U4065B Datasheet, PDF (7/23 Pages) TEMIC Semiconductors – FM Receiver

U4065B
The circuit blocks interference sensor and IF & detector
build up a second IF chain. In an FM system, the max
deviation of a 3rd order intermod signal is the triple max
deviation of the desired signal. Therefore the ceramic IF
BPF between Pin 11 and Pin 9 may be a large bandwidth
type. This external part is the only additional amount for
this unique feature.
A further narrow band AGC avoids overriding the second
IF amplifier. The amplitude information of the channel is
not compressed in order to maintain multipath detection
in the IF part of the receiver.
Level
Interfering signals
94 8820
Level
Interfering signals
94 8821
Intermod signal
Intermod signal
Desired
signal
Stereo-level
ÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇ Desired
frequency
Noise floor
Frequency
Desired
signal
Intermod signal
Stereo-level
Intermod signal
ÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇ Desired
frequency
Noise floor
Frequency
Figure 1 A high AGC threshold causes the intermod
signal to suppress the desired signal
Figure 2 The correct AGC threshold of the U4065B
provides optimum reception
Level
Strong signal
94 8822
Level
Strong signal
94 8823
Desired
signal
ÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇÇ _Desired
ÇÇÇÇÇÇÇÇÇÇÇÇ _frequency
Stereo-level
Noise floor
Frequency
Figure 3 A low AGC threshold causes the blocking
signal to suppress the desired signal
Desired
signal
Stereo-level
ÇÇÇÇÇÇÇÇÇÇÇÇ _Desired
ÇÇÇÇÇÇÇÇÇÇÇÇ _frequency
Noise floor
Frequency
Figure 4 The correct AGC threshold of the U4065B
provides optimum reception
Rev. A3, 15-Oct-98
7 (23)