Simulation of Harmonics in an Operational Amplifier to Determine the Signal-to-Noise-Ratio

Abstract

- In this work, the output of a simplified model of an operational amplifier (OA) with noise coupled to the input signal exhibits nonlinearity. Attenuation at the input can reduce harmonic distortion (HD) by some mathematical relation to correct the distorting effect at the output of the amplifier. Assuming an audio speaker produces less than 9 percent distortion at 1 kHz with a 1volt input, this is measured with respect to the fundamental (THD-F). Viewing the effect of the amplifier's nonlinearity, a periodogram of its output when stimulated with a sinusoid set to the maximum allowable voltage of the amplifier 2 Vpk for a duration of 50ms. The methodology includes characterizing a nonlinear OA with memory and an adaptive Digital Pre-Distortion (DPD) feedback system to reduce the output signal distortion level. The initial step in the procedure is to determine the coefficient matrix needed for selecting the Volterra memory polynomial model. This step uses actual measured data for the OA. After deriving the set of coefficients for the OA model, a system-level simulation is performed. This system includes an adaptive DPD algorithm that can be enabled during simulation using the toggle switch and demonstrates how the linearity of the output signal improves DPD correction. Two signals are created a fundamental frequency of 𝜋 4 rad/sample with amplitude 1 and the first harmonic of frequency 𝜋 2 rad/sample with amplitude 0.025. One of the signals additionally has additive white Gaussian noise with variance 0.05 2 , setting the random number generator to the default sceneries for reproducible results; the SINAD for the signal without additive noise and comparing the result to the theoretical can be outputted.