Help me realize a divider with AD633

[egs32]

I tried to realize a divider with an AD633, like shown in the data sheet of the AD633, Fig. 7.

The multiplier hisself works well, but I have problems with the divider:

The voltage on X is unproblematic, it is between 0 and + 10V. If the voltage on Y reaches about 3...4 V Volt, on Z (/W) is a sinusoscillation (between -5 and 0 V, 650 kHz). This amplitude increases, if the input voltage aon Y increases. The oscillation stopps, if the input level will be less than 3 V. Changing the OPV does not solve the problem, the oscillation will get another frequency..

The Powersupply is blocked with C=100nF nearby the OPV and Multiplier.

Thank you - Ralf

 

[Ricardo]

how ad633 works

Hi. I was working on a project the other day and I needed to build a circuit that finds the reciprocal of the input voltage. I tried many designs, but had only limited success. Then I noticed that the AD633 could also divide one voltage by another which was perfect. I built the circuit and it worked perfectly - that is until either input voltage was in the region of 5 volts. At these voltages, I got a sinusoidal or triangular oscillation that was greater than about 0.5 MHz. I checked on the internet to see if I could find any help. Well, I didn't find any help, but I did find this post.

After consulting with a lecturer of mine, we found it was very easy to fix the problem. When oscillations occur, the output is DC offset. This indicates that the DC signal is still there, but there is an additional high frequency signal superimposed on the DC signal. So, what we did to fix the problem is to put a capacitor in the feedback path of the op-amp i.e. I placed a 0.47 uF cap between the ouput (pin 6) and the inverting terminal (pin 2) of the op amp. This fixed the problem immediately and killed the bad frequencies. I'm not too sure what you are using this for but you just need to make sure that the frequency and bandwidth that you are using fall well below the frequency of oscillation. My frequency is at most 10 kHz which is much smaller than 500 kHz (or whatever it was - I don't remember ). If you find that you are cancelling out your signal by putting this cap there, you probably need to try a smaller cap - probably 0.22 uF or 0.1 uF, but there is a possibility that the 0.1 uF will still allow oscillations. Also, you could try connecting another cap between the inverting terminal (pin 2) and ground. To work out the size of this cap:
C = 1/(2 * pi * f * R).
R is the equivalent resistance of the parallel combination of the two 10 k resistors, i.e. R = 5 k for the circuit given in figure 7 of the datasheet and f is your frequency.

I hope this helps and that it is not too late. :wink:

 

[enderculha]

divider using ad633

hi!
I am using AD633 as a multiplier. I am multiplying two sinusoids in very low frequency(less than 100Hz). But one of the imput frequency is with offset and İ need to remove it. I used capacitor at the input of the AD633 but the ofset,but i couldn't remove the offset even the offset became negative. I tried with different values of capacitor but it is the same. I couldn't understand the problem, how can i remove the ofset, is there any circuit example?