The following figure of the circuit shows a logarithmic amplifier (D1A and the MCP6XXX op-amp) that converts the sensor current (ISEN) to a voltage proportional to the logarithm of the current. R1 maintains negative feedback when ISEN is small and negative. D1B (VCOR) is used to correct D1A for temperature changes.
D1A and D1B are a matched pair in the same package.
If the source (ISEN) is bi-directional, add a diode in parallel with R1 and D1A, and with the opposite polarity to D1A.
Advantages:
Wide dynamic range of current
Good impedance buffering of source
Simplicity
Disadvantages:
Needs temperature correction
Sensor Examples:
Photodiode, e.g., Pulse Width Modulation (PWM) encoded digital signal
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