This paper presents an analysis on energy dissipation of digital half-band filters operating in the sub-threshold (sub-V_T) region with throughput and supply voltage constraints. A 12-bit filter is implemented along with various unfolded structures, used to form a decimation filter chain. The designs are synthesized in a 65 nm low-leakage CMOS technology with various threshold voltages. A sub-V_T energy model is applied to characterize the designs in the sub-V_T domain. The results show that the low-leakage standard-threshold technology is suitable for the required throughput range between 250 Ksamples/s and 2 Msamples/s, at a supply voltage of 260 mV. The total energy dissipation of the filter is 205 fJ per sample.