BCM4330 Preliminary Data Sheet
Autotune and Search Algorithms
Autotune and Search Algorithms
The BCM4330 supports a number of FM search and tune functions that allows the host to implement many
convenient user functions, which are accessed through the Broadcom FM stack.
• Tune to Play—Allows the FM receiver to be programmed to a specific frequency.
• Search for RSSI > Threshold—Searches for valid FM channels within the band that have signal strength
above a specified threshold. This function can be set to search for the next valid channel up or down the
band or can be set to search for a list of valid channels across the entire band.
• Search for RSSI < Threshold—Searches for empty or under-utilized channels that can be used to transmit
FM. Available channels can be identified before suggesting an FM transmit channel to the user. This allows
the BCM4330 to determine the best channel for FM transmit operation instead of requiring the user to
find an unused channel manually.
• 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 requirements 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 information, 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.
Audio Features
A number of features are implemented in the BCM4330 to provide the best possible audio experience for the
user.
• Mono/Stereo Blend or Switch—The BCM4330 provides automatic control of the stereo or mono settings
based on the RSSI and estimated audio SNR. This feature is used to achieve a minimum audio SNR based
on the channel conditions. Two modes of operation are supported:
– Blend—In this mode, fine control of stereo separation is used to achieve optimal audio quality over a
wide range of input C/N. The amount of separation is fully programmable. In Figure 21, the separation
is programmed to maintain a minimum 50 dB SNR across the blend range.
– Switch—In this mode, the audio switches from full stereo to full mono at a predetermined level to
maintain optimal audio quality. The stereo-to-mono switch point and the mono-to-stereo switch points
are fully programmable to provide the desired amount of audio SNR. In Figure 22, the switch point is
programmed to switch to mono to maintain a 40 dB SNR.
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BROADCOM
BCM4330 Preliminary Data Sheet
April 28, 2011 • 4330-DS304-RI
Page 68
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