Low-frequency analog and digital electronic circuits are susceptible to electromagnetic interference in the radiofrequency (RF) range. This disturbance is produced when the coupled RF signal is rectified by the nonlinear behavior of the semiconductors used in the small-signal analog input stage of the electronic system. Circuits based on operational amplifiers are usually employed for such input stages. These circuits present an amplitude modulation demodulation produced by the nonlinearity of internal transistors. Such a phenomenon generates demodulated signals in the low-frequency range. In this paper, this effect is suppressed by combining the conventional printed circuit board layout with complementary split-ring resonators (CSRRs). CSRRs are constitutive elements for the synthesis of metamaterials with negative effective permittivity, which are mainly excited to the host line by means of electric coupling. Electromagnetic simulations and experimental results show an effective rejection of the undesired RF demodulation effect with no extra cost in terms of the device area or manufacturing process.