- contributing to the overall NF, thereby allowing for IP3 lation and demodulation schemes are possible. However, to be carefully balanced against NF. Software defined radio CHAPTER 2.3 By contrast, in an SDR many of the intermediate stages the signal chain. Because the gain is limited, the noise floor have been eliminated because sampling occurs as close to of the receiver becomes limited by that of the data the antenna as possible. Since most SDR applications are converter. also wideband, there are no channel filters, thereby allowing many of the neighboring signals to also pass the Tradeoffs versus converter resolution signal chain. Because all of the conversion gain must occur In a traditional receiver, if the signal level was not large in the presence of many signals, intermodulation perfor- enough to be adequately detected by the ADC, then mance is inherently more important. additional gain is used to boost the level above the ADC In a transmitter with multistage up-conversion, the issues are very similar to the super-heterodyne receiver noise floor using an AGC topology. However, it is just as valid to lower the noise floor of the converter. There are above. As with receivers, both noise and intermodulation several ways to do this, as discussed in what follows. The are very important specifications. However, the active easiest thing to do is just specify a converter with more dynamic range of most transmit requirements are only on bits. Unfortunately, the more bits a converter has, the the order of 60 to 70 dB, whereas most receivers require 100 dB or more of dynamic range. The real difficulty of more expensive it is and the more power it dissipates. Therefore, balancing the conversion gain and converter the transmit signal path is maintaining the noise and linearity performance in the RF power amplifiers when resolution is a very important task: too much gain and the ADC is overdriven; too little gain and the ADC directly the power level reaches several hundred or even several sets the noise floor, which 