w
A1—lnEL
A‘|_mEL®
Rev. 4772C–AUDR–08/04
Features
•High Dynamic Range for AM and FM
•Integrated AGC for FM
•High Intercept Point 3rd-order for FM
•FM Amplifier Adjustable to Various Cable Impedances
•High Intercept Point 2nd-order for AM
•Low-noise Output Voltage
•Low-power Consumption
Electrostatic sensitive device.
Observe precautions for handling.
Description
The U4254BM-M is an integrated low-noise AM/FM antenna impedance matching cir-
cuit in BiCMOS technology. The device is designed specifically for car applications
and is suitable for windshield and roof antennas.
Figure 1. Block Diagram
FM
AGC
FMIN
AGC
VS
AMIN
AMOUT
VREF1
FMOUT
FMGAIN
GND1
IAGC
AGCADJ
GND2
VREF2 VREF
1 (14)
2 (15)
4 (2)
3 (16)
5 (3)
7 (5)
8 (6)
10 (7)
14 (11)
12 (9)
13 (10)
15 (13)
AMOUT1
11 (8)
AM
() Pin numbers in brackets = QFN 4 × 4 package
Low-noise
AM/FM Antenna
Impedance
Matching IC
U4254BM-M
41m
33333333
CKCCKCCC
2U4254BM-M
4772C–AUDR–08/04
Pin Configuration
Figure 2. Pinning SO16 Figure 3. Pinning QFN16 4 × 4
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
FMGAIN
AGC
VREF2
NC
GND2
AMIN
FMIN
GND1
VS
AGCADJ
VREF1
AMOUT1
AMOUT
NC
NC
FMOUT
n.c.
AGC
VREF2
n.c.
n.c.
Vs
AGCADJ
VREF1
FMGAIN
FMGND
FMIN
FMOUT
GND2
AMIN
AMOUT
AMOUT1
16 15 14 13
5 6 7 8
1
2
3
4
12
11
10
9
Pin Description
Pin SSO16 Pin QFN16 Symbol Function
114FMINFM input
2 15 GND1 Ground for FM part
3 16 FMGAIN FM gain adjustment
4 2 AGC AGC output
5 3 VREF2 Reference voltage 2 output
6 1 NC Not connected
7 5 GND2 Ground for AM part
8 6 AMIN AM input
9 4 NC Not connected
10 7 AMOUT AM output
11 8 AMOUT1 AM output
12 9 VREF1 Reference voltage 1 output
13 10 AGCADJ Adjustment FM wide-band AGC threshold
14 11 VS Supply voltage
15 13 FMOUT FM output
16 12 NC Not connected
? ii
3
U4254BM-M
4772C–AUDR–08/04
Pin Description
FMIN FMIN, a bipolar transitor’s base is the input of the FM amplifier. A resistor or a coil is
connected between FMIN and VREF2. If a coil is used, the noise performance is
excellent.
Figure 4. Internal Circuit at Pin FMIN
GND1 To avoid cross-talk 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. To influence the AC gain of the amplifier, a
resistor is connected in series to a capacitor between FMGAIN and GND1. The capaci-
tor has to shorten frequencies of 100 MHz.
Figure 5. Internal Circuit at pin FMGAIN
AGC DC current flows into the AGC pin at high FM antenna input signals. This current has to
be amplified via the current gain of an external PNP transistor that feeds a PIN diode.
This diode dampens the antenna’s input signal and protects the amplifier input against
overload. The maximum current which flows in the AGC pin is approximately 1 mA. In
low-end applications, the AGC function is not necessary and the external components
can therefore be omitted.
ESD
1
FMIN
ESD
3
FMGAIN
4U4254BM-M
4772C–AUDR–08/04
Figure 6. Internal Circuit at Pin AGC
AGCADJ The threshold of the AGC can be adjusted by varying 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.
Figure 7. Internal Circuit at Pin AGCADJ
FMOUT The FM amplifier output is an open collector of a bipolar RF transistor. It should be con-
nected to VS via a coil.
