Si4720-A10-GM Silicon Laboratories Inc, Si4720-A10-GM Datasheet - Page 31

• Manufacturer Part Number: Si4720-A10-GM
• Description: RF Transceiver Broadcast FM Radio Transceiver
• Manufacturer: Silicon Laboratories Inc

Specifications of Si4720-A10-GM

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

5.17. Line Input
The Si4720/21 provides left and right channel line inputs
(LIN and RIN). The inputs are high-impedance and low-
capacitance, suited to receiving line level signals from
external audio baseband processors. Both line inputs
are low-noise inputs with programmable attenuation.
Passive and active anti-aliasing filters are incorporated
to prevent high frequencies from aliasing into the audio
band and degrading performance.
To ensure optimal audio performance, the Si4720/21
has a TX_LINE_INPUT_LEVEL property that allows the
user to specify the peak amplitude of the analog input
(LILEVEL[9:0])
deviation level programmed in the audio deviation
property, TX_AUDIO_DEVIATION. A corresponding line
input attenuation code, LIATTEN[1:0], is also selected
by the expected peak amplitude level. Table 18 shows
the line attenuation codes.
(IMODE = 0110)
(IMODE = 1100)
(IMODE = 1000)
Left-Justified
(IFALL = 1)
(IFALL = 0)
LIATTEN[1:0]
(IFALL = 0)
00
01
10
11
Table 18. Line Attenuation Codes
(MSB at 2
(MSB at 1
INVERTED
DIN/DOUT
DCLK
DCLK
DFS
nd
st
rising edge)
rising edge)
DIN/DOUT
DIN/DOUT
required
DCLK
DFS
Voltage [mV]
Peak Input
MSB
1 DCLK
1
190
301
416
636
to
MSB
2
Figure 22. Left-Justified Digital Audio Format
1
reach
MSB
3
Figure 23. DSP Digital Audio Format
2
1
Resistance [kΩ]
RIN/LIN Input
the
LEFT CHANNEL
3
2
LEFT CHANNEL
396
100
74
60
maximum
n-2
3
LEFT CHANNEL
n-2
n-1
Rev. 1.0
n-1
n-2
LSB
n
The line attenuation code is chosen by picking the
lowest Peak Input Voltage in Table 18 that is just above
the expected peak input voltage coming from the audio
baseband processor. For example, if the expected peak
input voltage from the audio baseband processor is
400 mV, the user chooses LIATTEN[1:0] = 10 since the
Peak Input Voltage of 416 mV associated with
LIATTEN[1:0] = 10 is just greater than the expected
peak input voltage of 400 mV. The user also enters
400 mV into the LILEVEL[9:0] to associate this input
level to the maximum frequency deviation level
programmed into the audio deviation property. Note that
selecting a particular value of LIATTEN[1:0] changes
the input resistance of the LIN and RIN pins. This
feature is used for cases where the expected peak input
level exceeds the maximum input level of the LIN and
RIN pins.
The maximum analog input level is 636 mVpK. If the
analog input level from the audio baseband processor
exceeds this voltage, series resistors must be inserted
in front of the LIN and RIN pins to attenuate the voltage
such that it is within the allowable operating range. For
example, if the audio baseband's expected peak
amplitude is 900 mV and the V
the designer can use 30 kΩ series resistors in front of
the LIN and RIN pins and select LIATTEN[1:0] = 11. The
resulting expected peak input voltage at the LIN/RIN
pins is 600 mV, since this is just a voltage divider
between the LIN/RIN input resistance (see Table 18,
60 kΩ for this example) and the external resistor. Note
that the Peak Input Voltage corresponding to the chosen
LSB
n-1
n
MSB
LSB
1
n
MSB
1
MSB
2
1
2
3
2
RIGHT CHANNEL
3
Si4720/21-B20
3
RIGHT CHANNEL
RIGHT CHANNEL
n-2
IO
n-2
supply voltage is 1.8 V,
n-1
n-2
n-1
LSB
n-1
n
LSB
n
LSB
n
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