bt8960 Mindspeed Technologies, bt8960 Datasheet - Page 33

• Manufacturer Part Number: bt8960
• Description: Bt8960, Single-chip 2b1q Transceiver
• Manufacturer: Mindspeed Technologies

Bt8960
Single-Chip 2B1Q Transceiver
2.2.4 Echo Canceler
2.2.5 Equalizer
2.2.4.2 Nonlinear Echo
Automatic Gain Control
2.2.4.1 Linear Echo
2.2.5.1 Digital
Canceler (NEC)
Canceler (LEC)
The EC removes images of the transmitted symbols from the received signal and
consists of two blocks: a linear and nonlinear echo canceler. The organization of
the blocks is displayed in Figure 2-3.
The Linear Echo Canceler (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 60-tap FIR filter with 32-bit linear adapted coeffi-
cients.
serves to cancel any DC offset that may be present.
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.
coefficients. It is also enabled through the microcomputer interface. Individual
EC coefficients can be read and written through the microcomputer interface.
Adaptation should be frozen prior to reading or writing coefficients.
The Nonlinear Echo Canceler (NEC) reduces the residual echo power in the echo
canceler output caused by nonlinear effects in the transmitter DAC, receiver
ADC, analog hybrid circuitry, or line cables.
microcomputer
[nonlinear_ec_modes; 0x09]. This allows the NEC to operate on the peak of the
echo regardless of differing delays in the echo path.
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.
effect on the coefficients. It is also 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.
Four LMS filters are used in the equalizer to process the echo canceler 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 feed-
back equalizer. Their interconnections are shown in Figure 2-3.
The 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 since
there is only one tap.
This mode disables the coefficient update only.
interface. Adaptation should be frozen prior to reading or writing the coefficient.
When enabled,
A freeze coefficient mode may be specified via the microcomputer interface.
An additional mode exists to zero the output of the FIR with no effect on the
The delay of the transmit-symbol input to the NEC can be specified via the
A freeze coefficient mode may be specified via the microcomputer interface.
An additional mode exists to zero the output of the look-up table with no
A freeze coefficient mode may be specified via the microcomputer interface.
The DAGC gain coefficient can be read or written through the microcomputer
interface:
the last data tap of the echo canceler is treated specially. This
N8960DSB
Nonlinear
Echo
Canceler
2.0 Functional Description
2.2 Receive Section
Mode
Register
23