MSP430FG6626 CTSD16 INPUT

Krishn_JI

Other Parts Discussed in Thread: MSP430FG6626

HELLO

i am working on msp430fg6626 controller and want to sample sine wave signal using CTSD16 adc. In application note SLAS874 page no.51 analog signal input range is mentioned, But i am not getting that point properly so please explain it. i am using internal reference generator with 2.5v and offset binary data output format with more than 32768 samples are 2's complimented . one of the plot of output samples i have was as attached below.

one another problem is when i apply continuous sine wave i am getting space between two cycles which is not desired please see below images.

over 9 years ago

0 Clemens Ladisch over 9 years ago

Guru 322640 points

You are not using the correct data format.

And one half of the wave goes below the lower reference voltage.

0 Krishn_JI over 9 years ago in reply to Clemens Ladisch

Expert 2145 points

i am using offset binary data formate and applying pure sine wave signal. i want to know that what is analog signal input range for single ended input on A0 channel(p6.0) of CTSD16. i have selected 2.5v internal reference. when i measure on Vref pin of mcu i am getting only 1.15v

0 Clemens Ladisch over 9 years ago in reply to Krishn_JI

Guru 322640 points

And ADC has two reference voltages, for both ends of its input range.

You did not tell us about the lower reference voltage, so it's probably ground. And your input signal apparently goes below ground.

0 Krishn_JI over 9 years ago in reply to Clemens Ladisch

Expert 2145 points

Hii
i don't know how to apply negative reference voltage please explain in detail. i want to set negative reference also at -2.5v so that i can apply +/-2.5v single ended sine wave single for sampling

0 Clemens Ladisch over 9 years ago in reply to Krishn_JI

Guru 322640 points

Neither the reference voltages nor the input signals can be below ground (see table 5-35 in the datasheet).

You have to apply an offset to the input signal to move it into the valid range.

0 Krishn_JI over 9 years ago in reply to Clemens Ladisch

Expert 2145 points

That means i have to up the DC level of my signal so that the complete level comes upward from ground level...

0 EyeballMSP over 9 years ago in reply to Krishn_JI

Prodigy 80 points

It looks like the signal is getting chopped due to the reasons mentioned above. It's clear the top of the sine wave has been displaced to the negative side of the graph - like reversed polarity.

Maybe worth a look at the code?

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MSP430FG6626 CTSD16 INPUT