E12307

FM/AM Stereo Radio
CXA1838N
Description
The CXA1838N is the high performance one-chip bipolar IC designed for FM/AM stereo radios.
This IC includes an FM/AM front end, FM/AM IF amplifier, FM/AM detection output and FM stereo demodulator output.
Features
◆ Low current consumption（In FM mode ID=11.0 mA, in AM mode 8.5 mA, VCC=6.0 V）
◆ LED drive circuit for tuning
◆ LED drive circuit for stereo indicator
◆ Muting circuit for the FM band
◆ Few external parts
Package
30 pin SSOP（Plastic）
Structure
Bipolar silicon monolithic IC
Absolute Maximum Ratings
（Ta=25 ˚C）
Supply voltage
VCC
10
V
Operating temperature
Topr
-10 to +60
˚C
Storage temperature
Tstg
-55 to +150
˚C
Junction temperature
Tjmax
125
˚C
Allowable power dissipation
PD
500
mW
2 to 9
V
Recommended Operating Conditions
Supply voltage
VCC
1
CXA1838N
Block Diagram
PD
BU
FE
DET
IND
：PHASE DETECTOR
：BUFFER
：FRONT END
：DETECTOR
：INDICATOR
2
CXA1838N
Pin Description and Equivalent Circuit
Pin Voltage (V)
Pin
No.
1
Symbol
VCC=3 V
FM
AM
Equivalent circuit
VCC=6 V
FM
AM
PLL LPF1
29
PLL LPF2
2
PILOT
DET LPF1
MPX REG
26k
26k
0.86
0.86
0.86
0.86
LPF for PLL
29
0.95
0.95
0.95
Description
1
0.95
LPF capacitor (1 μF)
for PILOT DET inserted
between Pins 2 and 3.
3
2
3
PILOT
DET LPF2
4
ST IND/
VCO
CHECK
1.6
Rch OUT
0.66
0.95
0.95
0.95
0.95
MPX REG
5
1.6
4.5
VCO
0.66
1.5
Stereo Rch
output pin.
1.5
5
6
Lch OUT
7
VCC
6
0.66
0.66
1.5
1.5
Stereo Lch
output pin.
3
3
6
6
Supply pin.
17k
8
RIPPLE
FILTER
Stereo indicator drive
circuit and output for VCO
check.
4
13k
4.5
2.7
2.7
4
4
17k
8
130.4k
32.6k
3
Ripple filter.
CXA1838N
Pin Voltage (V)
Pin
No.
9
Symbol
AGC/AFC1
VCC=3 V
FM
AM
1.47
1.15
Equivalent circuit
VCC=6 V
FM
AM
1.47
1.15
Description
AFC pin in J band,
determines time constant
of AGC in AM (depending
on external capacitor.)
9
22k
50k
3.25k
10
AGC/AFC2
11
GND
1.15
1.47
1.15
1.47
0
0
0
0
25k
AFC pin in W band,
determines time constant
of AGC in AM (depending
on external capacitor.)
10
25
25
MUTE
0.05
0.01
0.05
GND of FM/AM IF,
and DET stage.
Time constant for
muting provided.
0.01
11
REG
12
TUNE IND
13
FM IF IN
1.6
1.6
4.5
28k
4.5
FM IF input pin.
15
15
14
BAND
SELECT
AM IF IN
1.25
0
1.25
330
17
FM/AM
FE OUT
FE GND
13
0
FM/AM band switching pin:
AM at GND
and FM at OPEN.
3k
0
0
0
1k
14
0
0.57
0.2
0.8
FM Block
0
0
AM/FM IF output pin to
connect to IF filter.
0.2
220
0
AM IF input pin.
2k
AM Block
16
AM/FM tuning indicator
drive circuit.
12
0
3p
16
GND for FM/AM front end.
20
18
FM RF IN
0.3
0
0.3
0
18
17
20
FM RF
1.25
1.25
1.25
1.25
4
1k
FM RF amplifier circuit for
FM RF input.
FM RF amplifier circuit to
connect to FM tank circuit.
CXA1838N
Pin Voltage (V)
Pin
No.
Symbol
VCC=3 V
FM
AM
Equivalent circuit
VCC=6 V
FM
AM
Description
FE REG
19
AM RF IN
1.25
1.25
1.25
1.25
AM RF input to connect to
bar antenna.
19
GND
21
REG
1.25
23
Regulator output
21
1.25
1.25
1.25
1.25V
REG
23
AFC
Variable capacitance for
AFC
22
REG
22
FM OSC
1.25
1.25
1.25
1.25
FM local oscillation circuit.
24
REG
24
AM OSC
1.25
1.25
1.25
1.25
AM local oscillation circuit.
26
1k
26
FM DISCRI
27
VCO
2.18
2.70
3.08
Phase shift circuit to
connect to ceramic
discriminator.
