Amplifier oscillation while cascading other ICs

Hi all,

I would like to design a single multiplication circuit with a multiplier IC, AD835.
The input of the AD835 is a 6M signal from an amplifier, MAX4451, and a 1M signal from an Ardunio broad.
The problem is: when I check the 6M signal from the amplifier without connecting the multiplier, its shape is good.
But, while connecting the 6M and 1M signal as the inputs of the multiplier, both 6M and 1M signals have lots of noise.
I wonder if the amplifier starts to oscillate while connected to other ICs, and how to eliminate it?

Thanks a lot.

Start with whether the "noise" has any particular
frequency content - particularly content that makes
sense like 5MHz, 7MHz (6 +/-1) and also if the signals
are square rather than pure sine, mix-products of their
harmonics as well.

Depending on mixer / multiplier style, there could be
kick-back noise (especially if the mixer is meant for
50-ohm systems and you drive it with something wimpy).

On the other hand requiring too much drive from an
amplifier could contaminate ground or supply and feed
into the signal chain at various places. If the "noise"
can't be shown to have well defined frequencies then
maybe a loop of this sort is in play.

You do not mention what happens when the 6M or the
1M is connected to the multiplier, alone. This could yield
clues.

dick_freebird said:

You do not mention what happens when the 6M or the
1M is connected to the multiplier, alone. This could yield
clues.

Click to expand...

Thanks for you respond. As you can see,
the 6M signal from the amplifier without connecting the multiplier, its shape is good(pink one).


while connecting the 6M and 1M signal as the inputs of the multiplier, both 6M(pink) and 1M(yellow) signals have lots of noise.


Don't know how the amplifier output is effected.
Thanks.

Hi,

Can you show your circuit? Schematic and PCB layout.

Are these logic sinals? Maybe you could use an AND gate, or an analog switch instead of an anlog multiplier.

Klaus

Hi Klaus,

Yes, an analog switch maybe can do this, but I haven't found a proper one to cover +-3V, 6M signal. I'll give it a try.
Thanks!