1. A device, comprising: a current multiplier that multiplies a first current and a current proportional to absolute temperature to generate a second current; an exponential converter that applies an exponential transfer function to the second current to generate an output current, the exponential transfer function depending on a thermal voltage, and temperature dependence of the current proportional to absolute temperature counteracting temperature dependence of the thermal voltage to cause the output current to be proportional to a temperature-independent, exponential function of the first current over an operating range of the device; and a current limiter that imposes at least one of an upper limit and a lower limit on the output current, the current limiter including a first reference-current source directly coupled to an output terminal, an operational amplifier, a second reference-current source coupled to a first input of the operational amplifier, an output and a second input of the operational amplifier being connected via a feedback loop, the output current being applied to the second input of the operational amplifier, and first and second current mirrors coupled between the second input of the operational amplifier and the output terminal, the output terminal outputting a limited current, a reference current generated by the first reference current source setting the lower limit, and a reference current generated by the second reference current source setting the upper limit.