1. A device, comprising: a current multiplier that multiplies a first current and a current proportional to absolute temperature to generate a second current; and an exponential converter that applies an exponential transfer function to the second current to generate an output current, wherein: the exponential transfer function depends on a thermal voltage; and temperature dependence of the current proportional to absolute temperature counteracts 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.