Help needed to design gain controlled LNA

Hi, wonder if anybody has come across designing a gain controlled LNA with gain of -10dB to 38dB of <=1dB per step. Would appreciate your recommendation on structure and the breakdown of gain & fine tuning method.

Thank you in advance.

Hi,
The DR is 48 dB, Currently no one is giving this much attenuation range.
Max available range is 31dB with 5 bit.
So hava a LNA with a gain of 44dB if 3dB is the IL for two 5 bity 1dB step attenuators.
the gain will be 44-3-3 i.e 38 and can go the attenuation to 38-31-31 i.e. -27dB.

You can have other combinations like 20dB 1 bit attenuator with cascaded 5bit step attenuator.

Hope this helps you

What happens to the Noise figure in this case?wrt to gain variation.

Yes, the noise figure will be changed. The change will be depending on how u allocate the gain attenuation.

Hi, anybody, can recommend structure to use in designing LNA with accurate gain control of the amount of dB as mentioned above?

As i mentioned above, the structure will be 2 or 3 stage LNA ( depending on gain and operating frequency) with 2 stage 5 bit attenuator.

Here are a few example IC's:


http://www.analog.com/en/amplifiers-...cts/index.html

This part has beauty to operate in IF and RF frequency range, has mixer if you interest to use but has less gain from the requirement. So have additional LNA

Hi, kspalla, wonder if u can help to comment on structure of LNA to be used to achieve NF < 2.5dB with the attenuator added on. Currently, had tried to implement a first stage input attenuator in front of an amplifier using resistive feedback structure. The best NF obtainable is about 3dB.

Resistive feedback contribute more noise try reactive like inductive.

Hi, the LNA is operating in VHF/UHF range. The size will be very big if to use inductive matching on chip.

Have you tried what value of inductance (if required).
I mean to say the value lies hardly in few nH. not even tens.
Just try with inductor and see.

Able to get NF ≈ 2.5dB at Max gain by reoptimising the LNA input matching. However, it's quite difficult to maintain the input return loss @ <8dB when the attenuation changed. Any comment?