LMH1983 / LVCMOS output VCXO

Sho Ogane

Other Parts Discussed in Thread: LMH1983

Hi all

I would like to know the following question.

My customer use LVCMOS output VCXO.
The VCXO used on the EVK may have 3.3V LVCOMS. So, 1.6V may be used.
Can you let me know why 1.2V bias is used instead of 1.6V?

Best Regards
Sho

over 8 years ago

0 Nasser Mohammadi over 8 years ago

TI__Guru* 93670 points

Hi Sho,

When using single ended LVCMOS, we should use XOin+ and bias XOin- to mid supply. CTS VCXO that is used on LMH1983 EVM, has minimum high level of 90% of VCC or 2.97V and maximum low level of 10% VDD or .33V. We can bias XOin- with 1.2V or 1.6V(mid supply) since in either case there is enough swing on XOin+ so we would get a logic high or low level. So either bias should work fine.

Regards,,nasser

0 Sho Ogane over 8 years ago in reply to Nasser Mohammadi

Genius 5575 points

Hi nasser san

Thank you for your reply.

Does this device have internal bias voltage?
Please check the attached file.
If so, I think XOin- could not be applied 1.6V.

Best Regards,
Shoquestion.pdf

0 Nasser Mohammadi over 8 years ago in reply to Sho Ogane

TI__Guru* 93670 points

Hi Sho-San,
Device does not have internal bias voltage. There is an internal comparator this way you can pull the un-used input to 1.2V or 1.6V.
Regards,,nasser

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LMH1983 / LVCMOS output VCXO