Multiplier AD835 Noise Elimination

Hello,

I don't really know of any warnings at about the part. Are you reporting the source signals develop noise? If so, what are the wave-shapes of the signals, i.e., sinusoids, square, etc.? Also I assume the source is some other board, or maybe two boards? If so, are the lines terminated to minimize reflections? When the AD735 or any other multiplier is used the power pins need to be carefully by-passed. Think parallel large and small values such as 4.7uF in parallel with a 10nF, etc.

1MHz and 6MHz are high enough frequencies to take care with. You might benefit from input buffers ahead of the AD735. I've not encountered  such a circuit application before.

Good luck,

js

Hi Js,

Yes, the input waves are square waves from different broads like the yellow and pink lines below.

The blue line is the output of the multiplication(yellow * pink). As you can see, some noise appeared,

so the blue wave is not flat and even can't be recognized. 

In that event I suspect you might have some oscillation due to the mode of transferring the signal between boards. This would be typical of an unterminated coax, or perhaps no coax at all. The fix is to add a resistor to the drive end of the connection between boards. I know of no reason why the multiplier would cause noise as shown, but capacitance or lack of termination could. The ideal situation is 50 ohm or 75 ohm on both sides of the connection but a lossless way is just 50 - 100ohms in series with the line.

 Best,

js