CDCLVP111-SP: DC-Coupled LVCMOS Input to CDCLVP111-SP

Hello Chong Kim,

I will let Jennifer comment on this.

Best,

Aaron Black

Hi Chong,

What is the oscillator part number and what are your VIH/VIL values? This information is needed for me to determine if the VCM is violated.

Regards,

Jennifer

The oscillator is a +1.8V LVCMOS so we can assume VIH = 1.8V and VIL = 0 and Vth would be set to 0.9V, 1/2VCC.

Thanks,

Chong

Chong, 

The recommended supply voltage is 2.5V or 3.3V. Are you using 1.8V as your supply?

Regards,

Jennifer

Yes, I am using 1.8V supply.  If the Vth is 0.9V, the VID would also be 0.9v which satisfies the requirement. My question was what about the Vcm?  Is there an issue with Vth being 0.9V. 

Thanks,

Chong

Let me be clear: the power supply for CDCLVP111 is +2.5V but the oscillator is +1.8V.

Thanks.

Hello Chong Kim,

The Vcm should be set based on CDCLVP111 Vcc not Oscillator Vcc. If you are trying to utilize 0.9V (1.8V/2) of Vcm this does not meet requirements.

The 0.9V is for Vth, not for Vcm.  The question was how to interface a +1.8V LVCMOS signal to CDCLVP111?  Aside from setting Vth = 0.9V, are there any other issues that need to concerned with?  Does Vcm even matter for interfacing a LVCMOS signal to CDCLVP111?

Hi Chong,
The VCM must be within the specified datasheet range when the inputs are DC coupled. You'd have to change the external biasing circuitry to match the datasheet requirements. If the inputs are AC coupled, then the VCM does not matter.

Regards,

Jennifer

See below: If the LVCMOS is +1.8V and Vth = 0.9V, what other issues do you see?