Low voltage CMOS op-amps for a supply close to a transistor´s threshold voltage

Two schemes for low-voltage CMOS op-amp operation with large input signal swing and constant gm are presented. One of the schemes is based on the use of capacitive dividers with multiple-input floating-gate transistors and the second on a novel concept denoted dynamic battery biasing that uses a battery to keep the op-amp input terminals close to one of the supply rails. Simulations are presented that verify the schemes operating with a 1.2 V single supply, 1 V input output swing and 38 MHz op-amp gain-bandwidth product, 130 μW power dissipation with a 10 pF load while using 300×300 μm² silicon area. These results are obtained for 0.85 V transistor´s threshold voltages. Experimental results are shown that verify the correct functionality of both approaches