An autozeroing floating-gate amplifier with gain adaptation

Paul Hasler and Paul D. Smith Georgia Institute of Technology Atlanta, GA 30332-0250 [email protected] ABSTRACT Recently, we have characterized and modeled oating-gate circuits that adapt their oating-gate charge based upon statistics of the incoming signal. In this paper, we show signal-dependant adaptation in three oating-gate circuits. First, we show classic autozeroing oating-gate amplifer (AFGA) measurements of output voltage adaptation, as well as AFGA measurements of o set adaptation for large output amplitudes. Second, we measure and characterize current adaptation of a transcondutance element, where the current increases for increasing signal level. Third, we measure and characterize the amplitude and o set adaptation in a oating-gate circuit built from the rst two circuits; amplitude adaptation only occurs over a nite range of input parameters and timescales. Floating-gate circuits using continuous tunneling and injection naturally adapt the oating-gate charge in response to various applied input signals. Our previous investiagations have shown basic adapting circuits, like the autozeroing oating-gate ampli er (AFGA), that adapt away a single feature of an incoming signal [1]. Recently, we have characterized and modeled oating-gate circuits that adapt their oating-gate charge based upon statistics of the incoming signal [2]. This result is the rst indication that oating-gate devices with continuous tunneling and hotelectron injection currents are capable of large-scale adaptation. This paper continues this work by showing signalbased adaptation in three oating-gate circuits. In the third circuit, we show amplitude adaptation over a nite range of input parameters and timescales. 1. ADAPTIVE FLOATING-GATE CIRCUITS In this section, we will consider the behavior of the two continuously adapting oating-gate circuits shown in Fig. 1. These two circuits are the two key pieces making up the AFGA with gain adaptation. In the interest of clarity, our experiments and modeling will only focus on the lowfrequency and passband responses, ignoring the high-frequency dynamics. 1.1. Autozeroing Floating-Gate Ampli er We begin our examination of adaptive oating-gate pFET circuits by examining the autozeroing oating-gate ampli er (AFGA) which appears in Fig. 1a. The AFGA Vt Vout Vdd C1 Vin Vtun1 Vfg