About DLVA (Detector logarithmic video amplifier) ?

[Dillon]

I design a DLVA in 2-18GHz,Dynamic Range >40dB, how to choose the detector diode and the logarithmic video amplifier?who has the relative paper or advise , please send to me .

Thanks a lot.

 

[Dillon]

Is there anybody can help me ?
Thanks.

 

[G4BCH]

These are not easy things to design.
There was a book published by Artech house called Logarithmic Detection or something similar. I don't know if it is still in print and I don't have a copy, I just read a very small part of it many years ago- not the DLVA part.
If I remember correctly you need a tunnel diode for the detector or a zero biased schottkey. The video amplifier was I tink just a log converter function., similar to an opamp with a diode in the feedback.

Not much to go on, but a start I hope.

 

[Dillon]

If I use HM1301 for tunnel diode and AD8310 for video amplifier, is it can be achieved?
which is better by DC couple or by AC couple?how to design it?

Thanks!

 

[G4BCH]

Assuming the diode you have chosen will work over your frequency range it should be OK, and the AD8310 will do the log conversion .
As to AC or DC coupling, if you need to detect cw signals then it has to be DC.
You will have to take great care coupling into the log chip with DC unless you can float the diode above ground. The offset current at the input of the chip may present a drift problem unless it is very low.

Good Luck

 

[Dillon]

Did anybody have any solution to solve the problem, the offset current impact the diode greatly.Does it can be insulated?how to do it? Please give me some advice.

Please help me ,Thanks.