Power supply transient response considerations for testing portable wireless devices

The designers of today's portable, battery-powered electronic equipment, such as cellular telephones, pagers, two-way radios, personal digital assistants, and other communication devices, are constantly striving to provide greater functionality and higher speed in a smaller package. At the same time, they want to offer longer operating periods between recharges. As desirable as these capabilities are from the consumer's perspective, they pose new challenges for the device manufacturer's production test engineers. For example, the trend toward lower voltage circuitry and allowing longer operation between recharges is constantly forcing a decrease in the minimum battery voltage level at which the device will operate before automatically turning itself off to prevent damage. With power levels remaining the same or increasing, the operating currents are becoming larger. Also, to conserve power, today's portable electronics typically operate in pulse fashion; in other words, the device will enter "idle" mode when not being used, quickly switch into "operate" mode to perform a function, then go back to idle mode when no longer immediately needed. For example, a cellular phone that is not being used will be in stand-by mode, then switch itself on to transmit, then switch back to standby. During these transitions from one mode to another, it is not uncommon for the load on the battery to change from tens of milliamps to several amps in just 20 to 50 microseconds. This means that test systems must include power supplies capable of responding quickly to transient load changes.