an 8th order filter is not unusual).Ī digital-to-analogue converter (DAC): You can easily generate a sine wave by feeding it with sine wave digital codes generated in a microcontroller or FPGA. Using a switched-capacitor IC: This is essentially the same method as using cascaded RC filters except by using a switched-capacitor filter IC you can get higher order filters with a smaller number of components (e.g. Using cascaded RC filter is only one way of many to create sine waves! Some other popular methods include: Pretty good! Other Methods Of Making A Sine Wave Remember that the cut-off frequency \(f_c\) for a RC filter is:$$\begin\), we are down to a THD of \(3.8\%\). We’ll design the cut-off frequency of each stage to be equal to the desired sine wave frequency. We’ll configure a timer or PWM peripheral on a microcontroller to output a square wave at \(10kHz\) with a \(50\%\) duty cycle.įor each RC filter, we get to pick either the capacitance or resistance and then calculate the other. Lets say we want a sine wave at \(10kHz\). If this is going to be a problem, active filters can be used (or an amplifier could be added at the end). One disadvantage of the RC filter approach is that the voltage gets attenuated through every stage of the filter. But we can stack many RC filters together until we get a sine wave which is “good enough”. One RC filter does not provide enough attenuation of the higher harmonics. The time domain voltage signal of a 10kHz 3.3V square wave (top) and the FFT of this signal (bottom).
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