Maximum output clock frequency in 0.35 µm

[Junus2012]

Hello,
I am using the 0.35 µm CMOS technology,
I designed for my purposes some simple clock generator circuit using the inverter ring oscillator. The circuit generates high clock frequency signal (120 MHz),
I am wondering if chip pad can respond to this frequency or not, where can I find such information.

Upon your experience, what is the maximum clock frequency I can safely use to drive an output pin.

For sure I need to design buffer stage to drive the pad, how much I should consider the PAD load capacitor?

Thank you
Best Regards

 

[AMS012]

Pad will usually consist of metal layers like the top metal layer and the redistribution layer in a given technology. So, you should be able to open the layout of the pad, and depending on the metals present in the pad and its dimensions, you should be able to get a rough estimate for the pad capacitance.

 

[dick_freebird]

This is all about things like output buffer drive
strength and spec load range, and output signal
format and transmission lines.

In my experience a 3.3V CMOS buffer will be
getting soft about 50MHz and may fail to go
full rail-rail before 100MHz, with a ~10mA
buffer and 50pF load (as is often the spec).

Beyond this you want to be using controlled
impedance low swing standards like LVDS or
PECL.

 

[Junus2012]

Thank you friends for your help,

do you have suggestion for the buffer design,

I am designing buffer based on inverters chain, still suffering to drive 10 pF at fck more than 20 MHz, unless if I increase the buffer chain considerably, may be there is better buffer option?

thanks

 

[martinnl]

When you say it suffers when driving a 20 MHz signal. What do you mean? Are the edges too slow? Doesn't it even reach full amplitude?

A common mistake I see is that people expect the rise and fall time to be close to non existing but you should consider what you need in your application.

 

[Junus2012]

Thank you martin
the signal start to slew, then it will be a problem for the measurement if I connect that pin to external device (like pin for microcontroller) or oscilloscope prob