4-Bit Parallel-Input Exponential Digital-to-Analog Converter in CMOS 0.18 μm Technology

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 pseudo-exponential 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 mu m 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.