Help!low noise VGA with 40MHz~90MHz bandwidth, 32dB gain range with 0.5dB gain step

[purian]

Hello, I'm a fresher about analog and RF design, i want to design a VGA, the noise figure below 10dB, and the bandwidth is 40MHz~90MHz, the gain range is 32dB(-32dB to 0dB or 32dB to 0dB, is there any difference) with the gain step is about 0.5dB, and also with good linearity. which structure of the VGA can be used to reach the spec, how can i trade off between the noise, gain, linearity, and the bandwidth. Are there any good suggestions?

Thank you all !
Purian

 

[Darktrax]

The frequency range is on the border between what can be done with a high frequency op-amp like some video drivers, and a RF amplifier with a controlled attenuator, or maybe ALC loop.

Provided the power level is not so high that heat dissipation becomes a problem, a wide-band RF amplifier with a PIN diode attenuator on the output, would do it. Attenuation before the amplifier is not an option because the attenuation value adds directly to the noise figure.

Nicer is to sample the level at the output, and have it drive an ALC loop. There are lots of nice devices made for exactly this. I am sure that there are other very good brands, but simply because it was the first one I thought of, try this

--> LINK to VGAs from Analog

That is a 75MHz wide bandwidth reference circuit. Have a look at the rest of the list.

--> VGA List

Consider brands like Avago, Maxim, Linear, and many others. Not to show favorites, I think others in this forum might provide suggestions.