from Section II - Low-power analog and biomedical circuits
Published online by Cambridge University Press: 02 December 2010
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Barrie GilbertIn this chapter, we shall discuss circuits that use current inputs and current outputs to create static and dynamic linear and nonlinear systems. Current-mode circuits can operate at low power-supply voltages and over a wide range of currents with exponential subthreshold or bipolar transistors. For reasons that will become clear at the end of the chapter, current-mode signal processing implemented with exponential devices is also often termed log-domain signal processing.
We shall begin by discussing static translinear circuits, which were invented by Barrie Gilbert in the bipolar-circuit domain and that are easily generalized to the subthreshold-MOS domain. Then, we shall discuss circuits for constructing linear current-mode dynamical systems analogous to Gm − C filters in the voltage domain, which were invented and developed by Seevinck, Tsividis, Frey, Toumazou, Andreou, Vittoz, Minch and others. We shall present gain-control techniques for achieving a nearly constant signal-to-noise ratio over a wide dynamic range of inputs, developed by Tsividis for use in linear current-mode input-output systems. Such adaptive techniques separate signal-to-noise ratio (SNR) and dynamic-range variables enabling low-power operation over a wide dynamic range of inputs.
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