Conventional wisdom says smaller is better where battery operated wireless systems are concerned. Higher silicon integration and smaller package technol- ogy have shrunk system electronics to the point where system size is dictated by the size of the battery pack and user interface (keyboard and display).
Reducing the size of the user interface in consumer devices, such as, cellular phones and pagers is largely an ergonomic issue. On the other hand, reducing battery size means reducing the number (or size) of the cells in the pack, or changing to a higher energy density battery chemistry, such as, Lithium-Ion (Li-Ion). Both options result in battery size reduction at the expense of lower battery energy capacity and/or lower terminal voltage. Reduced battery terminal voltage is one factor hastening the departure from 5V to 3V (and lower) system supplies.
Microchip Technology offers linear circuit devices that combine op amps, comparators and voltage references into a single package. These devices can operate from supply voltages as low as 1.4V, and their operating currents can be as low as 600 nA depending on the device. These products are available in a variety of packages ranging from a 5-pin SC-70 to a 16-pin QSOP.