SI4713-B30-GMR Silicon Laboratories Inc, SI4713-B30-GMR Datasheet - Page 26

• Manufacturer Part Number: SI4713-B30-GMR
• Description: IC TX FM RADIO RPS/RDS 20UQFN
• Manufacturer: Silicon Laboratories Inc

Specifications of SI4713-B30-GMR

• Frequency: 76MHz ~ 108MHz
• Applications: General Purpose
• Modulation Or Protocol: FM
• Current - Transmitting: 18.8mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 2.7 V ~ 5.5 V
• Package / Case: 20-UQFN, 20-µQFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Power - Output: -
• Operating Temperature: -
• Memory Size: -
• Data Rate - Maximum: -

Si4712/13-B30
5.6. Audio Dynamic Range Control
The Si4712/13 includes digital audio dynamic range
control with programmable gain, threshold, attack rate,
and release rate. The total dynamic range reduction is
set by the gain value and the audio output compression
above
Threshold/(Gain + Threshold) in dB. The gain specified
cannot be larger than the absolute value of the
threshold. This feature can also be disabled if audio
compression is not desired.
The audio dynamic range control can be used to reduce
the dynamic range of the audio signal, which improves
the listening experience on the FM receiver. Audio
dynamic range reduction increases the transmit volume
by decreasing the peak amplitudes of audio signals and
increasing the root mean square content of the audio
signal. In other words, it amplifies signals below a
threshold by a fixed gain and compresses audio signals
above
Threshold/(Gain + Threshold).
example transfer function of an audio dynamic range
controller with the threshold set at –40 dBFS and a
Gain = 20 dB relative to an uncompressed transfer
function.
For input signals below the threshold of –40 dBFS, the
output signal is amplified or gained up by 20 dB relative
to an uncompressed signal. Audio inputs above the
threshold are compressed by a 2 to 1 dB ratio, meaning
that every 2 dB increase in audio input level above the
threshold results in an audio output increase of 1 dB. In
this example, the input dynamic range of 90 dB is
reduced to an output dynamic range of 70 dB.
26
Figure 18. Audio Dynamic Range Transfer
–90
–80
= 20 dB
a
Gain
the
–70
M = 1
M = 1
threshold
–60
threshold
Threshold
= –40 dB
–50
Function
Input [dBFS]
–40
Compression
by
–30
Compression
2:1 dB
Figure 18 shows
No
is
–20
the
–10
equal
ratio
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
Rev. 1.1
an
to
of
Figure 19 shows the time domain characteristics of the
audio dynamic range controller. The attack rate sets the
speed with which the audio dynamic range controller
responds to changes in the input level, and the release
rate sets the speed with which the audio dynamic range
controller returns to no compression once the audio
input level drops below the threshold.
5.7. Audio Limiter
The 4712/13 also includes a digital audio limiter. The
audio limiter prevents over-modulation of the FM
transmit output by dynamically attenuating peaks in the
audio input signal that exceed a programmable
threshold.
programmed audio deviation + ten percent. The
threshold ensures that the output signal audio deviation
does not exceed the programmed levels, avoiding
audible artifacts or distortion in the target FM receiver,
and complying with FCC or ETSI regulatory standards.
The limiter performs as a peak detector with an attack
rate set to one audio sample, resulting in an almost
immediate attenuation of the input peak. The recover
rate is programmable to the customer’s preference, and
is set by default to 5 ms. This is the recommended
setting to avoid audible pumping or popping. Refer to
“AN332: Universal Programming Guide.”
Figure 19. Time Domain Characteristics of the
Output
Audio
Audio
Input
Threshold
Audio Dynamic Range Controller
The
limiter
Attack
time
threshold
is
Release
set
time
to
the