RF power detector for very small changes in signal

Hello,

I am looking for a power detector for measuring shot noise from a tunneling junction. The bandwidth of the shotnoise is between 1Mhz - 5Mhz. When a bias voltage is created between the junction a tunneling current will flow. This current is then converted to voltage by a trans impedance amplifier and subsequently it is possible to amplify this signal by RF amplifiers.

With zero bias voltage (so the current generated by the junction is zero and the signal being measured is due to johnson noise and other noise created by the circuit), the order of the output voltage of this circuit is ~120 microVrms.

I want to be able to measure this signal with a diode detector. I want to then increase the bias voltage from zero volt to some finite volt in some finite steps in such a way that the output voltage will be the following sequence: [120microVrms, 120.1microVrms, 120.2microVrms,... 125microVrms]. This is currently possible by using a spectrum analyzer.

I was wondering if there is a RF power detector that could produce an output that distinguishes the signals in the provided sequence. However looking at the datasheets of the RF diode detectors it is not clear to me what the low level sensitivity(mV/microW?) of the diode/power detectors are.

My question is if the RF power detectors provided by analog have the sensitivity to measure these signals and if so which one is the most optimal to use. Note that we can always amplify our signals from 120microVrms to some higher voltage range.

Any help would be appreciated.

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    •  Analog Employees 
    on Dec 18, 2017 8:51 PM

    I think that you may be better looking at an active detector because they have much better sensitivity. AD8310 (www.analog.com/ad8310), can sense levels down to around -80 dBm which is around 22 uVrms. This is a voltage measuring device. Another option that might be worth a look is a translinear log amp such as AD8304, AD8305 or ADL5304. These devices are  designed to connect directly to photodiodes and convert the log of the photo current into voltage. 

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  • 0
    •  Analog Employees 
    on Dec 18, 2017 8:51 PM

    I think that you may be better looking at an active detector because they have much better sensitivity. AD8310 (www.analog.com/ad8310), can sense levels down to around -80 dBm which is around 22 uVrms. This is a voltage measuring device. Another option that might be worth a look is a translinear log amp such as AD8304, AD8305 or ADL5304. These devices are  designed to connect directly to photodiodes and convert the log of the photo current into voltage. 

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