bt8970 Mindspeed Technologies, bt8970 Datasheet - Page 26

• Manufacturer Part Number: bt8970
• Description: Single-chip Hdsl Transceiver
• Manufacturer: Mindspeed Technologies

2.0 Functional Description
2.2 Receive Section
2.2.4.2 Nonlinear Echo Canceller (NEC)
The Nonlinear Echo Canceller (NEC) reduces the residual echo power in the echo canceller output caused by
nonlinear effects in the transmitter DAC, receiver ADC, analog hybrid circuitry, or line cables.
Nonlinear Echo Canceller Mode Register [nonlinear_ec_modes; 0x09]. This allows the NEC to operate on the
peak of the echo regardless of differing delays in the echo path.
coefficient updates only. A special mode exists to zero all of the coefficients; it is also enabled through the
microcomputer interface.
enabled through the microcomputer interface. The 64, 14-bit, individual NEC coefficients can be read and
written through the microcomputer interface. Adaptation should be frozen prior to reading or writing
coefficients.
2.2.5 Equalizer
Four LMS filters are used in the equalizer to process the echo canceller output so that received symbols can be
reliably recovered. The filters are a digital automatic gain controller, a feed forward equalizer, an error
predictor, and a decision feedback equalizer. Their interconnections are shown in
2.2.5.1 Digital Automatic Gain Control (DAGC)
The Digital Automatic Gain Control (DAGC) scales the echo-free signal to the optimum magnitude for
subsequent processing. Its structure is that of an LMS filter, but it is a degenerate case because there is only one
tap.
coefficient update only.
be frozen prior to reading or writing the coefficient.
2.2.5.2 Feed Forward Equalizer (FFE)
The Feed Forward Equalizer (FFE) removes precursors from the received signal. The FFE may be operated in a
special adapt last mode. In this mode, which is useful during startup, only the last coefficient is updated. The
last coefficient is the one which is multiplied with the oldest data sample (sample #7).
coefficient updates only. A special mode exists to zero all of the coefficients; it is also enabled through the
microcomputer interface. Individual FFE coefficients can be read and written through the microcomputer
interface. Adaptation should be frozen prior to reading or writing coefficients.
2.2.5.3 Error Predictor (EP)
The Error Predictor (EP) improves the performance of the equalizer by prognosticating errors before they occur.
A freeze coefficient mode may be specified via the microcomputer interface. This mode disables the coefficient
updates only. A special mode exists to zero all of the coefficients; it is also enabled through the microcomputer
interface. Individual EP coefficients can be read and written through the microcomputer interface. Adaptation
should be frozen prior to reading or writing coefficients.
2.2.5.4 Decision Feedback Equalizer (DFE)
The Decision Feedback Equalizer (DFE) removes postcursors from the received signal. A freeze coefficient
mode may be specified via the microcomputer interface. This mode disables the coefficient updates only. A
zero coefficients mode exists to zero all of the coefficients; it is also enabled through the microcomputer
interface. A zero filter output mode exists to zero the output of the FIR with no effect on the coefficients. It is
also enabled through the microcomputer interface. Individual DFE coefficients can be read and written through
the microcomputer interface. Adaptation should be frozen prior to reading or writing coefficients.
2-8
The delay of the transmit-symbol input to the NEC can be specified via the microcomputer interface,
A freeze coefficient mode may be specified via the microcomputer interface. This mode disables the
An additional mode exists to zero the output of the look-up table with no effect on the coefficients. It is also
A freeze coefficient mode may be specified via the microcomputer interface. This mode disables the
The DAGC gain coefficient can be read or written through the microcomputer interface. Adaptation should
A freeze coefficient mode may be specified via the microcomputer interface. This mode disables the
Preliminary Information/Conexant Proprietary and Confidential
Conexant
Figure
Single-Chip HDSL Transceiver
2-3.
100101B
Bt8970