3.60
27
VCO control pin for stereo
demodulation.
28 MPX REG
28
MPX REG
30
GND
1.65
1.65
1.65
1.65
0
0
0
0
Regulator for MPX.
30
5
GND of MPX block.
SEP
A1
IS
GV1
Separation
FM MUTE
STEREO indicator output
FM front end voltage gain
6
△F1
IB1
VI1
VI2
GV2
GV3
VD3
THD2
IB2
FM meter current
MONO/STEREO switching
level by IF input
Auto blend
AM front end voltage gain
AM IF voltage gain
AM detection output level L,R
AM IF distortion L,R
AM meter current
THD1
VD2
FM IF center frequency deviation
FM IF distortion L,R(STEREO)
FM IF distortion L,R(MONO)
FM IF knee level
FM detection output level L,R（STEREO)
VD1
ID2
FM circuit current
FM detection outout level L,R（MONO)
ID1
AM circuit current
Item
VD
IB
VD
VIN4
VB
VIN3
IS
IB
VF
VD
Vin3
VD
VA
IS
VD
VD
ID
ID
Measure
Signal -ment
point
Electrical Characteristics　(Ta=25℃、 Vcc=6V)
↓
Vin2=95dBμ V 1660kHz (1kHz 30% MOD)
VD=1kHz sin wave, VCC=7.8V
↓
↓
Vin4=85dBμ V 455kHz (1kHz 30% MOD)
VD=1kHz sin wave
Vin4=85dBμ V 455KkHz CW
↓
↓
↓
↓
↓
↓
↓
↓
Vin4 level at output of 15.5mVrms
Vin2=60dBμ V 1660kHz CW,
VB=455kHz CW
STEREO → MONO switching level
MONO → STEREO switching level
Vin3=60dBμ V 10.7MHz CW
Vin3=90dBμ V 10.7MHz CW
Vin3=90dBμ V 10.7MHz, 1kHz 75kHz dev.
VD=1kHz sin wave
Input level decreased by 3dB compared to
the output when Vin3=90dBμ V 10.7MHz,
1kHz 22.5kHz dev.
↓
↓
Vin3=90dBμ V 10.7MHz, 1kHz 22.5kHz dev.
VD=1kHz sin wave
↓
A
ATT amount of noise level for
Vin3=no signal S8 ON/OFF
Vin1=40dBμ V 100MHz CW,
VA=10.7MHz CW
B
Separation when Vin3=50ｄBμ V 10.7MHz,
1kHz 22.5kHz dev. input
Vin3=60dBμ V 10.7MHz CW, pilot on
↓
A
1
V1 to V5 input shorted with FM no signal
V1 to V5 input shorted with AM no signal
Output waveform and measurement method
A
↓
A/B
↓
A
A/B
↓
↓
A
A/B
A
A/B
↓
↓
A
A/B
↓
A
2
A
↓
↓
B
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
A
3
↓
↓
↓
↓
B
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
A
B
4
↓
↓
↓
A
B
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
A
5
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
B
A
↓
↓
↓
↓
B
6
SW condition
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
OFF
OFF
/ON
↓
↓
OFF
8
↓
↓
↓
↓
A
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
B
↓
A
9
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
OFF
10
1.3
-
35.0
15
19
1
33
36
1.8
-50
-
-
35.0
28
1.8
16
30
7.0
5.0
Min.
3.0
0.6
77.5
21
24
10
41
43
3.5
0
0.1
25
77.5
35
3.0
23
40
11.0
8.5
Typ.
7.0
2.0
138
29
28
41
46
48
7.0
50
2.0
31
138
42
7.0
30
-
15.0
12.0
Max.
mA
%
mVrms
dBμ V
dB
dB
dBμ V
mA
kHz
%
dBμ V
mVrms
dB
mA
dB
dB
mA
mA
Unit
0dBμ V=1μ V
CXA1838N
Electrical Characteristics
CXA1838N
Electrical Characteristics Measurement Circuit
7
CXA1838N
Application Circuit
BPF
CF1
CF2
CF3
IFT
：FM BAND PASS FILTER
：AM 455 kHz CF
：FM 10.7 MHz CF
：FM DISCRIMINATOR
：AM 455 kHz IFT
Application circuits shown are typical examples illustrating the operation of the devices. Sony cannot
assume responsibility for any problems arising out of the use of these circuits or for any infringement of
third party patent and other right due to same.
