Fig. 6.

Total harmonic distortion + Noise (a) and third order intermodulation distortion (IMD₃) (b) of the proposed instrument’s AFE (gain = 60 dB). (a) Taking into consideration that the available dynamic range of the AFE is from 1 μV peak to 2.3 mV peak, it is clear that the achieved THD + Noise is less than 0.3%. (b) The two tones applied to the AFE of the proposed instrument were f₁ = 4.9 Hz and f₂ = 5.1 Hz. The output power of a single fundamental tone (in dBm - red line in the graph) and the relative power of the IMD₃ products referenced to a single tone (blue circles) are plotted against the applied input power. The third-order intercept line (dashed blue line) is extended to intersect the extension of the fundamental output signal line (dashed red line). This intersection is termed the third order intercept point IP₃. The calculated IP₃ exhibits a relatively high value, which is desired, since the higher the IP₃ value the better the linearity of the amplifier and the weaker the output intermodulation products that will be generated at the amplifier’s output