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In this paper, a new digitally controlled linear-in-dB CMOS variable gain amplifier is proposed. The circuit employs the proposed novel approach in achieving a wide-range true-exponential transfer function e 2X using a traditional pseudoexponential amplifier followed by a variable gain stage, to expand the output dynamic range. A single digitally controlled variable resistor is used to tune the circuit accordingly by controlling X with a digital word. The result is a digitally controlled data conversion that yields a new type of non-linear digital-to-analog converter. Finally, a 4-bit converter is implemented in a TSMC 0.18 µm CMOS technology and displays a gain from about −21 dB to 36 dB in steps of 3.89 dB with an output linear error in [−0.66, 0.45] dB and a static power consumption of 2.34 mW.

This brief presents an 84-dB dynamic range true logarithmic amplifier. Logarithmic ordering in the output is achieved as a function of control parameter X , which in turn is tuned digitally. The result is a digitally controlled data conversion that yields a new type of logarithmic digital-to-analog converter. This 4-bit nonlinear converter has been fabricated in a TSMC 0.18-μm complimentary metal-oxide-semiconductor technology. Measurement results confirm theory and simulations, and display logarithmic transfer characteristics within [−1.36%, 0.84%] output linear error. The integrated circuit has dimensions of 1.5 × 1 mm 2 and an average power consumption of 13.2 mW when powered with ±1.65-V supply voltages.Index Terms-Digitally controlled variable resistor, dynamic range (DR) expansion, logarithmic digital-to-analog converter (DAC), pseudologarithmic amplifier, variable gain amplifier.

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