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12 DESIGN007 MAGAZINE I NOVEMBER 2025 tional capacitance of the plane isn't significantly improving the noise voltage, as its contributions are outside of the calculated effective area based on the rise and fall times of the current sink. Experiment 3: Increasing Dk and Changing Layer Spacing Now, let's increase the dielectric constant of the material to 20, which is considerably larger. The simulation resulted in a peak noise voltage of 72.3 mV, which is slightly improved over the previous experiment (87.1 mV). Simply looking at Equation 1 for capacitance indicates that we might expect to see a larger difference in noise voltage when using a higher dielectric constant. However, the new effective decoupling radius using a dielectric con- stant of 20 is calculated to be 0.67 in. This radius results in an effective area of only 1.41 in 2 , which by comparison, is much smaller than 6.60 in 2 as it was in the original experiment. By increasing the dielectric constant, we shrink the effective decoupling radius, and thus the plane area that the current sink can actually use. The effective capacitance from the original dielectric constant (4.3) is approximately 2.13 nF, whereas the F i g u re 3 : T h e re s u l t s of t h e b a s e l i n e s i m u l at i o n c o n n e ct i n g t h e V R M a n d c u r re nt s i n k to L aye r 2 ( VC C1 _ 5 ) . Pe a k n o i s e vo l t a g e i s 91 .4 m V at t h e c u r re nt s i n k . ▼ F i g u re 4 : T h e re s u l t s of E x p e r i m e nt 2 . T h e a re a of t h e P C B ( 6 4 i n 2 ) i s n ow m u c h l a rg e r t h a n t h e c a l - c u l ate d ef fe ct i ve a re a ( 6.6 0 i n 2 ) , yet t h e n o i s e vo l t a g e ( 87.1 m V ) i s a l m o st u n af fe cte d f ro m t h e p rev i o u s s i m u l at i o n ( 91 .4 m V ) . ▼ new capacitance formed by increasing the dielec- tric constant to 20 is also calculated as 2.13 nF. The results of the simulation are shown in Figure 5. F i g u re 5 : T h e re s u l t s of t h e s i m u l at i o n fo r E x p e r i - m e nt 3 . T h e d i e l e ct r i c c o n st a nt wa s i n c re a s e d to 2 0 fo r a l l l aye rs . T h e n o i s e vo l t a g e at t h e c u r re nt s i n k h a s o n l y d ro p p e d 1 4. 8 m V f ro m t h e s a m e s et- u p w i t h a n o r m a l d i e l e ct r i c c o n st a nt of 4.3 . ▼