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Hello, and welcome to the switches and multiplexers series on basics of analog signal switches offered by Texas Instruments. In this video, we will have a short discussion on input logic levels of switches and multiplexers, as well as output logic levels. We will cover the logic thresholds V OH, V OL, V IH, and V IL, and discuss how to simplify system design with 1.8-volt logic-compatible muxes.

The control logic of your switch or mux is likely being driven by an open drain or push-pull driver. Based on the supply voltage and specifications of your driver, the output signals that are driving the switch's control logic have designated thresholds to indicate a logic 1, high, or a logic 0, low.

These thresholds are called V OH-- Voltage Output High-- and V OL-- Voltage Output Low-- respectively. An output voltage above the V OH threshold is considered a high by the driver, and a voltage below the V OL threshold is considered a low by the driver.

Similarly, a switch's control inputs must have internal thresholds to indicate if an input signal is high or low. These thresholds are called V IH-- Voltage Input High-- and V IL-- Voltage Input Low. An input voltage above the V IH threshold is considered a high by the switch. And a voltage below the V IL threshold is considered a low by the switch. Based on the input signal, the internal logic controls which internal signal paths are on, off, or selected.

When designing your system, it is important to consider both the output thresholds of your driver and the input thresholds of your switch. To ensure that the driver's output signal will effectively control the switch, you must be certain that the V OH is above the V IH and that the V OL is below the V IL.

There are different standards of logic thresholds, depending on design process and voltage node. It is important to understand which logic thresholds are compatible with each other when designing a system with control logic. In some cases, your driver's V OH and V OL levels may not be aligned with your switch's V IH and V IL levels.

For example, if your driver is operating at 1.8 volt supply and your switch is not compatible with 1.8-volt logic levels at the necessary supply voltage, the output high threshold may not be high enough to cross the input threshold and the switch will enter an undefined state. In this case, a discrete or integrated translator is needed to translate the 1.8-volt control signal from the driver to the respective V IH and V IL levels of the switch.

In this example, you can avoid using a level translator by choosing a switch with 1.8-volt logic capability. These switches have internal translators ensuring that the control input thresholds remain fixed, regardless of supply voltage. This allows you to simplify design and save system size and cost.

The V IH and V IL levels of each switch or mux can be found in the Recommended Operating Conditions or Electrical Characteristics section of the datasheet. Note that V OH and V OL levels are not in a switch's datasheet, as these parameters are specific to the external component driving the control signal. In a device without 1.8-volt control inputs, the V IH and V IL levels may be defined relative to the supply voltage.

In a device with 1.8-volt control inputs, the V IH and V IL levels will be fixed to align with the CMOS 1.8-volt logic standard, regardless of the supply voltage.

To find a switch with 1.8-volt-compatible control inputs, filter by features in the analog switches and multiplexers product search tool, found in the switches and multiplexers product tree on ti.com.

To ensure logic signal compatibility, V OH of control logic driver must be higher than V IH of the switch. V OL of the control logic driver must be lower than the V IL of the switch. Switches in muxes with 1.8-volt logic eliminate need for external logic-level translators. To learn more about 1.8-volt logic switches, see the app note, Simplifying Design with 1.8-volt Logic Muxes and Switches.

Thank you for watching this switches and multiplexers TI Precision Labs video about input and output control logic levels. To find more switches and multiplexers, technical resources, and search products, visit ti.com/switches.