參數(shù)資料
型號: CD6420
廠商: Cirrus Logic, Inc.
英文描述: FULL DUPLEX SPEAKERPHONE CHIP
中文描述: 的全雙工免提通話芯片
文件頁數(shù): 9/52頁
文件大小: 815K
代理商: CD6420
CS6420
DS205PP2
9
and they are post-compensated internally to pre-
vent any resultant passband droop. The ADCs also
expect a maximum of 1 V
rms
(2.8 V
pp
) at their in-
puts (which are biased around 2.12 VDC). A signal
of higher amplitude will clip the ADC input and
may result in poor echo canceller performance. See
the
Design Considerations
section for more details.
The outputs are delta-sigma digital to analog con-
verters (DACs) and have similar requirements to
the ADCs. The DACs are pre-compensated to ex-
pect a single-pole RC filter with a corner frequency
at 4 kHz. The full scale voltage output from a DAC
is 1 V
rms
(2.8 V
pp
) swinging around a DC bias of
2.12 V.
Acoustic Interface
The pins API (pin 20), APO (pin 18), MB (pin 19),
and AO (pin 3) make up the Acoustic Interface. A
block diagram of the Acoustic Interface is shown in
Figure 4.
API and APO are, respectively, the input and out-
put of the built-in analog pre-amplifier. The pre-
amplifier is an inverting amplifier with a fixed gain
of 34 dB biased around an input offset voltage
(V
off
) of 2.12 V. APO is the output of the pre-am-
plifier after a 1 k
resistor. The circuitry connected
to the amplifier input must present low source im-
pedance (<100
) to the API pin or the gain will be
reduced. When using the pre-amplifier, connecting
a 0.022
μ
F capacitor to ground off APO will pro-
vide the anti-aliasing filter required by the ADC, as
shown in Figure 2. The pre-amplifier may be by-
passed by clearing Mic (Register 0, bit 15) using the
Microcontroller Interface (see
Microcontroller In-
terface
section), grounding API through a capacitor,
and driving APO directly. In this case, the signal into
APO must be low-pass filtered by a single-pole RC
filter with a corner frequency at 8 kHz (see Figure 3).
Following the pre-amplifier is a programmable an-
alog gain stage (PGA) which is controllable
through the Microcontroller Interface. This gain
19 MB
18 APO
20
AO
3
0,6,9.5,12 dB
ADC
DAC
DAC
ADC
D
S
P
NI
17
NO
4
FAR-END
Transmit Path
Receive Path
API
3.5V
2.12V
1k
BANDGAP
34 dB
0,6,9.5,12 dB
NEAR-END
PGA
PGA
Figure 4. Analog Interface
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