isinvariant IsInvariant Sensor Pre-Amplifiers
Aneuran™ IsInvariant™
Sensor PreAmplifiers
(low-power low-cost)
Logarithmic pre-amplifiers are consistent with the Weber-Fechner law:
where perception is constant for features having constant ΔI/I.
Aneuran IsInvariant is a circuit for logarithmic pre-amplification of
  • photodiodes;
  • piezo acoustic crystals; and
  • sensors that fill a medium subject to exponential decay.

    SPICE Trace legend
  • upper trace: 10 decades stepped input;
  • center trace: logarithmic voltage response output;
  • lower trace: simple transient detector.
Note transient height similarity across 10 decades.
The latest IsInvariant pre-amplifier draws no significant current
and has no amplified noise.
Monochromatic cameras with IsInvariant pre-amplified pixels
will have contrast invariant HDR (High Dynamic Range).
Additional IsInvariant technology will enable
logarithmic color invariant HDR (color constancy).
Traces are from a variant on the circuit shown in Patent 7,796,173
and Patent Application (PDF Fig. 13)
SPICE trace from an Aneuran™ IsInvariant™ pre-amplifier