Bulk-driven CMOS linear transconductance-cell for AC amplifiers with very low cut-off frequency

This manuscript proposes a novel linearized transconductor for AC amplifiers with a very low cut-off frequency. The cell uses an alternative solution that is based on a modified source-degeneration OTA, using two bulk-driven buffers, incorporating bootstrapping techniques to a buffer and a degenerated resistor. In the buffer, the bootstrapping effect is implemented by using a pseudo-resistor and a linear capacitor properly configured, whereas in the resistor the output voltages of the buffers are used with this goal. Thus, the proposed solution allows realizing a very large time constant, avoiding the use of very large size resistors and capacitors, thus saving chip area. The technique is demonstrated in an 0.18μm CMOS technology by designing an OTA operating with a supply voltage of 0.6 V and achieving a low cut-off frequency of around 2Hz with a power consumption of 462 nW.