As explained on an earlier slide showing the basic MOSFET structure, the input buffer level shifts the digital inputs and applies signal to the drivers which are responsible for turning on and off the switch channels. As with any digital signal, there are four important specifications known as trigger levels that must be observed to ensure correct operation of the switch. Two of these specifications are V(ih) and V(il). V(ih) is the minimum voltage level required by the input buffer to recognize a logic high. For a logic low, V(il) is the maximum voltage level that can be applied to the input buffer to ensure a logic low, while 0V is the minimum acceptable voltage. In order to meet the V(il) and V(ih) levels of the switch, it is important that the designer considers the output voltage levels of the device driving/controlling the switch. The output levels of that preceding device driving the switch are known as V(oh) and V(ol). V(oh) is the minimum voltage level that the preceding device will output as a logic high. This level must exceed the V(ih) requirement of the switch. On the other-hand, V(ol) is the maximum level that the preceding device will output as a logic low, and this voltage level must be less than the V(il) requirements of the switch.