Input resistance in a pad

[ee484]

Hi, all~

I am wondering why some analog pads have input resistors associated with them.
What's the role of the resistors?

In analog I/O library from a foundary, typically has three types of analog pads, which are
1) Pad only
2) Pad with input resistor
3) Pad with diodes

I am wondering why we need such different types of pads.
For examples, why "Pad with diode" is not always used? I guess these diodes are for ESD. Don't we need ESD always? When do we have to consider to use pad only?? Or, with pad with input resistor? What are the pros/cons of using different PAD types?

Thanks,

Best,
B

 

[tfwee]

Pad with input resistor is used for ESD protection. Create a more resistance path so that it will not damage the gate of the transistor.

 

[ee484]

The pad associated with a resistor also has diodes in the schematic. Why do we need a resistor if we already have didoes? How is this resistor (series inbetween pad and terminal) used for ESD protection? Thanks

 

[pit1000]

pages 74-75 from A.Wang "On-Chip ESD Protection for Integrated Circuits"

 

[ashutoshdeenanath]

generaly there are two type of pads used in IC designing. input and output pads. generally input goes to the gate of mos and output comes from drain or source. to prevent gate from ESD we use diode protection simultaneously with resistor. if input or output does not goes to gate any one can use pad withot diode and resistor