FM LNA with output voltage regulated
FM LNA with output voltage regulated
(OP)
Hi all!
I have to design a FM LNA with output voltage regulation.
The specs are:
output voltage of amplifier between 90 to 105dBuV for an input level from (90-amplifier gain) to 120dBuV.
Does anybody know how can I design this control?
At the moment I have a FM non regulated amplifier. Is there any way to add the regulation to this design?
Thanks a lot!
I have to design a FM LNA with output voltage regulation.
The specs are:
output voltage of amplifier between 90 to 105dBuV for an input level from (90-amplifier gain) to 120dBuV.
Does anybody know how can I design this control?
At the moment I have a FM non regulated amplifier. Is there any way to add the regulation to this design?
Thanks a lot!





RE: FM LNA with output voltage regulated
RE: FM LNA with output voltage regulated
I was thinking using a T-attenuator with pin diodes. Any ideas on a concrete part for the level detector?
Thanks
RE: FM LNA with output voltage regulated
If you can get a diode limiter to meet your specs you'll have a cheaper solution. Are you in a 50 ohm system? If so your rms voltage (180 mV) is a bit low for a diode limiter.
RE: FM LNA with output voltage regulated
RE: FM LNA with output voltage regulated
Yes I´m working in a 50R system. I have designed a non-regulated FM amplifier and now I need to add a block that limits the output. This block needs to be the simpler the better, as this is for an automotive application and cost is critical.
OIP3 is around 30dBm so linearity is quite important too.
Thanks in advance
RE: FM LNA with output voltage regulated
315, 433, 866, 2400 MHz? Your intermediate frequency?
RE: FM LNA with output voltage regulated
RE: FM LNA with output voltage regulated
Well, sorry for not saying the frequency range.
This is a LNA for commercial FM radio bands in a car receiver. 87-108MHz. This amplifier goes just after the receiver antenna.
I do agree that FM is constant envelope but because the car moves then the amplifier will receive different power levels depending on how close to the emitter the car is. Hence the importance of OIP3.
RE: FM LNA with output voltage regulated
Obviously you can just put a amp chain in there with an AGC, and have a large output stage compression point. However, that will need a lot of supply current which may generate a lot of heat.
I have seen silicon bipolars set up in feedback mode so that the gain is reduced, but the OIP is greatly improved, while drawing little DC current.