Figure 8. Internal Circuit at Pin FMOUT
ESD
4
VS
AGC
ESD
13
65 kΩ
AGCADJ
ESD
15 FMOUT
5
U4254BM-M
4772C–AUDR–08/04
AMIN The AM input has an internal bias voltage. The DC voltage at this pin is VRef1/2. The input
resistance is about 470 kΩ. The input capacitance is less than 10 pF.
Figure 9. Internal Circuit at Pin AMIN
AMOUT, AMOUT1 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's 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.
Figure 10. Internal Circuit at Pins AMOUT1 and AMOUT
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 be con-
nected to ground via an external capacitor of about 1 µF.
ESD
8
470 kΩ
VREF1/2
AMIN
AMOUT1
ESD
ESD
AMOUT
11
10
_|
6U4254BM-M
4772C–AUDR–08/04
Figure 11. Internal Circuit at Pin VREF1
VREF2 For the DC biasing of the FM amplifier, a second voltage reference circuit is integrated.
Since the collector current is temperature independent, the output voltage has a nega-
tive temperature coefficient of about -1 mV/K. To stabilize this voltage, an external
capacitor to ground of a few nF is recommended.
Figure 12. Internal Circuit at Pin VREF2
GND2 GND2 is the ground for the AM amplifier.
ESD
12
VS
GND1
VREF1
ESD
5
GND1
VREF2
41m
7
U4254BM-M
4772C–AUDR–08/04
Functional Description
The U4254BM-M is an integrated AM/FM antenna impedance matching circuit. It com-
pensates cable losses between the antenna (for example windshield, 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 possible to
adjust the amplifier to various cable impedances (usually 50, 75 or 150 Ω). 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 VRef2.
The AM part consists of a buffer amplifier. The voltage gain of this stage is approxi-
mately one. The input resistance is 470 kΩ, the input capacitance less than 10 pF. The
output resistance is 125 Ω. An excellent dynamic range is achieved due to the comple-
mentary CMOS source follower stage.
Absolute Maximum Ratings
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating
only and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of this
specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Reference point is ground (pins 2 and 7)
Parameters Symbol Value Unit
Supply voltage VS8.8 V
Power dissipation, Ptot at Tamb = 85°CP
tot 460 mW
Junction temperature Tj150 °C
Ambient temperature Tamb -40 to +85 °C
Storage temperature Tstg -50 to +150 °C
Electrostatic handling (HBM at ESD S.5.1) ±VESD ±1000 V
Thermal Resistance
Parameters Symbol Value Unit
Junction ambient RthJA 140 K/W
41m
8U4254BM-M
4772C–AUDR–08/04
Electrical Characteristics
VS = 8 V, Tamb = 25°C, unless otherwise specified (see Figure 13 on page 9).
Parameters Test Conditions Pin Symbol Min. Typ. Max. Unit
Supply voltage 14 VS7.288.8V
Supply currents 14 IS3.5 4.8 5.6 mA
Reference voltage 1 output (I12 =0) 12 V
Ref1 5.1 5.4 5.7 V
Reference voltage 2 output (I5=0) 5 V
Ref2 2.3 2.6 2.8 V
Temperature dependence of VREF2 5 VRef2/∆T-1mV/K
AM Amplifier
Input resistance 8 RAMIN 470 kΩ
Input capacitance 8 CAMIN 10 pF
Output resistance 10 ROUT 125 Ω
Voltage gain 8, 10 a 0.85
Output noise voltage (rms value)
S1 switched to 2
B=6kHz
150 kHz to 300 kHz
500 kHz to 6.5 kHz
10 VN1
VN2
-2
-6
dBµV
dBµV
2nd harmonic
S2 switched to 1
fAMIN =500kHz
Output voltage =
110 dBµV
10 -65 dBc
FM Amplifier
Supply current limit IAGC, IAGCADJ =0A 15 I
15 33 35 mA
Input resistance f = 100 MHz 1 RFMIN 50 Ω
Output resistance f = 100 MHz 15 RFMOUT 50 Ω
Power gain f = 100 MHz 1, 15 G 5 dB
Output noise voltage f = 100 MHz
B = 120 kHz 15 VN0dBµV
3rd-order output intercept f = 100 MHz 15 132 dBµV
AGC
AGC input voltage threshold
f = 100 MHz
S2 switched to 1;
AGC threshold DC
current is 10 µA at
pin 4
15
Vth1 96 dBµV
AGC input voltage threshold
f = 100 MHz,
S2 switched to 2;
AGC threshold DC
current is 10 µA at
pin 4
15
Vth2 106 dBµV
AGC output current AGC active IAGC 1.2 mA
l—IF
__ LH—l
I
L‘JLJLIE
LJ E LJ
[I
I.
