How does a second order filter affect attenuation?

The capacitor (in a second order filter configuration) determines the attenuating behavior of the filter at frequencies above resonance (Figure 6), and with very little capacitance, the filter response exhibits the rapid decrease of attenuation due to the inductor response.

How much attenuation does a 3rd-harmonic filter provide?

At 6 MHz input, the 3rd falls at 18 MHz and will see 3dB attenuation from the harmonic power present at VI. As this input frequency moves up to 10 MHz, this 2ndorder filter provides 12.4dB attenuation for the 3rd-harmonic falling at 30 MHz.

What is the level of attenuation in a capacitor?

Further attenuation in a capacitor is prevented by inductance and series resistance in the capacitor elements. All attenuation curves usually start leveling out at approximately 70 – 80 dB.

What are the disadvantages of a feedthrough capacitor?

Feedthrough capacitors are able to work at higher frequencies and are more broadband than standard capacitors. The disadvantage of feedthrough capacitors are higher cost and added impedance to the circuit of 0.2 to 0.6 ohms. In low voltage applications this could be an important consideration. Figure 6.

Does R2 cost a DC and AC attenuation?

If the final design requires a DC blocking cap to be inserted at R1, then R2 becomes the DC biasing resistor at the input of the ADC. For the circuit of Figure 1, R2 does cost a DC and AC attenuation in the signal from VI to VO – it is intended that the designs using an R2 will pick values for R1 and R2 where this attenuation is < 10%.

Does a purely differential capacitor filter a common-mode signal?

The input common-mode signal still sees a common-mode load through R 2, but now receives no filtering effect due to C. The purely differential capacitor now acts only to filter the differential signal and is transparent to any common-mode AC signal.