This paper presents a ΔΣ modulated digital power amplifier (DPA) with a finite-impulse response (FIR) filter for wireless body area network (WBAN) applications. The proposed DPA utilizes a 1-bit second-order ΔΣ modulator to avoid nonlinearity problem of the multi-level quantization and achieve better quantization noise performance than the first-order modulator. The time-interleaving operation inherently provided by the embedded FIR filter mitigates the mismatching effect of PA cells. The proposed architecture not only improves the out-of-band noise performance but also reduces AM-AM and AM-PM distortions. The proposed ΔΣ DPA is implemented in 65nm CMOS. Simulation results show that it can achieve good out-of-band noise performance with the maximum output power of 6dBm and maximum power-added efficiency of 45%.