Accurate Tunable-Gain 1/x Circuit Using Capacitor Charging Scheme

Abstract

This paper proposes an accurate tunable-gain 1/x circuit. The output voltage of the 1/x circuit is generated by using a capacitor charging time that is inversely proportional to the input voltage. The output voltage is independent of the process parameters, because the output voltage depends on the ratios of the capacitors, resistors, and current mirrors. The voltage gain of the 1/x circuit is tuned by a 10-bit digital code. The 1/x circuit was fabricated using a 0.18 mu m CMOS process. Its core area is 0.011 mm(2) (144 mu m x 78 mu m), and it consumes 278 mu W at V-DD = 1.8 V and f(CLK) =1 MHz. Its error is within 1.7% at V-IN = 0.05 V to 1 V.