RS8973 Mindspeed Technologies, RS8973 Datasheet - Page 36

• Manufacturer Part Number: RS8973
• Description: Single-chip Sdsl/hdsl Transceiver
• Manufacturer: Mindspeed Technologies

2.0 Functional Description
2.2 Receive Section
2-12
Noise Level Histogram Meter
2.2.7.6 Detector Meters
2.2.7.5 Sync Detector
Symbol Histogrammer
Noise Level Meter
SNR Alarm
BER Meter
The sync detector compares the output of the scrambler with the output of the
symbol detector. The number of equivalent bits is accumulated for 128
comparisons. The result is then compared to a Scrambler Synchronization
Threshold Register [scr_sync_th; 0x2E], a lock is declared, and the sync bit of the
irq_source register is set if the count is greater than the threshold. For a count less
than or equal to the threshold, no lock condition is declared and the sync bit is
unaffected.
The detector consists of five meters: a BER meter, a symbol histogrammer, a
noise-level meter, a noise-level histogram meter, and an SNR alarm meter.
The BER meter provides an estimate of the bit error rate when the received
symbols are known to be scrambled 1s. When the LFSR is operating as a
descrambler, the meter counts the number of 1s on the descrambler output. When
the LFSR is operating as a scrambler, the BER meter counts the number of equal
scrambler and symbol detector outputs. The counter operates over the meter timer
interval [meter_low, meter_high; 0x18, 0x19]. The counter is saturated to 16 bits.
At the end of the measurement interval the counter is loaded into the Bit Error
Rate Meter Registers [ber_meter_low, ber_meter_high; 0x4C, 0x4D].
The symbol histogrammer computes a coarse histogram of the received symbols.
It operates by counting the number of 1s received during the meter timer interval
[meter_low, meter_high; 0x18, 0x19]. That is, at the start of the measurement
interval a counter is cleared. For each detector output which is + 1 or – 1, the
counter is incremented. If the detector output is + 3 or – 3, the count is held at its
previous value. The count is saturated to 16 bits. At the end of the measurement
interval, the 8 MSBs of the counter are loaded into the Symbol Histogram Meter
Register [symbol_histogram; 0x4E]. This can be used during start-up to detect the
transition from two-level to four-level signalling.
The noise level meter estimates the noise at the input to the slicer. It operates by
accumulating the absolute value of the slicer error over meter timer interval
[meter_low, meter_high; 0x18, 0x19]. At the end of the measurement interval, the
16 MSBs of the 32-bit accumulator are loaded into the Noise Level Meter
Register [nlm_low, nlm_high; 0x50, 0x51].
The noise level histogram meter counts the number of high noise-level conditions
which occur during each meter countdown interval. A high noise-level condition
is defined as the absolute value of the slicer error signal exceeding the threshold
specified in the noise level histogram threshold register [0x2A,2B].
The SNR alarm provides a rapid indication of impulse noise disturbances and loss
of signal so that corrective action can be taken. The alarm is based on a second
noise level meter. The meter is the same as the preceding noise level meter except
it operates on a dedicated timer, the SNR alarm timer. The absolute value of the
slicer error is accumulated during the timer period. At the end of the
measurement interval, the 16 MSBs of the accumulator are compared against the
SNR Alarm Threshold Register [snr_alarm_th_low, snr_alarm_th_high; 0x34,
0x35]. If the result is greater than this threshold, an interrupt is set in the
irq_source register. The threshold is set through the MCI.
Preliminary Information
Conexant
Single-Chip SDSL/HDSL Transceiver
N8973DSD
RS8973