A 120dB input dynamic range, current-input current-output CMOS logarithmic amplifier with 230ppm/°K temperature sensitivity

This paper presents the design of a current-mode CMOS logarithmic amplifier, which by design is insensitive to ambient temperature variations. Its operational current ranges over 100fA-100nA, which covers the full range of sub-threshold region. Unlike conventional logarithmic amplifiers, the proposed approach directly produces a current signal as a logarithmic function of the input current. The core of the proposed circuit is translinear ohm's law principle, which is implemented by a floating-voltage source and a pseudo-linear resistive element within a translinear loop. The temperature sensitive parameters are reduced using a translinear-based resistive cancelation technique. Measured results from prototypes fabricated in a 0.5 μm CMOS process show that the amplifier exhibits an input dynamic range of 120dB and a temperature sensitivity of 230 ppm/°K.