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During the low-power shut-down state, provided VDDIO remains applied to the CYW43353, all outputs are tristated, and most input
signals are disabled. Input voltages must remain within the limits defined for normal operation. This is done to prevent current paths
or create loading on any digital signals in the system and enables the CYW43353 to be fully integrated in an embedded device to
take full advantage of the lowest power-saving modes.
Two CYW43353 input signals are designed to be high-impedance inputs that do not load the driving signal even if the chip does not
have VDDIO power supplied to it: the frequency reference input (WRF_TCXO_IN) and the 32.768 kHz input (LPO). When the
CYW43353 is powered on from this state, it is the same as a normal power-up, and the device does not contain any information
about its state from the time before it was powered down.
5.5.4 Wideband Speech
The CYW43353 provides support for wideband speech (WBS) using on-chip SmartAudio technology. The CYW43353 can perform
subband-codec (SBC), as well as mSBC, encoding and decoding of linear 16 bits at 16 kHz (256 kbps rate) transferred over the
PCM bus.
5.5.5 Packet Loss Concealment
Packet Loss Concealment (PLC) improves apparent audio quality for systems with marginal link performance. Bluetooth messages
are sent in packets. When a packet is lost, it creates a gap in the received audio bitstream. Packet loss can be mitigated in several
ways:
Fill in zeros.
■
Ramp down the output audio signal toward zero (this is the method used in current Bluetooth headsets).
■
Repeat the last frame (or packet) of the received bitstream and decode it as usual (frame repeat).
■
These techniques cause distortion and popping in the audio stream. The CYW43353 uses a proprietary waveform extension algo-
rithm to provide dramatic improvement in the audio quality.
Loss Concealment. Cypress PLC and bit-error correction (BEC) algorithms also support wideband speech.
Document Number: 002-14949 Rev. *G
PRELIMINARY
Figure 6. CVSD Decoder Output Waveform Without PLC
Packet Loss Causes Ramp-down
Figure 6
and
Figure 7
show audio waveforms with and without Packet
CYW43353
Page 25 of 113
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