1. In, Out , InOut , Gnd , Vdd, Source follower
I/O PADS
In, Out , InOut , Gnd , Vdd,
Source follower

2. Bidirectional Pad - Digital Component.
Operates as Pad_in or Pad_out:
EO high => pad out.
EO low => pad in.

3. Pad Layout
DataIn OE
DataOut
DataInBuf
DataInUnBuf

4. Pad In DC Analysis
DataInB, after one inverter, has less gain than dataIn

5. Max frequency 100Mhz VinBar Vin Vpad Dx = 4.11nsec (>80%*5=4nsec)
Cursers mark position where output exceed 80% of max input value

6. Pad out Dc Analysis Response similar to dataIn.
Explanation: It has two levels of amplifying, as the dataIn node.

7. Max frequency 30Mhz with 10pF capacitor as load
Vpad
DataOut
Dx = 14.06nsec (> 80%*17=13.6nsec)
Cursors mark position where output exceed 80% of max input value

8. Sf with no ideal current source
Function: Pad follows Signal, with DC offset.

9. SF Layout
Vss
Vdd
Signal

10. SF behavior (with the pmos as current source)
Current source values -190 to -150 uA
0<Vin<4 volt, the SF follow the input with 0.85 V offset.
3.5V
4 V

11. Let’s have a closer look
Vpad – Vsignal = 0.85 constant when 0 < Vsignal <= 4

12. Slew Rate of the SF Vsignal Vpad Vpad-Vsignal
Vsignal = ramp from 0 to 5v in 1usec
The SF still follow the step in the range of 0<VSignal<4volt

13. Pad I/O With ESD D2 D1
Two diodes are placed to protect the chip, and are normally at reverse charge.
When signal exceeds 5+Vb volts, then D2 is forward biased and discharges the excess voltage.
When signal is below –Vb, then a similar discharging process occurs through D1.

14. PadIOEsd Layout signal Diode 2  D2 in scehematic
Diode 1 D1 in schematic
signal

15. Modeling the Pad
The modeling was done by attaching a capacitor, and a resistor, to the pad. They reperesent the capacitance and resistance of three main models: Human, machine, and package.
To run simulation, an initial voltage was initialized on the model.

16. Human model.
R=1.5kΩ, C=100pF,
Initial Voltage = 2kV

17. Machine Model.
R=25Ω, C=200pF,
Initial Voltage = 200V

18. Package Model
R=1Ω, C=1.5pF,
Initial Voltage = 2kV