8
CXA1838N
Example of Representative Characteristics
FM In pu t / Ou t pu t c h ar ac t e r ist ic s
0
VC C
3V
FREQ 9 8 M Hz
M ODE 4 0 0 Hz
DEV
2 2 . 5 kHz
SIGNAL(ST EREO)
Se par at io n / Re spo n se [dB]
-10
SIGNAL(M ONO)
-20
-30
NOISE
(ST EREO)
-40
-50
SEPARAT ION
NOISE(M ONO)
L → R
R → L
(W it h LPF)
-60
-70
0
10
20
30
40
50
60
70
80
90
100
110
In pu t sign al le ve l [dBμ V]
FM In pu t / Ou t pu t c h ar ac t e r ist ic s
5
VC C
3V
FREQ 9 8 M Hz
M ODE 4 0 0 Hz
DEV
2 2 . 5 kHz
Dist o r t io n THD1 [dB]
4
3
2
1
0
0
10
20
30
40
50
60
70
80
90
100
110
In pu t sign al le ve l [dBμ V]
46
79
44
Se par at io n [dB]
VC O fr e e - r u n n in g fr e qu e n c y [kHz]
Vin 3 = 9 0 dBu V 1 0 . 7 M Hz C W
78
77
76
42
40
Vin 3 = 9 0 dBu V 1 0 . 7 M Hz
38
75
fm o d= 1 kHz 2 2 . 5 kHz de v.
Pilo t ON
T h e e m par at u r e c h ar ac t e r ist ic s o f VC O
c o n t r o l r e sist an c e is be st at - 8 8 0 ppm / ℃.
74
-20
36
0
20
40
60
71
80
72
73
74
75
76
77
78
VC O fr e e - r u n n in g fr e qu e n c y [kHz]
Am bie n t t e m pe r at u r e T a [℃]
9
79
80
81
CXA1838N
AM In pu t / Ou t pu t c h ar ac t e r ist ic s
0
VC C
3V
FREQ 1 0 0 0 kHz
M OD 4 0 0 Hz 3 0 %
Sign al
-10
-30
-40
No ise
-50
-60
-70
10
20
30
40
50
60
70
80
90
100
110
In pu t sign al le ve l [dBμ V]
AM In pu t / Ou t pu t c h ar ac t e r ist ic s
5
VC C
3V
FREQ 1 0 0 0 kHz
M OD 4 0 0 Hz 3 0 %
4
Dist o r t io n THD2 [dB]
Re spo n se [dB]
-20
3
2
1
0
10
20
30
40
50
60
70
In pu t sign al le ve l [dBμ V]
10
80
90
100
110
CXA1838N
Coil Data
AM OSC
3
S
4
2
5
1
6
Core diameter φ0.06mm 2UEW
L (μH)
Qo
f (kHz)
1～3
1～3
FM RF
Number of windings(t)
1～3
4～6
796
270
125
107
29
Equivalent to L-5K7H5 R12-1684X Mitsumi Electric Co., Ltd.
or 7TRS-8441 TOKO Co., Ltd.
Φ5mm
Φ6mm 3.5t
AM IFT
3
S
4
2
5
1
6
Core diameter φ0.07mm UEW
FM OSC
Number of windings(t)
Co（pF）
Qo
1～3
1～3
1～2
2～3
4～6
180
90
111
35
7
Equivalent to 21K7H5 R12-8558A Mitsumi Electric Co., Ltd.
or 7MC-7789N TOKO Co., Ltd.
FM DISCRIMINATOR
3
4
2
5
1
6
Core diameter φ0.1mm 2UEW
Number of windings(t)
Co（pF）
Qo
1～3
1～3
1～2
82
95
111
Equivalent to 119ASC-12200Z TOKO Co., Ltd.
AM Bar Antenna
Primary
f（kHz） L（μH）
796
650
Primary
91t
Secondary
20t
Secondary
BPF
CF1
CF2
CF3
VC
VC（Rear Mount）
PFWE8
（88 to 108 MHz）
SFU-455B
SFE10.7MA5
CDA10.7MG1
PVC2LXT16L
HU22124N700
PVC2LXT16B
Soshin Electric Co., Ltd.
Murata Mfg. Co., Ltd. or BFCFL-455 TOKO Co. Ltd.
Murata Mfg. Co., Ltd.
Murata Mfg. Co., Ltd.
Mitsumi Electric Co., Ltd.
TOKO Co., Ltd.
Mitsumi Electric Co., Ltd.
11
Φ4mm
Φ0.6mm 3.5t
CXA1838N
Notes on Operation
1. VCO free-running frequency adjustment method
As this IC has the built-in oscillation capacitance, the oscillation frequency can be controlled with an
external resistor.
27
28
Thermistor 100
10k
Capacitor for decoupling
10μ
22k
1） VCO adjustment method
Pin 4 is the stereo indicator and VCO check pin. Therefore, in stereo mode (when stereo indicator drive
Tr Q2 is switched on), the Pin 4 voltage lowers down, Q1 is cut off and VCO Oscillation waveform can
not be seen. In AM mode as well, the oscillation waveform can not be seen as VCO turns off.
