measuring AC rms voltage of TMP36 using TDS Tektronix 2002C digital oscilloscope
Consider temperature as a DC voltage that ramps slowly.


add a low pass RC filter such as 100k to 1uF near ADC input, so the fastest change full scale possible is  1V/100ms or 1mV/100us
consider averaging 100 readings to reduce noise / sq.rt.(100)= 1/10th noise.  There is no signal frequency from sensor, only DC at fixed temp.
you are oversampling temperature at 1000x rate necessary. you could accumulate N results and divide by N to reduce jitter by \$\ N^{\frac{1}{2}}\$ and/or add RC 


This should give you much better results for TMP36 with 10mV per 'C with 0.5V offset at 0'C