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 1.2V single supply, 1V input output swing and 38 MHz op-amp gain-bandwidth product, 130uW power dissipation with a 10pF load while using 300×300μm2 silicon area. These results are obtained for 0.85V transistor's threshold voltages. Experimental results are shown that verify the correct functionality of both approaches.