zhivko me

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11 years ago.

PWM out noise

Hi,

I am using P21 for 3.3V pwmout, with period 100us, duty 50us. Since I am feeding this signal to opamp (opa211) that controls current source, I need to reduce voltage of mbed 3.3V signal to 0.100V (100mV).

To lower voltage I am using voltage divider with 32k and 1k as seen in picture. The voltage after 32k resisotr is already pretty noisy (check picture). How can I reduce that noise?

Thanks for any suggestion

/media/uploads/zhivko/mbed_pwm_out.png /media/uploads/zhivko/osciloscope.jpg

2 Answers

zhivko me
poster
11 years ago.

OK, I used short gnd probe on osciloscope to measure this. I found out that if I move gnd of power supply closer to osciloscope probe gnd, the noise reduce significantly... Is there even a chance to work with so small voltages (100mV) on breadboard - and make quality measurements? Are there more quality breadboards that solve this noise problem?

For sure always place your probe ground connection as close as possible to where you are measuring your signal. So in this case probably just the ground of the mbed.

posted by Erik - 11 Feb 2014
Ravneet S
11 years ago.

.