There are many applications that require stability in the operation, such as telecommunications, servos, and test equipment. They are using frequency-accurate sine-wave sources, but to find frequency-accurate sine-wave sources with satisfactory level of absolute accuracy and drift can be a problem, even if there are many such sine-wave oscillators are available.
To get less drift and greater accuracy ws can derive the sine wave from a digital source. We can gain desired fundamental sinusoid by removing the harmonics with a lowpass filter,because square waves consist of a fundamental at the square-wave frequency plus an infinite number of odd harmonics. This application fits using switched-capacitor filters. IC3 is an 8th-order, low-pass Butterworth type.
Switching or sweeping the frequency applied at C1 has a proportional effect on the sine-wave generator output Because the filter’s input and clock frequencies have a fixed ratio of 1:128. Switching or sweeping the frequency
will not affect output amplitude because this band is well below the smoothing filter’s 25kHz corner frequency. The frequencies that represent a potential cause of aliasing in this circuit—the odd-numbered harmonics that exceed half the clock rate—have insignificant amplitudes. So we do not have problem with Alias frequencies.
will not affect output amplitude because this band is well below the smoothing filter’s 25kHz corner frequency. The frequencies that represent a potential cause of aliasing in this circuit—the odd-numbered harmonics that exceed half the clock rate—have insignificant amplitudes. So we do not have problem with Alias frequencies.
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