Reconfigurable and Dense Analog Circuit Design Using Two Terminal Resistive Memory

Metal-oxide based bipolar Resistive RAM (RRAM) is one of the most promising candidates for the future non-volatile data storage. Due to unique properties e.g., small footprint, ability to modulate resistance states in wide ranges dynamically, hysteresis and CMOS compatibility, RRAM can be a fruitful candidate for analog circuit design. However, the recent literature only scratches the surface of this interesting prospect. In this paper, a single RRAM behavior is studied under temperature, voltage and process variations from an analog design standpoint. A comparative study is performed between two analog circuits namely, Common Source (CS) amplifier and differential amplifier with traditional passive resistors and with passive resistors replaced by RRAM along with two other design examples, namely constant $g_m$gm biasing circuit and active low-pass filter, where RRAM can be integrated into analog circuits. Our study shows that blind swapping of passive resistors with RRAM in analog circuits can actually degrade the performance metrics. We propose techniques such as usage of RRAM Low Resistance State (LRS) to recover the loss. We also note that hyperbolic I-V characteristics of RRAM can inherently improve the linearity of RRAM based analog designs. Simulation results indicate that RRAM based amplifiers can achieve 2X area reduction, about 1.5X higher bandwidth with only $\approx 9\%$approximate to 9% reduction in gain. The resistance modulation property of RRAM is applied to realize a source degenerated amplifier with reconfigurable linearity, to a constant transconductance bias circuit to avoid resistance trimming and to design a programmable active low pass filter.