??? 11/09/05 11:49 Read: times |
#103466 - Analog out from PWM |
Sir;
In one of my projects I am using pwm from ADUC845 to get an analog output, the PWM out put from ADUC845 is at a frequency of 200Hz. This 5V pwm is given to a not gate Ic (74HC14) and its output is given an RC of Value 3.3M and 3900pF. Then to a Sallen Key filter with Pole - 2 Cuttof frequency - 10Hz Pass Band - Low Pass The output of the filter ranges from 1 to 4V. The linearity, Accuracy, Stability all found to be OK till mV level. But when Tempco test (30 – 50 degree C) was performed it shows a shift of 12mV at the filter output, which is not allowed. I am using NPO capacitors with +/- 2% tolerance. Op-amp used is TLE272. What can be done to improve the performance? Increasing Frequency could have helped but I cannot increase the pwm Frequency due to the constrains in the controller. (Dual channel used) Please take this into consideration and give your valuable suggestions and ideas to improve the Tempco. Regards Jayan |
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