|vlsitechnology.org /IR drop /12% power straps|
Example Calculation of Core Power with 6LM, Different Resistivities and Widths and 15% of Metal‑2 allocated to Power
An alternative to calculating the supply strap width given the core power consumption is to calculate the core power given the width of the supply straps. We will use a power strap allocation percentage p=15% with the power strap ratios and metal resistivities of the previous example to find the maximum core power.
Step 1: Estimate Vcore using Ipad=50mA:
Step 2: Calculate the reference power supply conductance G:
|=||7 ⁄ (4 × 0.07) =||25 mhos|
Step 3 is to set out the values of kan, kwn, kcn and mn for each metal layer, and use these to calculate the value of L.
|=||( 0.24 + 0.8 + 0.4 + 0.8 + 0.4 + 5.6 )|
Step 4: Calculate Pnom. Pnom depends on the value of Ipad which we don't know, so we start with Ipad=50mA which gives us Vcore, then Pnom and a new value of Ipad. We use a spreadsheet to iterate to the solution. The yellow squares mark user input and the pink squares are calculated values. The first estimate for Pnom is shown below.
|=||1.445×(0.173+1.236) = 2.036W|
The iteration leads to the solution of Pnom=2.007W. This is slightly higher than the 2W of the previous example, which we expect because the power strap allocation percentage is slightly higher at 15% instead of 14.92%.
|¹ the width (which is probably what is measured) is p×kw, or 80% of this value|