SS1102C datasheet(42/129 Pages) ETC1

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Direct Sequence Spread Spectrum Baseband Modem (SSTM)

PRELIMINARY V1.8

12. Direct Sequence Spread Spectrum Baseband

Modem (SSTM)

The SSTM is a low-power, multi-purpose communication module designed to support

spread spectrum data communications. The SSTM contains all the baseband function

required for an FCC Part 15 compliant device.

The SSTM supports both full-duplex and half-duplex operations in synchronous mode.

In the half-duplex, no assumption about higher level protocols is made. Instead, the

SSTM is designed to be flexible and can be configured for a variety of uses.

In full-duplex operation communication is achieved by using a time-division duplex

(TDD) protocol and burst structure. The SSTM supports full-duplex data rates up to

64Kbps and half-duplex data rates up to 166 Kbps.

The SSTM is made up of five functional modules. These include the receiver, the

transmitter, the time-division duplex (TDD) controller, the transmit and receive FIFOs,

and the master clock generator.

12.1.

Receiver

The receiver module performs all the digital signal processing required by the spread

spectrum receiver, including de-correlation and demodulation.

The receiver samples the incoming baseband signal at two samples per PN chip. The

samples are correlated with four possible PN sequences in 64-bit parallel correlators.

The de-correlated signal is demodulated via a digital phase locked loop. To reduce

power consumption, the receiver is powered down while the SSTM is transmitting and

consumes peak power only during the brief period of initial acquisition. After

acquisition, the receiver goes into tracking/detection mode, where the power

consumption of the receiver module is reduced by two orders of magnitude.

12.2.

Transmitter

The transmit module generates the spread spectrum binary sequence for output to the

RF modulator.

The transmitter logic encodes two consecutive bits of data into one of four possible 32-

bit PN sequences. The transmitted PN sequence is further randomized by modulus-2

addition with a fixed 2047-bit long PN sequence. This operation smooths the output

spectrum of the transmitted signal and eliminates discrete spectral components. During

TDD operation, the transmitter is powered off during the portion of the cycle when the

SSTM is in receive mode in order to save power. The transmitter output is at high-

impedance state during a receiving period.

SS1102C Datasheet(PDF) 42 Page - List of Unclassifed Manufacturers