The cascaded noise figure is a figure of merit for an RF system that determines the degradation of SNR from input to output. If 4 blocks were connected in series, ->B1->B2->B3->B4-> the cascaded noise figure would be calculated as F = F1+(F2-1)/G1+(F3-1)/(G1+G2)+(F4-1)/(G1+G2+G3) where G is the Gain in dB and F is the noise Figure of each respective block. From this formula we can see that the majority of noise figure in a cascaded system is attributed to the first block in the cascade and to the extent that this block has high gain, any downstream components will not have as significant of effect on the cascaded noise figure. This is why typically a LNA is used as the B1 block in a RF receiver.
Triad designs many low noise systems and fully leverages the cascaded noise figure to yield low noise systems in our designs. This may lead to a system partitioning strategy where some blocks in the system are left off chip in specialized processes while others are integrated. A Triad Mixed Signal Integration Architect may greatly assist in making these architectural decisions for your custom ASIC design.