ignals. The lower its NF, the less it degrades the overall NF of the receiver based on the cascaded NF concept. The second RF filter is a narrowband filter prior to the mixer typically a surface acoustic wave (SAW) type. It suppresses nearby OOB interferers at the mixer image locations (mfLo +1 nfRF) that would fall into the IF pass- band. The mixer translates the RF signal to IF frequencies. The RF and LO signals mix to produce a difference frequency known as IF frequency (fif = |frf-flo|). The undesired spurs and images (e.g., a half-IF) need to be filtered out either before or after the mixer stage. It also can be used to convert the single-ended input signal to a differential signal for the ADC. The LO is tuned to the desired frequency spacing above or below the RF signal and is injected into the mixer. In a direct RF-sampling receiver, the LO essentially turns into the ADC's sampling clock. However, similar to the IF-sampling converter, the RF ADC clock also requires very good phase noise properties. The IF amplifier adds gain to the input signal by reduc- ing the ADC's impact to the receiver NF. Moreover, it compensates for the BPF attenua- tion. It can also be used as a buffer to drive the ADC's capacitive load. In many cases, this stage has multiple gain steps that are digitally controlled to provide an automated gain control loop, which enhances the system's dynamic range. The anti-aliasing filter limits noise and distortion contribution from the IF amplifier. More importantly, it filters the ADC's alias bands. This filter may need a sharp roll-off. The implementation is more feasible at IF than RF frequencies because the ratio of alias frequency to the desired sig- nal is larger. Thus aliasing frequencies are further away from the filter cutoff frequency. The ADC digitizes the input signal. It needs a fast sampling rate to accommodate the fil- ter roll-offs, typically at least three to five times the signal bandwidth. Its SNR needs to be good to ensure minimal impact on the receiver noise figure. The SF