9
U4254BM-M
4772C–AUDR–08/04
Figure 13. Test Circuit
2
1
2.2
µF
S1
VS
150 Ω
2.2 nF
2.2 nF
51 Ω
22 Ω
2.2 nF
2.2 µH
AMOUT
2.2 µH
100 nF
2.2 nF
FMOUT
2.2 nF
1 nF
15 pF
AMIN
+
S2
12
18
9
16
5 kΩ
I4
FMIN
100 nF
VS
I3
I14
I15
LLLLL
flLLLL
10 U4254BM-M
4772C–AUDR–08/04
Figure 14. FM Intermodulation Distortion
90 95 100 105 MHz
Input
dBµV
103 dBµV
90 95 100 105 MHz
Output
dBµV
108 dBµV
58 dBµV
Gain = 5 dB
AGC not active
90 95 100 105 MHz
Input
dBµV 118 dBµV
90 95 100 105 MHz
dBµV
100 dBµV
50 dBµV
Output
AGC active
E
41m
11
U4254BM-M
4772C–AUDR–08/04
Figure 15. Test Circuit for AM Large Signal Behavior
Figure 16. AM Harmonic Distortion
DUT
1 nF
f = 500 kHz
V0
50 Ω
LPF
AMOUT
115 dBµV
Analyzer
fcutoff = 500 kHz 100 nF
5 kΩ
75 dBµV
AMIN Rin = 50 Ω
100 nF
AMOUT1
50 Ω
0.5 1.0 1.5
VAMOUT
(dBµV) 115 dBµV
50
70
110
90
55 dBµV
45 dBµV
f (MHz)
MgLT "
T
{EH
12 U4254BM-M
4772C–AUDR–08/04
Figure 17. Application Circuit
FM
AGC
AM
FMIN
AGC
AMIN
AMOUT1
VREF1
FMOUT
FMGAIN
FMGND
I
AGC
AGCADJ
AMGND
VREF2V
Ref
ANTENNA
AMFM
Protection
circuit
Output
VS
PIN
V
S
= 8.2 V
1 kΩ
BC55851
2.2 µH
R
1
2.2 nF
100 nF
200 nF
BA679
2.2 nF
39 pF
2.2 µH
2.2 nF
2.2 nF
510Ω
1 µF
+
2.2 nF
Vs
V
1 nF
R
2
100 nF
AMOUT
R
1
and R
2
depend on used FM cable impedance
FM cable impedanceR
1
(Ω)
50
75
100
125
150
150
270
390
470
620
22
33
51
86
160
R
2
(Ω)
A1—lnEL
13
U4254BM-M
4772C–AUDR–08/04
Package Information
Ordering Information
Extended Type Number Package Remarks
U4254BM-MFP SO16 –
U4254BM-MPG3 SO16 Taping corresponding, ICE-286-3
U4254BM-MPH QFN16 –
U4254BM-MPG3H QFN16 Taping corresponding, ICE-286-3
technical drawings
according to DIN
specifications
Package SO16
Dimensions in mm 10.0
9.85
8.89
0.4
1.27
1.4
0.25
0.10
5.2
4.8
3.7
3.8
6.15
5.85
0.2
16 9
18
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14 U4254BM-M
4772C–AUDR–08/04
.11_mEL®
Printed on recycled paper.
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4772C–AUDR–08/04
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