FAQ: Operating the AD8364 dual RMS Detector at frequencies below 450 MHz

Document created by enash Employee on Nov 15, 2010Last modified by AndyR on Jan 31, 2012
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Q.

The AD8364 datasheet provides specification data down to 450 MHz but says that operation down to "Low Frequencies" is possible. Do you have any advice on operating this device below 450 MHz.

 

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A.

Normally, we recommend driving the RF inputs differentially using a balun. Providing a balanced signal to the RF input tends to maximize dynamic range, particularly at the top end. However, at lower frequencies (e.g. lower than around 450 MHz), this becomes less critical and you can consider driving the device with a single ended signal (the unused input is then ac-coupled to ground).  This is described in more detail on page 36 of the Rev 0 data sheet. Of course, you can still drive the device differentially using a balun. In choosing a balun/transformer, you should look for good amplitude and phase balance (i.e. outputs are 180 degs out of phase) at the frequency of interest.

 

When operating at relatively low frequencies, you also need to be conscious of an internal offset nulling loop. If your input frequency is low enough, this loop will mistake it for an offset voltage and will try to servo it away. Fortunately, you can get around this by adjusting the size of the CHP capacitor (pins 1 and 24). This is also described on page 36 of the rev 0 data sheet. 

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