AN1712 datasheet(6/14 Pages) STMICROELECTRONICS

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GENERATING A HIGH RESOLUTION SINEWAVE USING ST7 PWMART

2 IMPROVING SINEWAVE RESOLUTION

Sinewave resolution depends on three factors:

– tPWM

– the number of samples in a sinewave cycle

– “COUNTER” value

By changing any of these parameters you can get a different resolution.

If fCOUNTER is fixed, you can only change tPWM by varying the ARTARR value. The minimum

change you can do to ARTARR is 1. So, the minimum change in tPWM is tCOUNTER. For ex-

ample:

If fCOUNTER is 4 MHz and ARTARR value is 56, then tPWM is 50us. If the number of samples

in a sinewave cycle is 40 and COUNTER is 10, fSINE will be 50 Hz.

If you change the ARTARR value to 57, tPWM will change to 49.75us. So, fSINE will be ~50.25

Hz (assuming the number of samples and COUNTER value are fixed). So, the resolution is

~0.25 Hz.

Now to improve resolution, change ARTARR = 36, COUNTER = 7 and number of samples in

a sinewave cycle = 52.

Assuming fCOUNTER is still 4MHz, tPWM will be 55us. In this case fSINE will be 49.95 Hz, which

gives improved resolution (~0.05Hz).

AN1712 Datasheet(PDF) 6 Page - STMicroelectronics