Looking for info about Ttrue logaritmic amplifier

[tapa]

True Logaritmic

Hello,

I will like to get any information aqbout true logaritmic amplifier. I mean an amplifier for a IF (for example 60 MHz) that gets on output the function log10(input) (of course at 60 MHz or input IF not a detectec signal).

Can anybody give me a link or information about this kind of circuits.

Than you for all

 

[Debeli]

Re: True Logaritmic

Try www.analog.com, for example AD640.

Regards,
D.

 

[tapa]

Re: True Logaritmic

It's no so easy...

The AD640 is a 120 MHz, 50 dB "Demodulating" Logarithmic Amplifier. I realy need 90 dB and no demodulating.

Y(t)=log10(X(t)) and
X(t)=A(t)*cos(Wo*t+Q(t))
so I need only the log of amplitude, not demodulating the signal... Where I know there is only a manufacturer (and is not on WWW). I will like theory or any posible implementation.

Thank you for all

 

[unkarc]

Re: True Logaritmic

Hi Tapa,

Plessey used to make very good log amps and maybe some of its ICs are still available.
For instance they had the SL531 true log IF amp (10Mhz to 250MHz and log range 70dB) see data sheet at **broken link removed** and see **broken link removed**

[Plessey is merged with Mitel and now is Zarlink]

It is another question where you could buy such IC :?
Here (www.chips2ship.com/s.html) there is a possibility but it is as expensive as gold...

Zarlink has a current product log amp, the SL3522, see **broken link removed** maybe it is more readily available.

regards
unkarc

 

[tapa]

Re: True Logaritmic

More of the same...

This IC is also a log-receiber or detectro. All IC's I found on www are realy a detectro, but the problem is that I don't need a detector only an amplifier. More than a IC I need theory or posible architecture, because I will need to design our own circuit.


Thank you for all