reference point for the gain stages the resistor r5 is also coupled to ground the output of the multiplexer is also coupled to a first terminal of capacitor c2 the second terminal of the capacitor c2 is coupled to the positive input of a first operational amplifier a1 and to a first terminal of a resistor r6 the second terminal of the resistor r6 is coupled to ground the capacitor c2 and the resistor r6 operate as a high pass filter for the positive input of the operational amplifier a1 the negative input of the operational amplifier a1 is coupled to ground through the series connection of a resistor r7 and a capacitor c3 the negative input of the operational a1 is also coupled to its output through a resistor r8 the output of the operational amplifier a1 is coupled to the positive input of the second operational amplifier a2 the negative input of the second operational amplifier a2 is coupled to a resistor r9 the other terminal of the resistor r9 is coupled to the sliding terminal of a potentiometer r10 a first fixed terminal of the potentiometer r10 is coupled to ground and the second fixed terminal of the potentiometer is coupled to the negative supply voltage v2 accordingly the appropriate potential can be applied to the negative input of the second operational amplifier a2 through the adjustable voltage divider network of the potentiometer the negative input of the second operational amplifier a2 is also coupled to its output through a.