U4254BM Datasheet, PDF (3/12 Pages) TEMIC Semiconductors – Low-Noise AM/FM Antenna Impedance Matching IC

U4254BM
Pin Description
FMIN
FMIN is the input of the FM amplifier. It is the base of a
bipolar transistor. A resistor or a coil is connected
between FMIN and VREF2. If a coil is used, noise perfor-
mance is excellent.
1
AGC
4
ESD
V_S
FMIN
ESD
12390
Figure 3.
GND1
To avoid crosstalk between AM and FM signals, the
circuit has two separate ground pins. GND1 is the ground
for the FM part.
FMGAIN
The DC current of the FM amplifier transistor is adjusted
by an external resistor which is connected between
FMGAIN and GND1. In order to influence the AC gain
of the amplifier, a resistor is connected in series to an
capacitor between FMGAIN and GND1. The capacitor
has to be a short at frequencies of 100 MHz.
12392
Figure 5.
AGCADJ
The threshold of the AGC can be adjusted by variing the
DC current at pin AGCADJ. If pin AGCADJ is connected
directly to GND1, the threshold is set to 96 dBµV at the
FM amplifier output. If a resistor is connected between
AGCADJ and GND1, the threshold is shifted to higher
values with increasing resistances. If AGCADJ is open,
the threshold is set to 106 dBµV.
65 kW
ESD
13
AGCADJ
12397
Figure 6.
FMGAIN
AGC
ESD
3
12391
Figure 4.
FMOUT
The FM amplifiers output is an open collector of a bipolar
RF-transistor. It should be connected to VS via a coil.
15
FMOUT
DC current flows into the AGC pin at high FM antenna
input signals. This current has to be amplified via the cur-
rent gain of an external PNP transistor that feeds a
PIN-diode. This diode dampens the antenna input signal
and protects the amplifier input against overload. The
maximum current which flows in the AGC pin is approxi-
mately 1 mA. In low end applications, the AGC function
is not necessary and therefore the external components
can be omitted.
ESD
12398
Figure 7.
TELEFUNKEN Semiconductors
Rev. A1, 08-Jul-97
3 (12)