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HSP50214VC Datasheet(PDF) 7 Page - Intersil Corporation |
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HSP50214VC Datasheet(HTML) 7 Page - Intersil Corporation |
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7 / 54 page  7 Several applications are combinations of frequency and time domain multiple access schemes. For example, GSM is a TDMA signal that is frequency hopped. The individual chan- nels contain Gaussian MSK modulated signals. The PDC again offers the 0.012Hz tuning resolution for de-hopping the received signal. The combination of halfband and 256-tap programmable, 22-bit coefficient FIR filters readily performs the necessary matched filtering for demodulation and opti- mum detection of the GMSK signals. CDMA Based Standards and Applications For Code Division Multiple Access (CDMA) type signals, the PDC offers the ability to have a single wideband RF front end, from which it can select a single spread channel of interest. The synchronization circuitry provides for easy con- trol of multiple PDC for applications where multiple received signals are required, such as base-stations. In IS-95 CDMA, the receive signal bandwidth is 1.2288MHz wide with many spread spectrum channel in the band. Each spread channel is a QPSK signal. The PDC supplies the downconversion and filtering required to receive a single spread channel in the presence of strong adjacent interfer- ence. Multiple PDC’s would be sourced from a single receive RF chain, each processing a different receive frequency channel. The despreader would usually follow the PDC. In some very specific applications, with short, fixed codes, the filtering and despreading may be possible with innovative use of the programmable, 22-bit coefficient FIR filter. The PDC offers 0.012Hz resolution on tuning to the desired receive channel and excellent rejection of the portions of the band not being processed, via the halfband and 255-tap pro- grammable, 22-bit coefficient FIR filter. Traditional Modulation Formats AM, ASK, FM and FSK The PDC has the capability to fully demodulate AM and FM modulated waveforms. The PDC outputs 15 bits of amplitude or 16 bits of frequency for these modulation formats. The FM dis- criminator has a 63-tap programmable, 22-bit coefficient FIR fil- ter for additional signal conditioning of the FM signal. Digital versions of these formats, ASK and FSK are also readily pro- cessed using the PDC. Just as in the AM modulated case, ASK signals will use 15-bit magnitude output of the Cartesian to Polar Coordinate converter. Multi-tone FSK can be processed several ways. The frequency information out of the discrimina- tor can be used to identify the received tone, or the filter can be used to identify and power detect a specific tone of the received signal. AMPS is an example of a FM application. PM and PSK The PDC provides the downconversion, demodulation, matched filtering and coordinate conversion required for demodulation of PM and PSK modulated waveforms. These modulation formats will require external carrier and symbol timing recovery loop filters to complete the receiver design. The PDC was designed to interface with the HSP50210 Dig- ital Costas Loop to implement the carrier phase and symbol timing recovery loop filters. Digital modulation formats that combine amplitude and phase for symbol mapping, such as m-ary QAM can also be downconverted, demodulated, and matched filtered. The received symbol information is provided with 16 bits of reso- lution in either Cartesian or Polar coordinates to facilitate remapping into bits and to recover the carrier phase. Exter- nal Symbol mapping and Carrier Recovery Loop Filtering is required for this waveform. Re-Sampling and Interpolation Filters Two key features of the re-sampling FIR filter are that the resampler filter allows the output sample rate to be pro- grammed with millihertz resolution and that the output sam- ple rate can be phase locked to an independent separate clock. The resampler frees the front end sampling clocks from having to be synchronous or integrally related in rate to the baseband output. The asynchronous relationship between front end and back end clocks is critical in applica- tions where ISDN interfaces drive the baseband interfaces, but the channel sample rates are not related in any way. The interpolation halfband filters can increase the rate of the out- put when narrow frequency bands are being processed. The increase in output rate allows maximum use of the program- mable FIR while preserving time resolution in the baseband data. 14-Bit Input and Processing Resolution The PDC maintains a minimum of 14 bits of processing reso- lution through to the output. Which provides over 84dB of dynamic range. The 18 bits of resolution on the internal ref- erences provide a spurious floor that is better than 98dBc. Furthermore, the PDC provides up to 42dB of gain scaling to compensate for any change in gain in the RF front end as well as up to 96dB of gain in the internal PDC AGC. This gain maximizes the output resolution for small signals and compensates for changes in the RF front end gain, to handle changes in the incoming signal. TABLE 2. CELLULAR BASESTATION APPLICATIONS USING TDMA STANDARD GSM PCN IS-54 TYPE Cellular Cellular Cellular BASESTATION RX BAND (MHz) 935-960 1805-1880 824-849 CHANNEL BW (kHz) 200 200 30 # TRAFFIC CHANNELS 8163 VOICE MODULATION GMSK GMSK π/4 DPSK CHANNEL RATE (Kbps) 270.8 270.8 48.6 CONTROL MODULATION GMSK GMSK π/4 DPSK CHANNEL RATE (Kbps) 270.8 270.8 48.6 HSP50214 |
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