A Low Power OTA-C Filter for Wireless Body Area Networks

The traditional OTA structure uses the current splitting technology to decompose most of the current, which can effectively reduce the transconductance, but the excessive current splitting ratio will bring power loss. To solve this problem, a multiple-output fully differential (MOFD) cascode OTA structure is proposed. This structure can generate additional output by connecting the load to the current splitting branch, which can effectively utilize the current generated by the current splitting to reduce the power loss. In order to reduce the passband attenuation of the filter, the output stage adopts the cascode structure to increase the output impedance of the OTA, and the improved source negative feedback structure obtains lower transconductance and better linear range. Compared with the traditional structure, the number of OTAs of the fifth-order Butterworth low-pass filter with this OTA structure is reduced from 11 to 6, thereby reducing power consumption and achieving lower passband attenuation. The circuit is verified by 0.18 um CMOS process. The results show that the passband gain of the proposed filter is only −6.1 dB. −3dB frequency is 260 Hz. For 100 mV sinusoidal input signal at 50 Hz, the total harmonic distortion (THD) of the filter is about −66 dB and the power consumption is only 11.4 $\mu \mathbf{W}$ at 1.8 V supply.