A method for producing a chip is disclosed. A first step of the method may include fabricating the chip only up to and including a first metal layer such that a core region of the chip has an array of cells, each of the cells having a plurality of transistors. A second step generally involves designing a plurality of upper metal layers above the first metal layer in response to a custom design created after the first fabricating has started, the upper metal layers interconnecting a plurality of the cells to form (i) a mixed-signal module and (ii) a digital module, the mixed signal module generating at least one analog signal and at least one digital signal. In a third step, the method may include fabricating the chip to add the upper metal layers.