Apple Inc.
Analog switches immune to power sequence

Abstract:

A system and method for efficiently receiving analog input signals. In various embodiments, a functional unit includes a switch in its interface logic. The switch receives an analog input signal, and when enabled, conveys the received input signal as an analog output signal. The switch is enabled when the received enable signal is asserted. However, when the power supply voltage is at a logic low level, an output n-type device is disabled while an output p-type device is enabled. A guard p-type device serially connected with the output p-type device is disabled by other devices used to control the guard p-type device. The control devices also ensure that the body terminals of the guard p-type device and other p-type devices receive a logic high level regardless of the power supply value, which prevents forward bias currents in parasitic diodes of the p-type devices.