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Abstract:
This paper describes a small, compact circuit that captures
the adaptation properties of the photoreceptor layer and the
adaptive temporal filtering properties of the laminar layer of the
fly. This circuit uses only six transistors and two capacitors, and
is operated in the subthreshold domain. The circuit has a low DC
gain and a high transient gain. The adaptation time constant of the
circuit can be controlled via an external bias. Its temporal
filtering properties change with the background intensity or
signal-to-noise conditions. The frequency response of the circuit
shows that in the frequency range of 1 to 100 Hz, the circuit
response goes from highpass filtering under high light levels to
lowpass filtering under low light levels (i.e., when the
signal-to-noise ratio is low). A chip with 20x20 pixels has been
fabricated in 1.2µ m n-well technology.
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