This document presents an apparatus comprising: a first signal line configured to couple signals from a first skin electrode to a first input of a differential amplifier comprised as a front-stage in a signal detection circuitry for measurement of biometric signals sensed by the first skin electrode； a second signal line configured to couple signals from a second skin electrode, different from the first skin electrode, to a second input of the differential amplifier of the signal detection circuitry for measurement of biometric signals sensed by the second skin electrode； and an impedance circuitry coupled between the first signal line and the second signal line in order to tune input impedance of the differential amplifier, wherein impedance of the impedance circuitry is higher on a first frequency band covering a frequency band of the measured biometric signals than on a second frequency band not covering the frequency band of the measured biometric signals.
