Frequency-dependent harmonic-distortion analysis of a linearized cross-coupled CMOS OTA and its application to OTA-C filters

Abstract

Recent progress of wide-band communication systems demands high-frequency circuits. Conventionally, the linearity of the operational transconductance amplifier and capacitor (OTA-C) has been analyzed using Taylor series expansion. Unfortunately, this approach does not predict the frequency-dependent linearity degradation. Thus, to properly design linearized OTAs, the frequency dependence of these coefficients must be determined. In this paper, we present a frequency-dependent harmonic-distortion analytical method applied to a linear-enhanced OTA. This OTA, which is suitable for high-frequency operation, uses three linearization techniques simultaneously: 1) attenuation through floating-gate MOS transistors; 2) source degeneration; and 3) polynomial cancellation techniques. By using the harmonic-distortion analysis, some properties on the performance of OTA are used to improve the performance of OTA-C based circuits at high frequencies. A 0.5-/spl mu/m CMOS OTA simulation and experimental results are shown to verify the harmonic-distortion analytical method.