Z87200 datasheet(2/54 Pages) ZILOG

2 / 54 page

Z87200

Spread-Spectrum Transceiver

Zilog

4-2

DS96WRL0400

GENERAL DESCRIPTION (Continued)

tal-to-analog conversion (or, if preferred, the spread base-

band signal may be output to an external modulator).

These transceiver functions have been designed and inte-

grated for the transmission and reception of bursts of

spread data. In particular, the PN Matched Filter has two

distinct PN coefficient registers (rather than a single one)

in order to speed and improve signal acquisition perfor-

mance by automatically switching from one to the other

upon signal acquisition. The Z87200 is thus optimized to

provide reliable, high-speed wireless data communica-

tions.

Symbol-Synchronous PN Modulation

The Z87200 operates with symbol-synchronous PN mod-

ulation in both transmit and receive modes. Symbol-syn-

chronous PN modulation refers to operation where the PN

code is aligned with the symbol transitions and repeats

once per symbol. By synchronizing a full PN code cycle

over a symbol duration, acquisition of the PN code at the

receiver simultaneously provides symbol synchronization,

thereby significantly improving overall acquisition time.

As a result of the Z87200's symbol-synchronous PN mod-

ulation, the data rate is defined by the PN chip rate and

length of the PN code; that is, by the number of chips per

symbol, where a “chip” is a single “bit” of the PN code. The

PN chip rate, Rc chips/second, is programmable to as

much as 1/4 the rate of RXIFCLK, and the PN code length,

N, can be programmed up to a value of 64. When operat-

ing with BPSK modulation, the data rate for a PN code of

length N and PN chip rate RC chips/sec is RC/N bps. When

operating with QPSK modulation (or

π/4 QPSK with an ex-

ternal modulator), two bits of data are transmitted per sym-

bol, and the data rate for a PN code of length N and PN

chip rate Rc chips/sec is 2Rc/N bps. Conversely, for a giv-

en data rate Rb bps, the length N of the PN code defines

the PN chip rate Rc as N x Rb chips/sec for BPSK or as (N

x Rb)/2 chips/sec for QPSK.

The data rate Rb and the PN code length N, however, can-

not generally be arbitrarily chosen. United States FCC Part

15.247 regulations require a minimum processing gain of

10 dB for unlicensed operation in the Industrial, Scientific,

and Medical (ISM) bands, implying that the value of N must

be at least 10. To implement such a short code, a Barker

code of length 11 would typically be used in order to obtain

desirable auto- and cross-correlation properties, although

compliance with FCC regulations depends upon the over-

all system implementation. The Z87200 further includes

transmit and receive code overlay generators to insure

that signals spread with such a short PN code length pos-

sess the spectral properties required by FCC regulations.

The receiver clock rate established by RXIFCLK must be

at least four times the receive PN spreading rate and is lim-

ited to a maximum speed of 45.056 MHz in the 45 MHz

Z87200 and 20.0 MHz in the 20 MHz Z87200. The ensuing

discussion is in terms of the 45 MHz Z87200, but the nu-

merical values may be scaled proportionately for the 20

MHz version. As a result of the maximum 45.056 MHz RX-

IFCLK, the maximum supported PN chip rate is 11.264

Mchips/second. When operating with BPSK modulation,

the maximum data rate for a PN code of length N is

11.264/N Mbps. When operating with QPSK modulation

(or

π/4 QPSK with an external modulator), two bits of data

are transmitted per symbol, and the data rate for a PN

code of length N is 22.528/N Mbps. Conversely, for a given

data rate Rb, the length N of the PN code employed must

be such that the product of N x Rb is less than 11.264

Mchips/sec (for BPSK) or 22.528 Mchips/sec (for QPSK).

For the 45 MHz Z87200, then, a PN code length of 11 im-

plies that the maximum data rate that can be supported in

compliance with the processing gain requirements of FCC

regulations is 2.048 Mbps using differential QPSK. Note

again, however, that FCC compliance using the Z87200

with a PN code of length 11 depends upon the overall sys-

tem implementation.

Z87200 Datasheet(PDF) 2 Page - Zilog, Inc.

Z87200 Datasheet(HTML) 2 Page - Zilog, Inc.

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

Datasheet Download

Link URL