Most modern computers are digital. But they function in a world of continuously varying analog input such as sound, light, and heat. Every “digital” consumer product, from appliances and cell phones to music players, has analog ICs feeding its digital heart. Analog ICs typically enjoy a far longer useful life than digital devices. While the circuit designs have been refined and the cost of the chips reduced as manufacturing processes improved, the basic functions of many analog devices continue to be useful in new electronic products after more than 40 years.