PRELIMINARY
CYW43438
11. FM Receiver Subsystem
11.1 FM Radio
The CYW43438 includes a completely integrated FM radio receiver with RDS/RBDS covering all FM bands from 65 MHz to 108 MHz.
The receiver is controlled through commands on the HCI. FM received audio is available as a stereo analog output or in digital form
through PCM. The FM radio operates from the external clock reference.
11.2 Digital FM Audio Interfaces
The FM audio can be transmitted via the PCM pins, and the sampling rate is programmable. The CYW43438 supports a three-wire
PCM interface in either a master or slave configuration. The master or slave configuration is selected using vendor specific commands
over the HCI interface. In addition, multiple sampling rates are supported, derived from either the FM or Bluetooth clocks. In master
mode, the clock rate is either of the following:
■ 48 kHz x 32 bits per frame = 1.536 MHz
■ 48 kHz x 50 bits per frame = 2.400 MHz
In slave mode, clock rates up to 3.072 MHz are supported.
11.3 Analog FM Audio Interfaces
The demodulated FM audio signal is available as line-level analog stereo output, generated by twin internal high SNR audio DACs.
11.4 FM Over Bluetooth
The CYW43438 can output received FM audio onto Bluetooth using one of following three links: eSCO, WBS, or A2DP. For all link
types, after a link has been established, the host processor can enter sleep mode while the CYW43438 streams FM audio to the
remote Bluetooth device, thus minimizing system current consumption.
11.5 eSCO
In this use case, the stereo FM audio is downsampled to 8 kHz and a mono or stereo stream is sent through the Bluetooth eSCO link
to a remote Bluetooth device, typically a headset. Two Bluetooth voice connections must be used to transport stereo.
11.6 Wideband Speech Link
In this case, the stereo FM audio is downsampled to 16 kHz and a mono or stereo stream is sent through the Bluetooth wideband
speech link to a remote Bluetooth device, typically a headset. Two Bluetooth voice connections must be used to transport stereo.
11.7 A2DP
In this case, the stereo FM audio is encoded by the on-chip SBC encoder and transported as an A2DP link to a remote Bluetooth
device. Sampling rates of 48 kHz, 44.1 kHz, and 32 kHz joint stereo are supported. An A2DP lite stack is implemented in the
CYW43438 to support this use case, which eliminates the need to route the SBC-encoded audio back to the host to create the A2DP
packets.
11.8 Autotune and Search Algorithms
The CYW43438 supports a number of FM search and tune functions, allowing the host to implement many convenient user functions
by accessing the Broadcom FM stack.
■ Tune to Play—Allows the FM receiver to be programmed to a specific frequency.
■ Search for SNR > Threshold—Checks the power level of the available channel and the estimated SNR of the channel to help
achieve precise control of the expected sound quality for the selected FM channel. Specifically, the host can adjust its SNR require-
ments to retrieve a signal with a specific sound quality, or adjust this to return the weakest channels.
■ Alternate Frequency Jump—Allows the FM receiver to automatically jump to an alternate FM channel that carries the same infor-
mation, but has a better SNR. For example, when traveling, a user may pass through a region where a number of channels carry
the same station. When the user passes from one area to the next, the FM receiver can automatically switch to another channel
with a stronger signal to spare the user from having to manually change the channel to continue listening to the same station.
Document Number: 002-14796 Rev. *K
Page 48 of 101
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