PRELIMINARY
CYW43438
8.4.3 BBC Power Management
The following are low-power operations for the BBC:
■ Physical layer packet-handling turns the RF on and off dynamically within transmit/receive packets.
■ Bluetooth-specified low-power connection modes: sniff and hold. While in these modes, the CYW43438 runs on the low-power
oscillator and wakes up after a predefined time period.
■ Alow-powershutdownfeatureallowsthedevicetobeturnedoffwhilethehostandanyotherdevicesinthesystemremainoperational.
When the CYW43438 is not needed in the system, the RF and core supplies are shut down while the I/O remains powered. This
allows the CYW43438 to effectively be off while keeping the I/O pins powered, so they do not draw extra current from any other I/
O-connected devices.
During the low-power shut-down state, provided VDDIO remains applied to the CYW43438, 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 digital signals in the system and enables the CYW43438 to be fully integrated in an embedded device to take full
advantage of the lowest power-saving modes.
Two CYW43438 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
CYW43438 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.
8.4.4 FM Power Management
The CYW43438 FM subsystem can operate independently of, or in tandem with, the Bluetooth RF and BBC subsystems. The FM
subsystem power management scheme operates in conjunction with the Bluetooth RF and BBC subsystems. The FM block does not
have a low power state, it is either on or off.
8.4.5 Wideband Speech
The CYW43438 provides support for wideband speech (WBS) technology. The CYW43438 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.
8.4.6 Packet Loss Concealment
Packet Loss Concealment (PLC) improves the 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 bit-stream. 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 bit-stream and decode it as usual (frame repeat).
These techniques cause distortion and popping in the audio stream. The CYW43438 uses a proprietary waveform extension algorithm
to provide dramatic improvement in the audio quality. Figure 20 and Figure 21 show audio waveforms with and without Packet Loss
Concealment. Broadcom PLC/BEC algorithms also support wideband speech.
Figure 20. CVSD Decoder Output Waveform Without PLC
Packet losses causes ramp-down
Document Number: 002-14796 Rev. *K
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