Amplifiers With and Without Enhanced Electromagnetic Interference (EMI) Filtering

With the rapid expansion of wireless capabilities that the electronics industry has seen over the years, the presence of Electromagnetic Interference (EMI) is becoming a bigger concern for system designers. This error source is nearly impossible to predict; hence, it is extremely difficult to bulletproof a design against its adverse effects.

So, What Is EMI?

EMI is a disturbance that can affect any electrical system either through radiated electromagnetic energy or through conducted electromagnetic energy. Radiated EMI can be generated from a variety of sources outside of the electrical system, such as mobile phones, wireless gaming controllers, wireless headsets, and radio transmitters. Conducted EMI can also come from a variety of sources. One common source is radiated EMI that couples onto the traces and wires within the electrical system in question. Conducted EMI may also be generated within the system itself, such as from a switching power supply.

EMI affects amplifier circuits by causing a shift in the offset voltage which causes performance degradation. For example, in Figure 1, a simple sine wave is passed through an amplifier circuit. However, the presence of high-frequency interference, in this case from a cell phone, causes a voltage shift in the output waveform.

Figure 1: Standard Amplifier Without EMI Filtering

By implementing a passive low pass filter external to the op amp input pins, the effects of this high-frequency interference can be reduced, as shown in Figure 2.

Figure 2: Standard Amplifier with External Filtering

Although the performance is better with an external filter, there is still substantial degradation in the output signal. Amplifier manufacturers have taken steps to minimize the effects of these unwanted signals. For example, Microchip Technology’s MCP642x operational amplifier features integrated second-order filters on the input pins to enhance EMI rejection. By integrating the filters directly on-chip, the adverse effects of EMI can be greatly reduced. This result is shown in Figure 3.

Figure 3: MCP642x Amplifier Without External Filtering

Microchip continues to expand its portfolio of amplifiers featuring enhanced EMI rejection. Table 1 highlights the list of amplifiers with on-chip EMI filtering at the time of publication for this page. We have a parameter called “EMI Protection” on the amplifier parametric tables that can be found on the Microchip website, which is either a Yes or No. You could filter on this parameter to find all the devices with on-chip EMI filtering within that product section.

Table 1: List of Microchip Amplifiers Featuring Enhanced EMI Rejection
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