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AD650

Question asked by kdyga on Jul 24, 2015
Latest reply on Jul 28, 2015 by kdyga

Hello,

 

I'm trying to use AD650 as a frequency to voltage converter.

Requirements:

Fin max = 1MHz, Voltage =0-10V.

From the calculator on the website I obtained Rin=11,11KOhm, Cint= 1.44e-5, Cos=8.824e-11. So I applied Rin=11,5kOhm, Cint=82pF, Cos=15uF.

 

The problem is, that during measurements, the output voltage changes in weird way, by what I mean:

1MHz      9.4V

900kHz    8.4V

800kHz    7.4V

700kHz    6.5V

600kHz    5.6V   

500kHz     9.5V

400kHz     7.5V

300kHz     5.6V

200kHz     5.6V

100kHz     5.6V

90kHz     5.89V

80kHz     5.21V

70kHz     4.5V

60kHz     3.9V

50kHz     3.2V

40kHz     2.72V

30kHz     2.06V

20kHz     1.4V

10kHz     0.6V

9kHz     0.593V

8kHz     0.527V

7kHz     0.458V

6kHz     0.393V

5kHz     0.331V

4kHz     0.268V

3kHz     0.205V

2kHz     0.138V

1kHz     0.070V

900Hz     0.063V

800Hz     0.060V

700Hz     0.053V

600Hz     0.045V

500Hz     0.040V

400Hz     0.030V

300Hz     0.023V


Does anybody have an idea what's going on? And why the results are so weird? Is this satndard behaviour? Hope not...

Especially,

1. Why there is a voltage jump up to the max voltage output reserved for max frequency?

2. Why the voltage is stable between 300kHz and 100kHz?

3. Why the voltage rises in 90kHz, when it should decrease?


I really need somebody's help


Kate

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