Silicon neuron circuits emulate the electrophysiological behavior of real neurons. Many circuits can be integrated on a single very large scale integration (VLSI) device, and form large networks of spiking neurons. Connectivity among neurons can be achieved by using time multiplexing and fast asynchronous digital circuits. As the basic characteristics of the silicon neurons are determined at design time, and cannot be changed after the chip is fabricated, it is crucial to implement a circuit which represents an accurate model of real neurons, but at the same time is compact, low-power and compatible with asynchronous logic. Here we present a current-mode conductance-based neuron circuit, with spike-frequency adaptation, refractory period, and bio-physically realistic dynamics which is compact, low-power and compatible with fast asynchronous digital circuits.