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measuring amplitude of small high-frequency signal

Everyone,

I need to measure the amplitude of an AC signal of variable frequency between 1 and 15MHz, with amplitudes in the range of a few hundred microvolt (say 100..1000 uV). Available supply voltage is nominally

+-2.7..3.3V or +2.7V/-1.35V (battery powered circuit). The measurement itself does not have to be taken often, a few Hz refresh rate will suffice.

What I'm currently contemplating is to use a high-frequency opamp such as the AD8061 (300 MHz GBW) to provide two stages of gain 20. The stage outputs would be AC-coupled to get rid of the DC offset. This would give me a signal of ca. 40..400 mV which I could rectify and filter. For better linearity I would use an active rectifier circuit, probably using Schottky diodes.

Another alternative I have considered is to use an analog multiplier to square the signal, and then simply lowpassfilter it for the DC component (from which the amplitude is easily calculated). However, I haven't found analog multiplier chips compatible with my battery power supply.

Does anyone of you have a better suggestion?

greetings, Tom

Reply to
Tom
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LTC and Analog Devices, and maybe Maxim, make RF detector chips.

John

Reply to
John Larkin

I read in sci.electronics.design that Tom wrote (in ) about 'measuring amplitude of small high-frequency signal', on Fri, 30 Sep

2005:

In that amplitude range, an ordinary 1N4148 has a square-law response. A Schottky would give more DC output. You can rectify the signal directly (you won't get much DC, but enough) and then amplify the DC. The usual technique is to use two diodes, one in shunt across the signal and one in series with the load resistor, with the signal capacitively coupled to their junction.

Ancient (1950s) RF millivoltmeters, such as the Rohde & Schwartz URV used this technique. But DC amplification is far easier now.

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

15MHz is such a low frequency, why not an active-device peak detector. You could even take some gain.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
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Reply to
Jim Thompson

Why not using a calibrated SW-receiver? Thats the simplest solution. Aperiodic measurement is difficult with tis small values.

rgds Rudy

Tom schrieb:

Reply to
newsrudy

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