A Low-Power, Compact, Adaptive Logarithmic Transimpedance Amplifier Operating over Seven Decades of Current

This paper describes a transimpedance amplifier using logarithmic compression of the input current for wide dynamic range current sensing applications. Measurements demonstrate operation over currents ranging from 200fA to 2muA with an average error of 0.8%. It is analytically shown that the power dissipation of the non-adaptive structure varies linearly with dynamic range. This amplifier alleviates this strong dependance on dynamic range and achieves low-power operation by adapting the bias current of the amplifier depending on input current thus burning an average power of 3.45muW per decade of current. Either SNR or bandwidth can be made to trade-off with the input current depending on application. If the bandwidth is limited to 5kHz, it achieves an average SNR of 65dB.