|vlsitechnology.org /IR drop /example 1 /check|
We can check the result by using the strap widths and other chip specs to calculate the power that can be delivered. We use the procedure shown previously.
Step 1: Estimate Vcore using Ipad=50mA:
Step 2: Calculate the reference power supply conductance G:
|=||7 ⁄ (4 × 0.06) =||29.17 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.
|=||( 0.20 + 0.44 + 0.50 + 0.44 + 0.72 + 4.05 )|
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.
|=||2.226×(0.123+0.289) = 0.916W|
The iteration leads to the solution of Pnom=0.921W. This is slightly higher than the 0.9W of the example, which we expect because the power strap allocation percentage has been made slightly higher by the rounding up process.
|¹ p = 1−3.502/3.670|