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Maxim > Design Support > Technical Documents > Application Notes > Audio Circuits > APP 4504
Maxim > Design Support > Technical Documents > Application Notes > Signal Generation Circuits > APP 4504
Keywords: testing, calibration, pure sinewaves, sinewave generators, low THD, phase-locked loops, PLL,
binary frequency dividers, switched-capacitor lowpass filters, external synchronization
APPLICATION NOTE 4504
Locked-Sync Sine Generator Covers Three Decades
with Low Distortion
Aug 17, 2010
Abstract:
This circuit
synchronizes a sinewave output through three decades of frequency (20Hz to 20kHz)
while maintaining low THD and constant amplitude.
A similar version of this article appeared in the September 18, 2009
issue of EDN magazine.
Analog applications such as testing, calibration, and general system
operation often require a sine waveform of accurate amplitude and
frequency, with low total harmonic distortion (THD). Some applications
demand that the generator of such waveforms have the ability to
accurately synchronize the output with an external timing signal. Simple
sinewave generators can offer various degrees of this performance, but
maintaining low THD with constant amplitude is a problem, particularly if
the output and the synchronization signal must remain locked through an extended range of frequencies.
The circuit of Figure 1 can synchronize a sinewave output through three decades of frequency (20Hz to
20kHz) while maintaining low THD and constant amplitude (Table 1). The synchronizer IC (74HC4046) is a
phase-locked loop (PLL) complete with VCO and phase/frequency detector. It has three internal phase
detectors, but the one used here (number 2) has a frequency-capture range equal to that of the VCO
frequency range (f
MAX
- f
MIN
).
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