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HSP50214AVC

Programmable Downconverter

Intersil 

HSP50214A

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

DQPSK

CHANNEL RATE (Kbps) 270.8

270.8

48.6

CONTROL GMSK

MODULATION

GMSK

π/4

DQPSK

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 approxi-

mately 1.2288MHz wide with many spread spectrum chan-

nel in the band. The PDC supplies the downconversion and

filtering required to receive a single RF channel in the pres-

ence of strong adjacent interference. 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 half-

band and 255-tap programmable, 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 an 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 (for continuous PSK signals - not

burst).

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.

Resampling and Interpolation Filters

Two key features of the resampling FIR filter are that the res-

ampler filter allows the output sample rate to be programmed

with millihertz resolution and that the output sample rate can

be phase locked to an independent separate clock. The res-

ampler 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 applications 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 output when nar-

row frequency bands are being processed. The increase in

output rate allows maximum use of the programmable 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, providing over 84dB of dynamic

range. The 18 bits of resolution on the internal references

provide a spurious floor that is better than 98dBc. Further-

more, the PDC provides up to 42dB of gain scaling to com-

pensate 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 maxi-

mizes the output resolution for small signals and compen-

sates for changes in the RF front end gain, to handle

changes in the incoming signal.

7

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