RTL-SDR's tuner E4000 Have 6 IF stage, why?

[Seyyed Mohammad]

I'm newbe in RF, Why E4000 tuner in RTL-SDR have 6 stage of gain?
The only reason I can think about is that maybe The earlier stages consume more power, because thy have better noise figure. They've split gain to achieve balance between current consumption and noise. But it seems 6 stage is really overkill, doesn't it?

And the image of stages has been attached.

[radiolistener]

IFstg1 to compensate loss on RF filter, mixer and mixer filter.
IFstg2, IFstg3, IFstg4 to compensate loss on IF RC filter.
IFstg5, IFstg6 to compensate loss on IF filter.

It combines several PGA in series in order to provide more possible gain levels.

But it seems 6 stage is really overkill, doesn't it?

if you remove IFstg6, it will allow max gain on IFstg5 as 15 dB. With IFstg5 and IFstg6 it provides gain setting up to 30 dB (15 dB + 15 dB).

Using two 15 dB amplifiers in series instead of one for 30 dB allows to get more stable circuit, because amplifier with very high gain is more vulnerable to instability due to possible self-oscillations which may happens due to parasitic feedback.

[MarkT]

I think the basic reason is linearity, this isn't an FM front end, its a realtively wide bandwidth amp to drive an ADC, everything needs to be as linear as possible, so feedback is used limiting each stage's gain (also keeps frequency response wide and flat).