RS8973 Mindspeed Technologies, RS8973 Datasheet - Page 33

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

RS8973
Single-Chip SDSL/HDSL Transceiver
2.2.5 Echo Canceller
2.2.6 Equalizer
N8973DSD
2.2.5.2 Nonlinear Echo
Automatic Gain Control
2.2.5.1 Linear Echo
Canceller (NEC)
2.2.6.1 Digital
Canceller
The echo canceller (EC) removes images of the transmitted symbols from the
received signal and consists of two blocks: a linear and nonlinear echo canceller.
The organization of the blocks is displayed in
Processing.
The linear echo canceller (LEC) is a conventional LMS, finite impulse response
(FIR) filter, which removes linear images of the transmitted symbols from the
received signal. It consists of a 120-tap FIR filter with 32-bit adapted
coefficients.
specially; the data value is set to a constant 1. This serves to cancel any DC offset
that may be present.
The nonlinear echo canceller (NEC) reduces the residual echo power in the echo
canceller output caused by nonlinear effects in the transmitter, receiver, analog
hybrid circuitry, or line cables.
the MCI, 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.
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
Digital Signal
The digital automatic gain control (DAGC) scales the echo-free signal to the
optimum magnitude for subsequent processing.
When LEC is enabled, the last data tap of the echo canceller is treated
These modes, used less often, can also be enabled through the MCI:
• A freeze coefficient mode disables the coefficient updates.
• A special mode zeros all of the coefficients.
• An additional mode zeros the output of the FIR with no effect on the
• Individual EC coefficients can be read and written through the MCI.
The delay of the transmit-symbol input to the NEC can be specified through
These modes, used less often, can also be enabled through the MCI:
• A freeze coefficient mode disables the coefficient updates.
• A special mode zeros all of the coefficients.
• An additional mode zeros the output of the look-up table with no effect on
• The 64 14-bit, individual NEC coefficients can be read and written
Two other modes, used less often, can also be enabled through the MCI:
• A freeze coefficient mode disables the coefficient update.
• The DAGC gain coefficient can be read or written through the MCI.
coefficients.
the coefficients.
through the MCI.
Preliminary Information
Processing.
Conexant
Figure 2-3, Receiver Digital Signal
2.0 Functional Description
Figure 2-3, Receiver
2.2 Receive Section
2-9