ucb1100 NXP Semiconductors, ucb1100 Datasheet - Page 12

• Manufacturer Part Number: ucb1100
• Description: Advanced Modem/audio Analog Front-end
• Manufacturer: NXP Semiconductors

Philips Semiconductors
6.2 Telecom codec
The telecom codec contains an input channel, built up from a 64
times oversampling sigma delta analogue to digital converter (ADC)
with digital decimation filters, programmable attenuation and build in
sidetone suppression circuit. The output path consist of a digital up
sample filter, a 64 time oversampling 4 bit digital to analogue
converter (DAC) circuit followed by a differential output driver,
capable of directly driving a 600ohm isolation transformer. The
output path includes a mute function. The telecom codec also
incorporates a loopback mode, in which codec output path and the
input path are connected in series.
The telecom sample rate is derived from the SIB interface clock pin
(sibclk) and is programmable through the SIB interface. The telecom
sample rate is given by the following formula:
For example, a sibclk of 10 MHz, with a divisor of 40, results in a
telecom sample rate of 7.813kHz. Both the rising and the falling
1998 May 08
Advanced modem/audio analog front-end
Fst
toutp
toutn
(64 * telecom_divisor )
tinp
tinn
(2 * Fsibclk )
side tone suppression
echo on
low pass
Sinc4
FIR
FIR
(5
16
2
telecom_divisor
mute
half band
removal
loop inputs
loop inputs
loopback
DC
FIR
Figure 9. Detailed Block Diagram Telecom codec
mux
2
half band
WDF
attenuation
128)
round
up
2
effect
4 bit DAC
1 bit ADC
effect
half band
half band
12
WDF
FIR
edges of the sibclk are used in case an odd telecom_divisor is set.
In that case a 50% duty cycle of the sibclk signal is mandatory to
obtain time equidistant sampling.
The input path of the telecom codec has a programmable
attenuation. It also implements a voice band filter, which consists of
an digital low pass filter, which is a part of the decimation filter.
Therefore the pass band of the voice band filter is determined by the
selected telecom codec sample rate. This voice band filter is
activated by the high pass enable bit in the telecom control register
B. The resulting telecom input filter curves are given in Figures 11
and 12.
The output section of the telecom codec is designed to interface with
a 600 ohm line through an isolation transformer. The built in mute
function is activated by the mute bit in the telecom control register B.
The output driver remains active in the mute mode, however no
output signal is produced.
64fs
2
64fs
4
4
+3dB
shaper
noise
+3dB
2
telecom input enable
telecom output enable
4
half band
interpolator
FIR
high pass
FIR
2
removal
DC
round
Preliminary specification
up
14
UCB1100
fs
SN00134
14
fs