Chapter 9. Transient Currents and PDN Voltage Noise
9.1 What’s So Important About the Transient Current?
The voltage noise generated on the core power distribution network depends strongly on the specific transient current flowing between the Vdd and Vss rails and the PDN impedance. If the PDN current draw of the die were constant, the only consideration in PDN design would be the PDN’s DC resistance. This quality is referred to as the IR drop in the PDN.
Because many regulators have an external sense line that is used as the source of feedback voltage to regulate the output voltage, attaching the sense lines in close electrical proximity to the die pads ensures the constant DC voltage is close to the intended voltage. This allows for a trivial ...