JAJSE79C June 2017 – October 2018 OPA1692
The electromagnetic interference (EMI) rejection ratio, or EMIRR, describes the EMI immunity of operational amplifiers. An adverse effect that is common to many op amps is a change in the offset voltage as a result of RF signal rectification. An op amp that is more efficient at rejecting this change in offset as a result of EMI has a higher EMIRR and is quantified by a decibel value. Measuring EMIRR can be performed in many ways, but this section provides the EMIRR IN+, which specifically describes the EMIRR performance when the RF signal is applied to the noninverting input pin of the op amp. In general, only the noninverting input is tested for EMIRR for the following three reasons:
High-frequency signals conducted or radiated to any pin of the operational amplifier result in adverse effects, as the amplifier does not have sufficient loop gain to correct for signals with spectral content outside its bandwidth. Conducted or radiated EMI on inputs, power supply, or output may result in unexpected DC offsets, transient voltages, or other unknown behavior. Take care to properly shield and isolate sensitive analog nodes from noisy radio signals and digital clocks and interfaces.
The EMIRR IN+ of the OPA169x amplifiers is plotted versus frequency as shown in Figure 58. If available, any dual and quad op amp device versions have nearly similar EMIRR IN+ performance. The OPA169x unity-gain bandwidth is 5.1 MHz. EMIRR performance below this frequency denotes interfering signals that fall within the op amp bandwidth.See EMI Rejection Ratio of Operational Amplifiers, available for download from www.ti.com.
Table 1 lists the EMIRR IN+ values for the OPA169x at particular frequencies commonly encountered in real-world applications. Applications listed in Table 1 may be centered on or operated near the particular frequency shown. This information may be of special interest to designers working with these types of applications, or working in other fields likely to encounter RF interference from broad sources, such as the industrial, scientific, and medical (ISM) radio band.
|FREQUENCY||APPLICATION OR ALLOCATION||EMIRR IN+|
|400 MHz||Mobile radio, mobile satellite, space operation, weather, radar, ultra-high frequency (UHF) applications||45.9 dB|
|900 MHz||Global system for mobile communications (GSM) applications, radio communication, navigation, GPS (to 1.6 GHz), GSM, aeronautical mobile, UHF applications||50.2 dB|
|1.8 GHz||GSM applications, mobile personal communications, broadband, satellite, L-band (1 GHz to 2 GHz)||70.7 dB|
|2.4 GHz||802.11b, 802.11g, 802.11n, Bluetooth®, mobile personal communications, industrial, scientific and medical (ISM) radio band, amateur radio and satellite, S-band (2 GHz to 4 GHz)||76.1 dB|
|3.6 GHz||Radiolocation, aero communication and navigation, satellite, mobile, S-band||94.1 dB|
|5 GHz||802.11a, 802.11n, aero communication and navigation, mobile communication, space and satellite operation, C-band (4 GHz to 8 GHz)||104.5 dB|