Hello,

I am testing my new ADL5391-Evaluationboard, and coming across with the following problem. As you can see on the figures, the multiplication output is somehow disturbed. The output is not a proper sine-function anymore. Some peaks are higher, some smaller.  It seems that the two input sin/cos-functions internally get some DC before multiplication. I use the board in single-ended mode, so I added an 56Ohm resistor for R2. Any ideas how to fix this problem?

Thanks!

Best regards,

Sam

Squaring result of sine-function

Squaring result of rect-function

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• Hi Sam,

I'm wondering if what you are seeing is the fundamental bleedthrough deconstructively interfering with the 2nd harmonic (see page 11 in the datasheet for the case of squaring a sine wave).  Unfortunately, due to the part having internal DC offsets, this provides a mechanism for the fundamental to bleedthrough to the output.

I have not gone through the trigonometric math for the "sine * cosine" case, but I have a feeling the interference could be worse.

You could try a couple of things:

1)  Bandpass filter the output at the frequency of interest (the second harmonic)

2)  Put a DC offset on the inputs to null out the internal DC offsets that are causing the bleedthrough

If indeed the problem is due to the bleedthough, the output filter might be the easiest experiment to confirm this.

Hope this helps,

Joel

• Hi Sam,

I'm wondering if what you are seeing is the fundamental bleedthrough deconstructively interfering with the 2nd harmonic (see page 11 in the datasheet for the case of squaring a sine wave).  Unfortunately, due to the part having internal DC offsets, this provides a mechanism for the fundamental to bleedthrough to the output.

I have not gone through the trigonometric math for the "sine * cosine" case, but I have a feeling the interference could be worse.

You could try a couple of things:

1)  Bandpass filter the output at the frequency of interest (the second harmonic)

2)  Put a DC offset on the inputs to null out the internal DC offsets that are causing the bleedthrough

If indeed the problem is due to the bleedthough, the output filter might be the easiest experiment to confirm this.

Hope this helps,

Joel

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