Sho Ogane

Genius 5575 points

HI Shawn san

I write the RF IC input spec below.
Vcm range = 825mV to 1675mV
Vpp =100mVpp

Best Regards,
Sho

0 Shawn Han over 6 years ago in reply to Sho Ogane

TI__Genius 9920 points

Hi Sho san,

Checked with designer, there is no method to DC couple from HSDS driver to this RFIC LVDS receiver.
So in this case, we have to select SYSREF mode in "External SYSREF request" or "Continuous SYSREF".
Then HSDS AC coupling to LVDS is fine.

Best Regards,
Shawn

0 Sho Ogane over 6 years ago in reply to Shawn Han

Genius 5575 points

Hi Shawn san

Thank you for your response.
OK, I suggest to adjust bias voltage with dividing resistor.

Best Regards,
Sho

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LMK04616: About output 100 ohm termination.