ets of the potential images either in the mixing process or the sampling converters. Since data sheets cannot fully represent the process. In mixer stages, care must be taken to suppress actual performance of a data converter, it is always best the undesired mixer images. In the ADC, signals both to take a look at them on the bench in an environment above and below the desired band may be sampled and similar to that of the end product. aliased into the usable spectrum of the ADC. For either Because data converters are somewhere between the mixer images or aliased signals within the ADC, these digital and analog domains, they are often poorly un- signals must be filtered SO that they are below the min- derstood by both the analog designer and the digital de- imum detectable signal. If they are not, then it is possible signer. For this reason, their effects on transceiver design that they will overpower the desired signal. In the case of are often overestimated, underestimated, or both in the ADC, this required rejection must be achieved different areas. The next few topics will sort through before the aliasing becomes critical. As shown in many of the issues to help determine exactly how con- Figure 2.3-11, the full rejection of the undesired signals verter performance determines performance. Fundamental located between 2nd harmonics located 7.68 & 15.36 between 15.36 & 30.72 MHz 3rd harmonics aliased between 15.36 & 30.72 MHz 15.36 23.04 30.72 Figure 2.3-10 Aliased wideband signal and harmonics. CHAPTER 2.3 Software defined radio Filter Transition Signal rejection must be complete before the images alias upon active spectrum Figure 2.3-11 Aliased transition bands. General converter requirements This number is usually determined by solving Equation (2.3.6) for N, the number of bits. While an effective Bits and noise and a little signal bits measurement is a convenient comparison tool, it has limited usefulness in radio design. SNR is a better The number of converter bits is the most visible speci- tool because of 