Why using Dual input PAD

[ljy4468]

Hi all

I've a question about PAD.
I;ve heard about that.
For input pad, (Clock input or signal input)

It's recommended using two pads.
That is, same node with using two pads.

Then what's the merit?

Thanks in advance

 

[rfasic]

Who recommends this (where)??

Are you sure they are talking about the digital pads (those containing buffers/inverters).
I would say that it could be an advantage for the analog pads when they are used for supply (VDD or GND) to reduce the inductance. Or for signals carrying very large currents.

 

[ljy4468]

Oh...I say analog pads..
like input signal in ADC.

not digital, sorry

Then, using double pads to reduce inductance..
That's ok.
But I want to know why small inductance when using double pads.

Please tell me in detail
thanks

 

[muldersun]

You can calculate using following method:
v=L*dI/dt,
So, when dI/dt is large enough, the delta V is not neglected.

 

[advaita]

Then, using double pads to reduce inductance..
But I want to know why small inductance when using double pads.

Hi

I think you mean double bonding to pads. That is : they bring two parallel bond wires from the package to the PAD instead on just one. Thus, the inductances come in parallel.

 

[kallen3]

Hi RFASIC~~~

I've a question about your opinion.
Analog is ok but digital is not??
Doesn't it recommended using two pads like Clock input pin???

I'm confused

 

[pixel]

It is not good idea to make two clock outputs because of mutual inductance between other pins. Shortly EMC would be doubled.

At the output of the chip voltage can be stabilized using decoupling capacitor, but the real problem is voltage drop on the inductance (proportional to current change rate) between pad and output capacitance, which results that voltage inside the chip is not stabilized.
This problem could be solved by two gnd outputs where one has higher and other much lower current (some sensitive analog circuit where you need stable gnd). The point is that voltage drop at the low current lead is small which means that gnd inside circuit is good stabilized.

 

[kallen3]

OK. pixel~

I understood your text.
Thanks.

But still I want to know about clock INPUT pin.