U4254BM Datasheet, PDF (4/12 Pages) TEMIC Semiconductors – Low-Noise AM/FM Antenna Impedance Matching IC

U4254BM
AMIN
The AM input has an internal bias voltage. The DC
W ^{voltage at this pin is VRef1/2. The input resistance is about}
470 k . The input capacitance is less than 10 pF.
VREF1/2
470 kW
8
VREF1
VREF1 is the stabilized voltage for the AM amplifier and
the AGC block. To achieve excellent noise performance
at LW frequencies, it is recommended that this pin is
m^{connected to ground via an external capacitor of about}
1 F.
VS
AMIN
ESD
12394
12
VREF1
Figure 8.
AMOUT, AMOUT1
GND1
ESD
12396
Figure 10.
The buffered AM amplifier consists of a complementary
pair of CMOS source followers. The transistor gates are
connected to AMIN. The pin AMOUT is the NMOS
transistor’s source, pin AMOUT1 is the PMOS transistor’
source. Due to the two different DC levels of these pins,
they have to be connected together via an external
capacitor of about 100 nF. By means of this technique an
excellent dynamic range can be achieved.
VREF2
For the DC biasing of the FM amplifier a second voltage
reference circuit is integrated. Because of temperature
independence of the collector current the output voltage
has a negative temperature coefficient of about –1 mV/K.
To stabilize this voltage an external capacitor to ground
of a few nF is recommended.
AMOUT1
ESD ¹¹
AMOUT
ESD ¹⁰
Figure 9.
13768
5
VREF2
ESD
GND1
12393
Figure 11.
GND2
GND2 is the ground for the AM amplifier.
4 (12)
TELEFUNKEN Semiconductors
Rev. A1, 01-Jul-97