Thread: Overshoot and undershoot

Hi all,

What is the causes of overshoot and undershoot for an inverter?
Does using G device produces smaller overshoot and undershoot compared to LP device?

Thanks.

Regards,
Lip-Kai

I would say the parasitic/load capacitor. The load capacitor is a very important factor. Just look at its transfer function whose poles are determined by the capacitor.

In J. Rabaey, A. Chandrakasan and B. Nikolic, “Digital Integrated Circuits: A
Design Perspective”, second edition, Prentice Hall, NJ, 2003

chapter 5, pag197

"...the overshoots on the simulated output signals. These are caused by the gate-drain capacitances of the inverter transistors, which couple the steep voltage step at the input node directly to the output before the transistors can even start to react to the changes at the input. These overshoots clearly have a negative impact on the performance of the gate, and explain why the simulated delays are larger than the estimations."

http://en.wikipedia.org/wiki/Overshoot
http://www.merriam-webster.com/dictionary/steep

In electronics, overshoot refers to the transitory values of any parameter that exceeds its final (steady state) value during its transition from one value to another. An important application of the term is to the output signal of an amplifier.[3]

Usage: Overshoot occurs when the transitory values exceed final value. When they are lower than the final value, the phenomenon is called "undershoot" or "negative overshoot".




Undershoot -->voltage below VSS

Overshoot-->voltage above VDD


How do we enable voltages beyond VSS, VDD, result of switching them to output?

Nonlinear Behaviour and transient (not driven, controlled by input)


Voltage-->energy/unit of charge going to reference (lower potencial in the circuit)

unit of charge=1>0C -->positive charge

Conclusion:

CLEARED because naive ERRORs

these overshoot and undershoots are bcoz of chargin and discharging of parasitic capacitors. actually when a step input is applied on an inverter the parasitic RC combination work as an integrator and convert it into a sharpe peak which looks like a over and under shoot.