HFA3860 datasheet(13/40 Pages) INTERSIL

13 / 40 page

Table 7 shows examples of the bit rates and the symbol

rates and Figure 8 shows the modulation schemes.

The modulator is completely independent from the

demodulator, allowing the PRISM baseband processor to be

used in full duplex operation.

Header/Packet Description

The HFA3860 is designed to handle continuous or

packetized Direct Sequence Spread Spectrum (DSSS) data

transmissions. The HFA3860 generates its own preamble

and header information.

The device uses a synchronization preamble of up to 256

symbols, and a header that includes ﬁve ﬁelds. The

preamble is all 1's (before entering the scrambler). The

actual transmitted pattern of the preamble will be

randomized by the scrambler. The preamble is always

transmitted as a DBPSK waveform.

The ﬁve ﬁelds for the header shown in Figure 9 are:

Start Frame Delimiter (SFD) Field (16 Bits) - This

ﬁeld

carries the synchronization to establish the link frame timing.

The HFA3860 will not declare a valid data packet, even if it

PN acquires, unless it detects the SFD. The HFA3860

receiver is programmed to time out searching for the SFD via

CR15. The timer starts counting the moment that initial PN

synchronization has been established from the preamble.

Signal Field (8 Bits) - This ﬁeld indicates what data rate the

data packet that follows the header will be. The HFA3860

receiver looks at the signal ﬁeld to determine whether it

needs to switch from DBPSK demodulation into DQPSK or

B/QMBOK demodulation at the end of the always DBPSK

preamble and header ﬁelds.

Service Field (8 Bits) - This ﬁeld is currently unassigned

and can be utilized as required by the user. Set to 00h for

TABLE 7. BIT RATE TABLE EXAMPLES FOR MCLK = 44MHz

DATA

MODULATION

A/D SAMPLE CLOCK

(MHZ)

TX SETUP CR 20

BITS 1, 0

RX STATUS CR 24

BITS 7, 6

DATA RATE (Mbps)

SYMBOL RATE

(MSPS)

DBPSK

DQPSK

BMBOK

5.5

1.375

QMBOK

1.375

802.11 DSSS BPSK

802.11 DSSS QPSK

5.5 MB/S BMBOK

11 MB/S QMBOK

1 MB/S

BARKER

2 MB/S

BARKER

DATA

IOUT

QOUT

CHIP

RATE

1 BIT ENCODED TO ONE OF

2 CODE WORDS

2 BITS ENCODED

4 CODE WORDS

4 BITS ENCODED TO ONE OF

16 MODIFIED WALSH

CODE WORDS

8 BITS ENCODED TO

256 MODIFIED WALSH

CODE WORDS

SYMBOL

RATE

I vs Q

11 MC/S

1 MS/S

1.375 MS/S

11 CHIPS

8 CHIPS

MODIFIED

(TRUE/INVERSE)

TO ONE OF

FIGURE 8. MODULATION MODES

WALSH FUNCTIONS

ONE OF

HFA3860

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