U4254BM Datasheet, PDF (5/12 Pages) TEMIC Semiconductors – Low-Noise AM/FM Antenna Impedance Matching IC

U4254BM
Functional Description
The U4254BM is an integrated AM/FM antenna imped-
ance matching circuit. It compensates cable losses
between the antenna (for example windscreen, roof or
bumper antennas) and the car radio which is usually
placed far away from the antenna.
The FM amplifier provides excellent noise performance.
External components are used to adjust the gain and the
input-output matching impedance. Therefore it is
W ^{possible to adjust the amplifier to various cable}
impedances (usually 50, 75 or 150 ). To protect the
amplifier against input overload an Automatic Gain
Control (AGC) is included on the chip. The AGC
observes the AC voltage at the FM amplifier output,
rectifies this signal, and delivers DC current to dampen
the input antenna signal via an external PIN diode. The
threshold for the AGC is adjustable. Simple and
temperature compensated biasing is possible due to the
integrated voltage reference V_Ref2.
The AM part consists of a buffer amplifier. The voltage
gain of this stage is approximately one. The input
W resistance is 470 k , the input capacitance less than
W 10 pF. The output resistance is 125 . An excellent
dynamic range is achieved due to the complementary
CMOS source follower stage.
Absolute Maximum Ratings
Reference point is ground (Pins 2 and 7)
Parameters
Supply voltage
Power dissipation, P_tot at T_amb = 85°C
Junction temperature
Ambient temperature
Storage temperature
Electrostatic handling (HBM)
Thermal Resistance
Junction ambient
Parameters
Symbol
Value
Unit
V_S
8.8
V
P_tot
460
mW
T_j
150
°C
T_amb
–40 to +85
°C
"Tstg
V_ESD
–50 to +150
2000
°C
V
Symbol
R_thJA
Value
140
Unit
K/W
TELEFUNKEN Semiconductors
Rev. A1, 08-Jul-97
5 (12)