SI4712-B30-GM Silicon Laboratories Inc, SI4712-B30-GM Datasheet - Page 22

• Manufacturer Part Number: SI4712-B30-GM
• Description: IC TX FM RADIO W/RPS 20UQFN
• Manufacturer: Silicon Laboratories Inc

Specifications of SI4712-B30-GM

• 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
• Operating Temperature: -20°C ~ 85°C
• Package / Case: 20-UQFN, 20-µQFN
• Operating Supply Voltage (typ): 3.3/5V
• Operating Supply Voltage (min): 2.7V
• Operating Supply Voltage (max): 5.5V
• Operating Temp Range: -20C to 85C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 20
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Power - Output: -
• Memory Size: -
• Data Rate - Maximum: -
• Lead Free Status / Rohs Status: Supplier Unconfirmed

Si4712/13-B30
5.3.1. Stereo Encoder
Figure 14
breakdown for the various components of a typical MPX
signal.
The total modulation level for the MPX signal shown in
Figure 14, assuming no correlation, is equal to the
arithmetic sum of each of the subchannel levels
resulting in 102.67 percent modulation or a peak
frequency deviation of 77.0025 kHz (an instantaneous
frequency deviation of 75 kHz corresponds to 100
percent modulation). Frequency deviation is related to
the amplitude of the MPX signal by a gain constant,
K
where Δf is the frequency deviation; K
voltage-to-frequency gain constant, and A
amplitude of the MPX message signal. For a fixed
K
the MPX message signal must be scaled to give the
appropriate total frequency deviation.
Figure 14 shows a conceptual block diagram of an MPX
encoder used to generate the MPX signal. L(t) and R(t)
denote the time domain waveforms from the left and
right audio channels, and RDS(t) denotes the time
domain waveform of the RDS/RBDS signal.
22
RDS(t)
VCO
VCO
L(t)
R(t)
, as given by the following equation:
, the amplitude of all the subchannel signals within
shows
Figure 14. MPX Encoder
38 kHz
57 kHz
an
Δf
=
MPX Encoder
example
K
Frequency
Frequency
Doubler
Tripler
VCO
A
m
19 kHz
modulation
C
C
C
C
2
0
1
0
VCO
m
is the
is the
level
Rev. 1.1
m(t)
The MPX message signal can be expressed as follows:
m(t) = C
where C
amplitudes of the audio signals (L(t) ± R(t)), the 19 kHz
pilot tone, and the RDS subcarrier respectively, to
generate the appropriate modulation level. To achieve
the
K
set to 0.1, and C
audio frequency deviation of 0.9 x 75 kHz = 67.5 kHz, a
peak
0.1 x 75 kHz = 7.5 kHz, and a peak RDS frequency
deviation of 0.0267 x 75 kHz = 2.0025 kHz for a total
peak frequency deviation of 77.0025 kHz.
In the Si4712/13, the peak audio, pilot, and RDS
frequency deviations can be programmed directly with
the
commands with an accuracy of 10 Hz. For the example
in
programmed with the value 6750, the Transmit Pilot
Deviation with 750, and the Transmit RDS Deviation
with 200, generating peak audio frequency deviations of
67.5 kHz, peak pilot deviations of 7.5 kHz, and peak
RDS deviations of 2.0 kHz for a total peak frequency
deviation of 77 kHz. The total peak transmit frequency
deviation of the Si4712/13 can range from 0 to 100 kHz
and is equal to the arithmetic sum of the Transmit
Audio, Pilot, and RDS deviations. Users must comply
with local regulations on radio frequency transmissions.
Each of the individual deviations (transmit audio, pilot,
and RDS) can be independently programmed; however,
the total peak frequency deviation cannot exceed
100 kHz.
The Si4712/13 provides an overmodulation indicator to
allow the user to dynamically set the maximum
deviation level. If the instantaneous frequency exceeds
the
TX_AUDIO_DEVIATION property, the SQINT interrupt
bit (and optional interrupt) will be set.
VCO
Figure 14,
Transmit
= 75 kHz/V, C
+ C
+ C
modulation
deviation
0
0
[L(t) + R(t)] + C
0
2
, C
[L(t) – R(t)] cos(2
RDS(t) cos(2
pilot
1
, and C
Audio,
2
the
would be set to 0.0267 giving a peak
0
would be set to 0.45; C
frequency
level
levels
Transmit
2
π
1
57 kHz)
are gains used to scale the
Pilot,
cos(2
π
38 kHz)
π
specified
of
19 kHz)
and
Audio
Figure 14
deviation
RDS
Deviation
1
by
Deviation
would be
with
the
of
is