uency. As with the receive mixer/demodulator, it integration technology improves, multi-carrier direct may be desirable to change the bias levels or the drive level conversion may become a possibility; however, such of the data or LO levels to optimize distortion. a transmit configuration requires sideband suppression As with the receive LO, the transmit LO is variable in that is about 15 dB better than the spurious requirements frequency and easily programmable via software control to prevent images on one side of the center frequency using PLL or DDS techniques. Here too, it may be de- from overpowering a potentially weak carrier on the other. sirable to change the LO drive level to optimize spurious In either application, a DSP or baseband ASIC is used performance under a variety of signal conditions. As with to generate the modulated baseband data. This data is fed the single-band operation of the receiver, there may be either directly to a pair of baseband DACs (I and Q) for cases where a fixed LO is required. Such an example direct RF modulation or to a digital processor responsible would be for operation within a single band where tuning for digitally translating them to a suitable digital IF. is accomplished within the transmit signal processor Depending on the application, the DSP alone or in con- (TSP), DUC, or FPGA. junction with a digital processor can be used to digitally As with the receive path, the data converter or DAC is pre-distort the baseband data in such a manner that often the bottleneck. However, since dynamic range re- distortion products generated later in the signal chain will quirements for the transmit signal path are much lower be cancelled. (typically 25 to 45 dB) than the receive path, component If an IF stage is employed, the baseband data gener- selection is not quite as difficult. Many DACs are avail- ated by the DSP must be up-converted either digitally able that facilitate a wide range of adjustments, including with an FPGA or ASIC (also known as TSPs or DUCs) or gain and offs