Design and implementation of digitalized IF multi-carrier transmitter based on AD6623

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Software Radio, a systematic structure to realize wireless communication launched in recent years, is a significant breakthrough in the field of wireless communication in the wake of analog to digital communication, fixed to mobile communication. The basic principle of it is that the received analog signal is digitalized as soon as possible, and various functions of the radio are realized by software to the most extent.

Software Radio is an open structure to realize all types of wireless communication systems through a general hardware platform and then through software loading. For Software Radio, the digitalized hardware platform is the basis, the programmable and reusable software is the core, and realizing multi-band,  multi-system, and universal reception is the goal. Figure 1 is the block diagram to realize Software Radio.

Figure 1 shows the four-carrier communication system. The traditional simulation structure completes the conversion from RF(Radio Frequency) to IF(Intermediate Frequency) and the conversion from IF to RF. In the stage of receiving IF, AD6644/AD6645 sample the intermediate frequency, AD6624(four-channel receive signal processor) completes digital tuning and filtering, and abstracts the data to baseband. In the stage of transmitting IF, AD6623(four-channel transmit signal processor) complete FIR filtering, digital frequency conversion, and the integration of four carrier signals, and AD9772 complete the 14 digital-to-analog conversions.  The key point to process the multi-rate signals in digital intermediate frequency is choosing appropriate abstraction, filter coefficiency. If the digitalization of signals at the end of a radio frequency is realized, the existed component can not meet the requirements of the later procession. At present, we generally carry out the plan of IF digitalization. The back-end IF digital signal processing unit adopts reconfigurable devices to complete the signal procession. The system remains the characteristics of common use, flexibility, and openness of the Software Radio Receiver.

                                    The block diagram to realize Software Radio

The introduction of the function of AD6623

104MSPS four-channel radio signal transmission processor AD6623 is a kind of digital processor that can complete data interpolation, pulse shaping, filtering, diverse modulation, and frequency tuning. 

Each channel has an independent interpolation filter and control unit, and each chip generates four carriers. The interpolation filter is programmed by users, RCF (or each modulation type) coefficiency can also be programmed, allowing users to stipulate the number of taps of the filter needed. In-phase and quadrature sampling control are processed by the digital filters in TSP, such as CIC and RAM RCF. These filters interpolate the I and Q data to eliminate signal interference, signal aliasing, and Image signal component.

AD6623 features multiple carriers, modulation types. The main function of AD6623 is to transmit the baseband digital signal generated by DSP to a digital-to-analog converter with the characteristics of high sampling rate, wide analog bandwidth, and wide dynamic range through interpolation and digital frequency conversion. By this procession, it completes bandwidth digital up-conversion. It is widely used by the digital transceivers in Cellular base station, Micro/Pico Cell base station, multi-carrier, and multi-mode base station (such as GSM, EDGE, IS136, PHS, IS95, CDMA, UMTS, and CDMA2000).

Please click here to learn more information about AD6623ASZ.

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