# Huge on-die capacitor

The schematic of the LM113 precision reference shows a 75pF capacitor integrated in the IC. Looks huge to me. What's the limit when integrating capacitor on-die?

• I never thought to associate '75pF' with 'huge', but then again, I come from a switching power background where thousands of microfarads are sometimes considered 'not enough'. ;) – Adam Lawrence Jun 17 '11 at 12:32
• @Madmanguruman - I see what you mean. I can imagine very-high-power engineers thinking how you could possibly care about a single $\mu$A, too. :-) – stevenvh Jun 17 '11 at 12:37
• Are you positive it's on the die, and not just in the package? – drxzcl Jun 17 '11 at 22:47
• @Ranieri - it's most probably on the die. The other solution would be expensive, wiring-wise, especially since there seems to be another 30pF cap in the schematic. My guesstimate was that it would need only $0.1mm^2$. – stevenvh Jun 18 '11 at 6:00

The limit is just what you're prepared to pay. In a 0.13 $\mu$ process it would be a shame to waste all this space on a cap; you could place probably 10 000 transistors there.
Assuming a separation of 0.1 $\mu$ and a dielectric constant of 10 a 75 pF capacitor will be around 0.3 mm x 0.3 mm. Not that bad after all.