As usually done in the CMOS microelectronics analog design, amplifiers are implemented by OTAs. For this reason, first of all, in this integrated version, all the OAs employed in [19], [20] and [21] have been replaced with suitably designed low-voltage and low-power OTAs.
In particular, the symmetrical OTA (see Fig. 1) represents one of the most effective topologies proposed in the literature for its good performance (e.g., low input offset) and simplicity. A PMOS differential pair (Q1, Q2) has been chosen in input stage so to further reduce the input amplifier noise; then, a 2 V supply voltage has been set so to make it suitable for portable applications. The designed symmetrical OTA is characterized by a high open loop gain and slew-rate and, in particular, labeling B the current mirror (Q3–Q7) and (Q4–Q8) gains, the OTA open loop gain AO is equal to