Device-Specific Power Delivery Network (PDN) Tool 2.0 User Guide

ID 683293
Date 8/24/2021
Public
Document Table of Contents

1.3.3.2. Optimizing the Decap Count

Since the tool is a code-based spreadsheet, it keeps adding up the number of decoupling capacitors until ZPDN satisfies ZTARGET up to FEFFECTIVE. The PDN tool has a 301ea maximum decap count.
  1. Change the Decoupling mode from Auto to Manual.

    There can be a ±5% variation on ZEFF impedance when doing decoupling caps optimization. This impedance variation can relate to fabrication tolerance.

    Figure 35. Manual Decoupling Results Summary - Pre-Optimization
  2. Observing the impedance plot carefully, optimize the number of each capacitor.
    Figure 36. Manual Decoupling Results Summary - Post-Optimization, Round 1After optimizing manually, 301ea decaps are dramatically reduced to 124ea while maintaining a similar ZPDN profile (the red curve) under the same ZTARGET.
    Figure 37. Manual Decoupling Results Summary - Post-Optimization Results, Round 1A small amount of violation at different frequencies can reduce the number of decaps. Before and after results are shown below.