A low-power bioamplifier with a new active DC rejection scheme

We present a bioamplifier suitable for massive integration in implantable recording medical devices. This amplifier achieves reduced size and lower power consumption, compared to previous designs, by means of a novel DC rejection scheme. DC rejection is achieved by an active integrator located in the feedback loop of the bioamplifier. It places a highpass cutoff frequency within the transfer function, which is set by a small capacitor and a MOS-Bipolar equivalent resistor. This configuration rejects large DC offset and drift that exist at the electrode-electrolyte interface without the need for input RC networks or area consuming capacitors feedback networks, thus preserving the bioamplifier´s high input impedance and small size. The proposed bioamplifier, designed in a 0.18-mum CMOS process, provides a midband gain of 53 dB, passes the neural signal from 105 Hz to 9.2 kHz and achieves an input-referred noise of 5 muVrms. It occupies less than 0.064 mm² and dissipates 8.4muW