7.3.6 EMI Susceptibility and Input Filtering

Operational amplifiers vary with regard to the susceptibility of the device to electromagnetic interference (EMI). If conducted EMI enters the op amp, the dc offset observed at the amplifier output can shift from the nominal value while EMI is present. This shift is a result of signal rectification associated with the internal semiconductor junctions. While all op amp pin functions can be affected by EMI, the signal input pins are likely to be the most susceptible. The TLV600x-Q1 family incorporates an internal input low-pass filter that reduces the amplifiers response to EMI. This filter provides common-mode and differential mode filtering. The filter is designed for a cutoff frequency of approximately 35 MHz (–3 dB) with a rolloff of 20 dB per decade.

Texas Instruments developed the ability to accurately measure and quantify the immunity of an operational amplifier over a broad frequency spectrum extending from 10 MHz to 6 GHz. The EMI rejection ratio (EMIRR) metric allows op amps to be directly compared by the EMI immunity. Figure 18 shows the results of this testing on the TLV600x-Q1 family. EMI Rejection Ratio of Operational Amplifiers shows detailed information, and is available for download from www.ti.com.