U4255BM-MFN Atmel, U4255BM-MFN Datasheet - Page 7

• Manufacturer Part Number: U4255BM-MFN
• Description: IC RCVR AM/FM FRONT-END 44-SSOP
• Manufacturer: Atmel

Specifications of U4255BM-MFN

• Frequency: 70MHz ~ 160MHz
• Modulation Or Protocol: AM, FM
• Applications: AM/FM Radio Receiver
• Current - Receiving: 50mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 7.5 V ~ 10 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Features: -
• Sensitivity: -
• Memory Size: -
• Data Rate - Maximum: -

2
IF-AGC
2
4519A–AUDR–03/02
nd
nd
IF Amplifier
IF Output
Table 8. 2
The LO frequency of the 2
is usually generated by the PLL circuit U4256BM.
In AM and WB mode, the input of the second IF amplifier is Pin 28, which is externally
connected to the 2
tivity. During normal FM operation (Bit 54 = 0), the input of the second IF amplifier is
connected to the 2
used for channel selectivity only. It is possible to use an additional external filter
between the 2
Table 9. 2
The IF-AGC controls the level of the 2
input or the integrated FM bandfilter and to the 2
Two different time constants of the IF-AGC can be selected by the capacitors at Pin 35
(IFAGCH) and Pin 36 (IFAGCL). The short time constant (IFAGCL) is used in FM mode
and in AM search mode. The long time constant (IFAGCH) is used for AM reception.
Table 10. IF-AGC Time Constant
In FM/WB mode, the output signal of the FM demodulator is applied to Pin 35 via a
series resistor of about 95 k . This low-pass filtered output signal of the FM demodula-
tor is used for the FM demodulator fine adjustment, for muting and as a reference for the
deviation sensor.
The 2
AM mode, this signal may be used for an external AM stereo decoder. Alternatively, a
signal corresponding to the logarithmic field strength after the integrated FM band filter,
which is used for multipath detection, can be switched to Pin 20 by setting Bit 55 = 1.
Bit 61
0
0
1
1
nd
AM reception
AM search
IF after the gain-controlled 2
FM/WB
Mode
nd
nd
Mixer Output Resistance in FM Mode
IF Filter in FM Mode
Bit 60
nd
0
1
0
1
mixer tank and Pin 28 in FM mode by setting Bit 54 to 1.
External and internal filter
nd
nd
mixer tank through the AM ceramic filter to achieve channel selec-
mixer output (Pin 23, Pin 24) and the integrated FM band filter is
2nd IF Filter
Internal filter
Output Resistance (Bit 54 = 0)
nd
Bit 92
mixer (10.25 MHz) has to be applied at Pin 22. This signal
1
0
0
0.63 k
0.47 k
0.29 k
3.3 k
nd
nd
IF amplifier is available at Pin20 (Bit 55 = 0). In
IF signal that is passed to the AM demodulator
Bit 88
X
0
1
nd
IF output Pin 20.
Output Resistance (Bit 54 = 1)
IF AGC Time Constant
IFAGCH (slow)
IFAGCL (fast)
IFAGCL (fast)
U4255BM-M
~ 100 k
0.78 k
0.55 k
0.32 k
Bit 54
0
1
7