When the IR energy is emitted from the source, it can bounce off other objects and make its way back into the detector. This phenomena is called multipath and can be added to the detected signal. The IR emitter is an important consideration in proximity designs. There are several parameters associated with the IR emitter that need to be evaluated for these systems. Many proximity measurement systems are found in battery powered applications so power consumption is important. Choosing an IR emitter (like an LED) with a high electrical to optical efficiency would provide better battery performance by allowing lower currents to be used while hitting the range requirements of the application. The emission angle of the LED is also important and also contributes to the range of the system along with the size of the target and the area around the device that is to be monitored. All emitters have a certain range of wavelengths that they output. The peak output should correspond to the peak sensitivity of the detector. Selecting components that have the peak wavelengths the same provides the greatest efficiency of the system. For example, having an emitter with a peak output of 880nm would not be as good a choice as having an emitter that has a peak output of 850nm when using the Silicon Labs Si1120 that has its highest sensitivity at 850nm. In addition to the emitter’s peak wavelength, the effects associated with the aging of the emitter should also be considered as intensity and other parameters may change over time. Ambient light will be covered in another section of this PTM so it will not covered right now other than to say it can affect the overall measurement since background light sources contain wavelengths in the IR spectrum. The mechanical design of the complete assembly plays an important role in proximity sensing applications. The more isolation that can be provided by the mechanical assembly the more dynamic range that will be available to the sensor. For example, if the emitter is completely isolated from the receiver, then all of the signal received is from the reflected object and there is minimal offset in the reading. If to much light is allowed to enter the cavity where the detector is, then the emitter energy can be received without being reflected by any objects. This will increase the measurement offset and reduce the dynamic range available for the reflected energy.