I my application, i use AD835 to get a*b, which a and b all are DC.
In AD835 datasheet, it say output offset is +-25mV, and input offset voltage is +-20mV ~ +-75mV, how can i cancel this offset?
Or how can i measure this offset.
Apologies for the delay of response. Offset voltage exists inherently due to some non-idealistic property of the amplifier. If you really need to eliminate this offset, I think you can use the Z input pin to calibrate and compensate the offset voltage you are seeing. You can measure and calculate the actual input and output offset voltage of your device by doing some algebra.. You have to use three point system: Given that your circuit is the same with figure 20 of its datasheet. You can do the following.
1. Measure the output voltage for the following inputs:
a. X = 0V, Y = 0V and Z = 0V
b. X = 0.3V, Y = 0.4V and Z = 0V
c. X = 1V, Y - 1V and Z = 0V
2. Substitute the actual values on this equation to get the three equations:
3. Use algebra to get the value of the Vosix (input offset voltage at X input), Vosiy (input offset voltage at Y input) and Voso (output offset voltage)
I hope this helps!
Let me know if you have any other concern.
Thanks for your response.
If i use figure 20 of AD385's datasheet and use three point system. How can i know the U exactly?
Use four point system? Or measure R1 and R2 with a ohm meter?
If R1 and R2 is not present on your circuit, the nominally value of U is 1.05. However, you can adjust the value of U through the use of a resistive divider between pin W (Pin 5) and Z (Pin 4). If you use R1 = 20 x R2, then effective value of U will be equal to 1.
Oh, thanks for your quickly reponse. I will try it.
I can use the Z' input pin to calibrate and compensate the Voso. but how can i cancel AD835 input offset, such as Vosix, Vosiy.
and In my application, i use AD835 to get a*b, which a and b all are AC, which is 60kHz.
This inquiry was answered in 2013. Is this really active again?
p.s. the spec. is over the full temperature range. There is no real specification for the Vosi, however the part is trimmed to zero.
yeah, my input offset voltage (Vosix and Vosiy ) is about 200mV. The circuit is shown in the figure. The SINE is Sinusoidal signal, which is 60kHz without offset. And in the circuit, the V-R is 200mV offset.
So, my question is how can i cancel the input offset. Thanks.
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