CS6422-CS Cirrus Logic Inc, CS6422-CS Datasheet - Page 35

• Manufacturer Part Number: CS6422-CS
• Description: IC CODEC SPKRPHONE 2CH 20-SOIC
• Manufacturer: Cirrus Logic Inc
• Type: Audio Processorr

Specifications of CS6422-CS

• Mounting Type: Surface Mount
• Package / Case: 20-SOIC
• Applications: Speakerphones
• Peak Reflow Compatible (260 C): No
• Termination Type: SMD
• Supply Voltage Max: 5.5V
• Leaded Process Compatible: No
• Supply Voltage Min: 4.5V
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: 598-1199-5

14), and the receive suppression speech detector
threshold is set by RSThd (Register 2, bits 13 and
12). The transmit speech detectors for both half-du-
plex and suppression default to 6 dB.
Note that constant power signals which persist for
long durations, such as tones or white noise from a
signal generator, will be detected as speech only as
long as the background noise level has not risen to
within the speech detection threshold of the signal
power. When a tone has persisted for long enough,
the background noise level will be equal to the
power estimator level, and so the tone will no long-
er be considered speech. This duration is dependent
upon the power difference between the signal and
the ambient noise power, as well as NseRmp. It
should be noted that the CS6422 has a tone detector
to prevent updates when tones are present and allow
tones to persist regardless of the speech detectors.
4.1.2
In cases where the system relies on the echo cancel-
ler for stability, a fail-safe mechanism must be in
place for instances when the echo canceller is not
performing adequately. The CS6422 implements a
half-duplex mode to guarantee communication
even when the echo canceller is disabled.
When the CS6422 is first powered on, or emerges
from a reset, the echo canceller coefficients are
cleared, and the echo cancellers provide no benefit
at this point. The half-duplex mode is on to prevent
howling and echo from interfering with communi-
cation. Once the CS6422’s adaptive filters have
adapted sufficiently, the half-duplex mode is auto-
matically disabled, and full-duplex communication
can occur.
The half-duplex mode allows three states: <Trans-
mit>, <Receive>, and <Idle>. In the <Transmit>
state, the transmit channel is open and the receive
channel is muted. The <Receive> state mutes the
transmit channel. The <Idle> state is an internal
state which is used to enhance switching decision
DS295F1
Half-Duplex Mode
making. The CS6422 must be <Idle> before it will
allow a state change between <Transmit> and <Re-
ceive>.
The half-duplex controller can be susceptible to
echo, so a holdover timer is provided to help pre-
vent false switching. Holdover will force the chan-
nel to remain in its current state for a fixed duration
after speech has stopped. HDly (Register 2, bits 9
and 8) sets the duration of the holdover. Longer
holdover will tend to make interrupting more diffi-
cult, but will be more robust to spurious switching
caused by echo.
4.1.2.1
When enabled, this feature causes the CS6422 to
return to <Transmit> mode from an <Idle> state
when operating in half-duplex. This simulates
full-duplex-like behavior during the periods of
half-duplex operation at the beginning of a call.
4.1.3
The CS6422 implements a peak-limiting AGC in
both the transmit and receive directions in order to
boost low-level signals without compromising per-
formance when high amplitude signals are present.
The technique effectively results in dynamic range
compression.
The AGC works by setting a reference level based
on the value represented by TVol (Register 1, bits
11-8) for the transmit direction and RVol (Register
0, bits 11-8) for the receive direction. If the signal
from the input is above this reference, it is attenu-
ated to the reference level with an attack time of
125 µs. This attenuation level decays with a time
constant of 30 ms unless another signal greater than
the reference level is detected. After the attenua-
tion, a post-scaler scales the reference level to full-
scale (the maximum digital code), which amplifies
all signals by the difference between the reference
level and full-scale.
For example, Figure 11 shows how the AGC works
with a reference level of +30 dB (Word = 0000).
AGC
Idle Return to Transmit
CS6422
CS6422
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