Maxim > Design Support > Technical Documents > Application Notes > Signal Generation Circuits > APP 1999
Keywords: sine wave, square wave, telecommunication, oscillator, switch capacitor filter
APPLICATION NOTE 1999
Sine Wave Generator Is Crystal Accurate
Jul 25, 1994
Abstract: This application note discusses how to gain greater accuracy and less drift by deriving a sine
wave from a digital source. This results in a stable, frequency-accurate since wave, which is ideal for
servos, test equipment, and telecommunications systems.
Servos, test equipment, and telecommunications systems are among the applications that require stable,
frequency-accurate sine-wave sources. Many such sine-wave oscillators are available, but finding one
with a satisfactory level of absolute accuracy and drift can be a problem.
You can get greater accuracy and less drift by deriving the sine wave from a digital source. Because
square waves comprise a fundamental at the square-wave frequency plus an infinite number of odd
harmonics, you can obtain the desired fundamental sinusoid by removing the harmonics with a lowpass
filter. Switched-capacitor filters suit this application (Figure 1). IC3 is an 8th-order, lowpass Butterworth
type.
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