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ADL5902 vs. AD8312 vs. AD8362 or which?


I am new to RF, so excuse please.

My CDMA 3G phone has a reading in its settings that says it puts out -77 dBm or thereabouts when making or receiving a call.

While idle, it says -82 dBm.

I read similar dBm on another CDMA phone.

These phones operate either in the 800MHz or 1.9Ghz band according to the carrier's dox.

I want to design with an RF detector chip that will detect when this phone is in use and provide a signal strength output. The same chip needs to be able to detect and provide a signal strength output for the Wi-Max band (3.5 GHz).

In one of AD's tutorials I read that the best choice for CDMA and Wi-Max is an RMS detector rather than logarithmic. True?

For lower frequencies I have been using an inductor as the antenna, but have since read that an inductor will not work with GHz digital outputs.


What kind of antenna is best to use?

What is the circuitry that connects this antenna?

Can I use one antenna for multiple frequencies?

Is there some documentation to read about this that goes along with the RF chips?

For a chip such as AD8362 which the output is "linear in dB", what does this mean, and do I need another chip to decode?

  -Getting a linear voltage output is most desirable simply because it seems the easiest to work with.

Thanks in advance.

  • Antenna Recommendation:

    Making an antenna recommendation is a bit beyond the scope of my knowledge. It will need to be as broadband as possible to cover the frequency range in which you want to operate. I would recommend that you start your search on the Richardson website (

    Connecting to Antenna:

    RF detectors are typical sensitive down to around -60 dBm. So if you want to detect signals at lower levels, you will need a low noise amplifier. I would recommend ADL5602 in this case becasue it is broadband and has a reasonably good noise figure.


    Linear-in-dB means that the transfer function of the detector has a slope with the unit V/dB. For example 50 mV/dB is a typical slope for an rf detector. So if the input signal changes from -60 dBm to -50 dBm     or  from -10dBm to 0 dBm, the delta at the output of the detector will be the same.

    RMS vs. Non-RMS

    If the signal type that you are going to be measuring will be changing (e.g. in terms of its peak-to-average ratio), then an rms responding detector is better because it is immune to changes in peak-to-average ratio. I would recommend ADL5902 (broadband operation with high dynamic range).

    Further reading is in the attached ap notes and articles. Also, see CN0178 and  CN0150 Circuits from the Lab

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