A very-high impedance current mirror for bio-medical applications

In many biomedical applications operating at low voltage require very high output impedance current mirror. In this paper, “A Very high impedance current mirror, with less number of transistors which can operate at low voltage without any additional biasing circuitry” is proposed. The proposed current mirror uses MOS current dividers to sample the output current to achieve very high impedance with a large output and voltage range. A feedback action is used to force the input and output currents to be equal. The proposed circuit is also insensitive to the biasing current. This implementation yields an increase in the output impedance by a factor of about g_mr_out compared with that of the super-Wilson current mirror, thus offering a potential solution to mitigate the effect of the low output impedance of deep submicron CMOS transistors used in low voltage current mirrors and current sources. An NMOS version of the proposed current mirror circuit was implemented using an UMC-180nm CMOS process and simulated using Spectre to validate its performance. The output current is mirrored with a transfer error lower than 1% when the input current is increased from 5 to 40 μA.