DR must be suffi- cient SO that spurs caused by in-band and out-of-band interferers do not dominate the overall noise level. When evaluating a transition from an IF-sampling-based to a direct RF-sampling-based receiver design, one must examine the overall impact on the receiver sensitivity, as well as performance in a blocking condition. Since the RF-sampling ADC replaces the signal chain from the mixer onward, the comparisons provided are focused at the mixer input, assuming the same AFE for both designs (see Fig. 5.24). The parameters also can be calculated at the antenna input for a given LNA in the same manner using the respective gains and losses of the amplifier and filters. The receiver sensitivity is a measure of how it can recover and pro- cess very weak input signals. Weak input signals cannot be demodulated, if the receiver noise within the demodulated bandwidth is larger than the received signal itself. The trans- mitter and receiver are often completely independent, thus raising the desired signal ampli- tude above the noise floor is not always possible. The only option to improve receiver 716 Chapter 5 sensitivity is to reduce its noise floor or, in other words, to improve its noise figure. In the sensitivity condition, the receiver operates at the maximum gain. In the presence of a strong blocker/interferer the gain needs to be reduced in order to avoid saturation of the input (desensitization). Therefore, the receiver NF will be much stronger, which impacts the mini- mum signal that can be recovered in a blocking condition. The images from the mixer at mfLo + nfRF can fall into the band of interest that requires adequate filtering at RF level. This ensures that an OOB blocker at the image locations does not generate a mixing product within the desired band. Furthermore, the phase noise of the LO frequency is also mixed with the RF signal (interferer). This increases the noise power with in-band blockers, increasing the amount of noise leaking from the blocker into the wanted carrier bandwidth. The