High_purity_sine_wave_generator

Published:2009/7/24 7:46:00 Author:Jessie | From:SeekIC

By combining a MAX270 4th-order low-pass filter, a 74HC163 counter, and an 8-channel analog MUX, high-purity 1- to 25-kHz sine waves are generated with a THD of less than -80 dB. The low-pass filter is set to the desired frequency and a clock 8 times the sine frequency is applied to the 74HC163 counter. The MAX270 uncommitted op amp sets the filter output level. Gain accuracy is set by the MAC270 gain at the corner frequency, which is guaranteed between -2.4 and -3.6 dB at 1 kHz. The 100-kΩ potentiometer provides gain control if desired. Two resistor dividers provide the input voltages that are required at the MUX inputs. When the MUX switches through channels 0 to 7, an 8-times oversampled staircase approximation of a sine wave is generated. Compared with a square wave, the oversampled waveform greatly reduces smoothing-filter requirements by pushing the first significant harmonic out to 7 times the fundamental. All higher-order harmonics are filtered to below -80 dB by the MAX270. Maxim , 1992, Applications and Product Highlights, p. 7-7.



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