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