參數(shù)資料
型號(hào)： T4258NFN
廠商： ATMEL CORP
元件分類： 接收器
英文描述： AM/FM, AUDIO SINGLE CHIP RECEIVER, PDSO44
封裝： SSOP-44
文件頁(yè)數(shù)： 8/38頁(yè)
文件大?。?/td> 443K
代理商： T4258NFN
16
T4258N
4566B–AUDR–02/04
Field Strength Sensor
The field strength sensor provides a DC voltage at pin 9 which represents the logarith-
mic field strength of the signal in the reception band.
The field strength information can be retrieved either from a level detector at the input of
the 2nd mixer (pin 26) or from the IF-AGC depending on the setting of bit 80. The band-
width of the field strength detection in the AGC is smaller than by using the level
detector because of additional selectivity between the 2nd mixer and the 2nd IF amplifier
particularly in AM and WB, but the field strength detection in the AGC is limited to the IF
AGC range. Usually the field strength from the level detector is used in FM/WB mode
and the AGC field strength is used in AM mode.
The field strength output at pin 9 can be adjusted by the bits 18 to 21 in 0.5 dB steps.
This offset also has an influence on the soft mute levels.
Field Strength Selection
Bit 80 and bit 13 allows the switches between narrow-band field strength and wide-band
field strength information.
Search Stop Detector
A search stop detector is available in AM and FM/WB mode. A STOP condition is
signaled (with a low level at pin 21) if the frequency of the IF signal is within a window
around the center frequency of 450 kHz. The width of this search stop window can be
set by bit 85 to 87 in the range of 0.5 kHz to 80 kHz. The frequency of the IF signal is
measured by counting the number of periods of the IF signal during a measurement
time which is determined by bit 73 to 78. The inverted STOP signal is available at pin 21
according to Table 29 on page 17. The frequency of 10.25 MHz at pin 22 is used as a
time reference.
Table 25. Field Strength Offset
Offset Field Strength
Bit 21
Bit 20
Bit 19
Bit 18
0.0 dB
0
0.5 dB
0
1
1.0 dB
0
1
0
...
7.5 dB
1
Table 26. Field Strength (Combined)
Field Strength (Pin 9) Narrow-band/Wide-band
Bit 80
Bit 13
FM field strength (wide band)
0
Multipath field strength and FM field strength (wide band)
0
1
AM AGC field strength (narrow band)
1
0
Multipath field strength and AM AGC field strength (narrow band)
1
Table 27. Search Stop Detector Measurement Time
Time Window for Stop Signal
Bit 78
Bit 77
Bit 76
Bit 75
Bit 74
Bit 73
1
× 3.1969 ms
0
1
.....
63
× 3.1969 ms
1
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