HSP50214 데이터 시트보기 (PDF) - Intersil
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HSP50214 Datasheet PDF : 54 Pages
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HSP50214
TABLE 2. CELLULAR BASESTATION APPLICATIONS USING
TDMA
STANDARD
GSM
PCN
IS-54
TYPE Cellular
Cellular
Cellular
BASESTATION RX 935-960 1805-1880 824-849
BAND (MHz)
CHANNEL BW (kHz) 200
200
30
# TRAFFIC CHANNELS
8
16
3
VOICE MODULATION GMSK
GMSK
π/4
DPSK
CHANNEL RATE (Kbps) 270.8
270.8
48.6
CONTROL GMSK
MODULATION
GMSK
π/4
DPSK
CHANNEL RATE (Kbps) 270.8
270.8
48.6
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.
7
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