參數(shù)資料
型號(hào)： HFA3860AIV96
廠商： INTERSIL CORP
元件分類： 無繩電話/電話
英文描述： Circular Connector; No. of Contacts:5; Series:MS27473; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:10; Circular Contact Gender:Pin; Circular Shell Style:Straight Plug; Insert Arrangement:10-5 RoHS Compliant: No
中文描述： TELECOM, CELLULAR, BASEBAND CIRCUIT, PQFP48
封裝： 7 X 7 X 1 MM, PLASTIC, TQFP-48
文件頁(yè)數(shù)： 16/39頁(yè)
文件大?。?/td> 251K
代理商： HFA3860AIV96
2-146
conditions. The CCA in combination with the visibility of the
various internal parameters (i.e., Energy Detection measure-
ment results), can assist an external processor in executing
algorithms that can adapt to the environment. These algo-
rithms can increase network throughput by minimizing
collisions and reducing transmissions liable to errors.
There are two measures that are used in the CCA assessment.
The receive signal strength (RSSI) which measures the energy
at the antenna and carrier sense early (CSE). Both indicators
are normally used since interference can trigger the signal
strength indication, but it might not trigger the carrier sense.
The carrier sense, however, becomes active only when a
spread signal with the proper PN code has been detected, so it
may not be adequate in itself. The CCA compares these
measures to thresholds at the end of the first antenna dwell
following RX_PE going active. “The state of CCA is not
guaranteed from the time RX_PE goes high until the CCA
assessment is made. At the end of a packet, after RX_PE has
been deasserted, the state of CCA is also not guaranteed.”
CCA should be sampled 16
μ
s after raising RX_PE.
The receive signal strength indication (RSSI) measurement
is an analog input to the HFA3860A from the successive IF
stage of the radio. The RSSI A/D converts it within the
baseband processor and it compares it to a programmable
threshold. This threshold is normally set to between -70 and
-80dBm. A MAC controlled calibration procedure can be
used to optimize this threshold.
The CSE (Carrier Sense Early) is a signal that goes active
when SQ1 (after an antenna dwell) has been satisfied. It is
called early, since it is indicated before the carrier sense
used for acquisition. It is calculated on the basis of the
integrated energy in the correlator output over a block of 15
symbols. Thus, the CCA is valid after 16
μ
s has transpired
from the time RX_PE was raised.
The Configuration registers effecting the CCA algorithm
operation are summarized below (more programming details
on these registers can be found under the Control Registers
section of this document).
The CCA output from pin 32 of the device can be defined as
active high or active low through CR 1 (bit 5). The RSSI
threshold is set through CR14. If the actual RSSI value from
the A/D exceeds this threshold then ED becomes active.
The instantaneous RSSI value can be monitored by the
external network processor by reading the test bus in mode 3.
It measures the signal 16
μ
s after the start of each antenna or
data dwell. RSSI value is invalid after MD_RDY goes active if
CR31 bit 1 is set to a “1”. Value is valid until MD_RDY drops if
bit is set to a “0”. The programmable threshold on the CSE
measurement is set through CR12 and CR13. More details on
SQ1 are included in the receiver section of this document.
In a typical single antenna system CCA will be monitored to
determine when the channel is clear. Once the channel is
detected busy, CCA should be checked periodically to
determine if the channel becomes clear. CCA is stable to
allow asynchronous sampling or even falling edge detection of
CCA. Once MD_RDY goes active, CCA is then ignored for the
remainder of the message. Failure to monitor CCA until
MD_RDY goes active (or use of a time-out circuit) could result
in a stalled system as it is possible for the channel to be busy
and then become clear without an MD_RDY occurring.
A Dual antenna system has the added complexity that CCA will
potentially toggle between active and inactive as each antenna
is checked. The user must avoid mistaking the inactive CCA
signal as an indication the channel is clear. A time-out circuit
that begins with the first busy channel indication could be used.
Alternatively CCA could be monitored, a clear channel
indication for 2 successive antenna dwells would show the
channel clear on both antennas. Time alignment of CCA
monitoring with the receivers 16
μ
s antenna dwells would be
required. Once the receiver has acquired, CCA should be
monitored for loss of signal until MD_RDY goes active.
An optional CCA mode is set by CR31 bit 0. When set to a
zero, the HFA3860A will perform the CCA monitoring for
successive antenna dwells when dual antenna mode is
selected. The external CCA signal will go active when a busy
channel is detected, CCA will stay active until the channel
shows clear for two successive antenna dwells. This allows
the same simple algorithm to be used in both signal and dual
antenna, namely, continuous monitoring of CCA for a clear
channel until MD_RDY goes active.
CR5 selects the starting antenna used when RXPE is
brought active.
CSE is updated at the end of each antenna dwell. After
acquisition, CSE is updated every 64 symbols. In the event
of signal loss after acquisition, CSE may go inactive. But
because the accumulation is over 63 symbols instead of 15,
it is more likely the SQ1 value will exceed the CSE threshold
and CSE will remain active.
Demodulator Description
The receiver portion of the baseband processor, performs
A/D conversion and demodulation of the spread spectrum
signal. It correlates the PN spread symbols, then
demodulates the DBPSK, DQPSK, BMBOK, or QMBOK
symbols. The demodulator includes a frequency tracking
loop that tracks and removes the carrier frequency offset. In
addition it tracks the symbol timing, and differentially
decodes (where appropriate) and descrambles the data. The
data is output through the RX Port to the external processor.
The PRISM baseband processor, HFA3860A uses differential
demodulation for the initial acquisition portion of the message
processing and then switches to coherent demodulation for
the rest of the acquisition and data demodulation. The
HFA3860A is designed to achieve rapid settling of the carrier
tracking loop during acquisition. Rapid phase fluctuations are
HFA3860A
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