Low-voltage low-power CMOS rail-to-rail V-I converters

This paper presents three compact and simple CMOS voltage-to-current (V-I) converter schemes attaining rail-to-rail operation with a highly linear V-I relationship over a (-40, +140 °C) temperature range. Based on an OTA/common source amplifier configuration, the key idea to reach rail-to-rail operation is reducing the voltage across the linear resistor that performs the V-I conversion to keep the output current mirroring transistor working in the saturation region over the complete input range. Results for 1.2 V - 0.18 μm CMOS implementations show that all the proposed converters operate over the entirely input range with G_M errors below 2.5%, linearity errors below 0.011% and power consumptions below 70 μW, which makes them suitable for portable applications.