Adaptive Circuits Using pFET Floating-Gate Devices

In this paper, we describe our oating-gate pFET device, with its many circuit applications and supporting experimental measurements. We developed these devices in standard double-poly CMOS technologies by utilizing many eeects inherent in these processes. We add oating-gate charge by electron tunneling, and we remove oating-gate charge by hot-electron injection. With this oating-gate technology, we can not only build analog EEPROMs, we can also implement adaptation and learning when we consider oating-gate devices to be circuit elements with important time-domain dynamics. We start by discussing non-adaptive properties of oating-gate devices and we present two representative non-adaptive applications. First, we discuss using the oating-gate pFETs as non-volatile voltage sources or potentiometers (e-pots). Second, we will discuss using oating-gate pFETs to build translinear circuits that compute the product of powers of the input currents. We then discuss the physics, behavior, and applications of adaptation using oating-gate pFETs. The physics of adaptation start with oating-gate pFETs with continuous tunneling and injection currents. A single oating-gate MOS device operating with continuous-time tunneling and injection currents can exhibit either stabilizing or destabilizing behaviors. One particular application is an autozeroing oating-gate ampliier (AFGA) that uses tunneling and pFET hot-electron injection to adaptively set its DC operating point. Continuous-time circuits comprising multiple oating-gate MOS devices show various competitive and cooperative behaviors between devices. These oating-gate circuits can be used to build silicon systems that adapt and learn. In 1967, Kahng and Sze reported the rst oating-gate structure as a mechanism for nonvolatile information storage 1]. Since then, oating-gate transistors have been used widely to store digital information for long periods in structures such as EPROMs, EEPROMs, and ash memories. These digital nonvolatile memory technologies have only been fabricated on specialized and expensive processes. FGMOS transistors have also been used as long-term non-volatile information storage devices for analog applications 2]. The focus of this paper is show that oating-gate devices are not just for memories anymore, but are also computational circuit elements with analog memory and important time-domain dynamics. We will paint a coherent picture of the capabilities of pFET oating-gate devices starting from the work that we 3-15] and other colleagues 16-22] have developed over the last 10 years, and including recent research results. We emphasize pFET oating-gate devices in this paper because any CMOS process will always have pFET injection for subthreshold and above-threshold biases. A second and related focus is to show the availability and …