On a new topology for the transconductance feedback amplifier

A new topology for a transconductance feedback amplifier (TFA) is presented in this paper. The topology offers the advantage that it is capable of realizing the negative of the standard inverting gain expression. That is, gains of the form +R₂/R₁. We will also show that it can realize the standard inverting and noninverting gains, all the while maintaining near constant bandwidth in each configuration as gain is varied. This first feature makes the proposed topology attractive for filtering applications since the TFA can function as an integrator, thereby allowing this amplifier to realize positive and negative lossless integrators. The proposed amplifier can also generate the logarithm of an input in the first and fourth quadrants, unlike previous TFA configurations. The proposed amplifier was verified experimentally for different gain configurations, integration and logarithmic capabilities by a chip designed using TSMC´s 0.18-μm CMOS process of a single ended power supply of 1.8 V. The chip occupied an area of 752.6 μm by 581.2 μm and contained the proposed amplifier and a conventional TFA for comparison purposes. A bandwidth of 15 MHz was observed for the proposed TFA in the unity gain (±1) configuration.