Adjust the free-running frequency to 76 kHz ±50 Hz. The capture range is about ±4 %.
33k
4
Q1
Vcc
Q2
About 180ｍVp-p
In this IC, the tuner and MPX blocks are directly connected. Therefore, the free-running frequency is
not stable, being affected by the noise except in reception mode. For free-running frequency adjustment,
input signals from RF or IF.
(The input signal should be RF [tuned frequency] or f0 of the discriminator using IF, and input more than
60 dBμV)
2） Control resistor of VCO oscillation frequency
For the VCO control resistor of this IC, a carbon film resistor is enough. For easier adjustment of temperature
characteristics and VCO free-running frequency, the following combination is recommended.
28
27
Thermistor 10010k
22k
10μ
3） How to deal with Pin 4 after adjustment
A. With the use of a stereo indicator.
2.2k
4
When VCC is 3 V or more, insert a bypass
resistor R to prevent LED malfunction.
Vcc=3V
2.2k
4
12
Vcc>3V
CXA1838N
B. Without the use of a stereo indicator
OPEN
4
4
2. MPX circuit
1) MPX load resistance
When the power supply voltage is over 3 V, change the MPX load resistors R6 and R7 from 3.3 kΩ to
6.8 kΩ. In this case, the output level is increased by about 6 dB.
2) Time constant of de-emphasis
Refer to the following table as the time constant is determined at C13 and C14.
R6,R7
3.3 kΩ
6.8 kΩ
50 μS
0.015 μS
0.0082 μS
75 μS
0.022 μS
0.012 μS
3. AFC circuit
1) This IC has a built-in variable capacitances.
Change to the following circuit when designing for J band, because the standard circuit is for W band.
3pF
23
22
9
10
1μ
150k
4.7μ
1μ
2) AFC pull-in range is expanded by increasing the capacitance 3 pF of standard circuit C7.
Adjust the value of capacitance according to the set specification.
4. Auto blend circuit
This IC has a built-in auto blend circuit and a monaural switch is not required as a rule. This circuit controls
the separation in proportion to the signal level and reduces the noise automatically for stereo reception below
the mid electric field when the electric field strength reaches lower than about 40 dBμV. When the electric
field strength becomes below 10 dBμV to 15 dBμV, monaural operation is automatically activated.
The switch monaural mode on externally, ground Pin 33 with 33 kΩ.
2
3
33k
MONO
SW
13
CXA1838N
5. FM discriminator
For FM detection, the quadrature detection system is adopted. As a phase shifter, a ceramic reasonator
(CF3 discriminator) is employed to achieve adjustment-free detection. Though the sensitivity and selectability
will be slightly affected, the discriminator can be replaced by a coil as shown below. Combining CF2(FM IF)
and CF3(FM discriminator) poses problems with the detection factor when deviation with the IF band center
frequency f0 occurs. To this effect, use pairs of the same rank as indicated in the chart.
F0 of CF2 and CF3
A Red
10.70 MHz
B Blue
10.67 MHz
C Orange
10.73 MHz
D Black
10.64 MHz
E White
10.76 MHz
26
22pF
DISCRIMINATOR
COIL
6. FM muting circuit
This IC has a built-in soft muting circuit.
As shown in the following Input/Output characteristics diagram, 23 dB (typ.) muting is applied and noise level
reduces for weak electric field and out of tune instances.
RESPONSE [dB]
Conventional IC
-3
-23
S+N
IC with built-in soft MUTE
N
INPUT LEVEL [dBμV]
7. Notes on patterns
1) Positions of FM Antenna and OSC coils
Locate those at right to each others to avoid inductance M through coupling. Further, insert a Pin 21
pattern between patterns of Pins 22,30 and coils.(See the reference circuit board).
2) Tuning circuit
As the capacitances C1 to C4, L2 and L3 are the constants on the standard circuit board, check the
constants when a new circuit board is used.
3) Ground pins
Pin 17 is a ground pin for AM, FM and FE; Pin 11 for IF; and Pin 30 for MPX. Use as thick a pattern as
possible since the grounding between ANT IN, BPF and Pin 11 significantly affects the stability, NF characteristics.
ANT
IN
BPF
18
17
16
4) Ground bypass capacitors C5 (0.001 μF) and C6 (10 μF) connected to Pin 21 as close to Pin 17 as possible.
14
CXA1838N
Package Outline
Unit : mm
15
CXA1838N
Marking
16
CXA1838N
Note
Sony reserves the right to change products and specifications without prior notice.
This information does not convey any license by any implication or otherwise under any patents or other right.
Application circuits shown, if any, are typical examples illustrating the operation of the devices. Sony cannot assume
responsibility for any problems arising out of the use of these circuits.
17