Single-chip Tuner IC for Car Radios

Ordering number : ENN6655
LA1787M
Monolithic Linear IC
Single-Chip Tuner IC
for Car Radios
http://onsemi.com
Overview
The LA1787M integrates all six blocks required in a car radio tuner on a single chip.
Functions
• FM front end
• AM up-conversion
• FM IF
• FM/AM switch
• Noise canceller
• MRC
• Multiple
Features
• Improved noise reduction methods
— The FM front end provides excellent 3-signal characteristics equivalent to those of the LA1193M.
— Superlative listenability due to improved medium and weak field noise canceller characteristics.
— Improved separation characteristics
— Anti-birdie filter
— Improved AM and FM thermal characteristics
— Excellent FM signal meter linearity
— Modified N.C. circuit for improved noise rejection
• Improved AM adjacent channel interference characteristics (40 kHz)
• Double conversion AM tuner (up conversion) Reduces the number of external components required as compared to
earlier double conversion tuners, in particular, no crystal is required (when used in conjunction with the LC72144).
• Sample-to-sample variation reduction circuit built into the FM IF circuit.
(Fixed resistors are used for the SD, keyed AGC, mute on adjustment, ATT, SNC, and HCC functions.)
• Improved FM separation temperature characteristics
• The LA1787 inherits the block arrangement of the LA1780M and supports pin-compatible designs.
Package Dimensions
unit : mm (typ)
0.8
1.0
17.2
14.0
0.35
1.6
1.0
0.15
1.6
1.0
33
48
32
0.8
17.2
14.0
49
1
16
15.6
3.0max
1.0
17
64
0.8
Semiconductor Components Industries, LLC, 2011
January, 2011
0.1
2.7
Allowable power dissipation,
Pd max mW
QIP64E(14X14)
Mounted on a 40 x 80 x 1.3 mm
glass epoxy printed circuit board
Independent IC
Ambient temperature, Ta
C
72602RM (OT) No. 6655-1/54
LA1787M
Specifications
Maximum Ratings at Ta = 25°C
Parameter
Symbol
Maximum supply voltage
Allowable power dissipation
Conditions
VCC1 max
Pins 6, 40, and 61
VCC2 max
Pins 7, 45, 54, 59, and 60
Pd max
Ratings
Unit
9
Ta ≤ 55°C
V
12
V
950
mW
Operating temperature
Topr
–40 to +85
°C
Storage temperature
Tstg
–40 to +150
°C
Operating Conditions at Ta = 25°C
Parameter
Symbol
VCC
Recommended supply voltage
VCCST IND
Operating supply voltage range
Conditions
Ratings
Unit
Pins 6, 7, 40, 45, 54, 59, 60, and 61
8
V
Pin 26
5
V
7.5 to 9.0
V
VCC op
Operating Characteristics at Ta = 25°C, VCC= 8.0V, in the specified test cricuit for the FM IF input
Ratings
Parameter
Symbol
Conditions
min
typ
max
unit
[FM Characteristics] At the FM IF input
Current drain
Demodulation output
Pin 31 demodulation output
Channel balance
Total harmonic distortion
ICCO-FM
VO-FM
VO-FM31
CB
No input, I40 + I45 + I54 + I59 + I60 + I61
60
94
110
mA
10.7 MHz, 100dBµ, 1 kHz, 100%mod, The pin 15 output
205
310
415
mVrms
10.7 MHz, 100dBµ, 1 kHz, 100%mod, The pin 31 output
190
295
380
mVrms
The ratio between pins 15 and 16 at 10.7 MHz, 100 dBµ, 1 kHz
–1
0
+1
dB
0.3
1
THD-FM mono
10.7 MHz, 100 dBµ, 1 kHz, 100% mod, pin 15
Signal-to-noise ratio: IF
S/N-FM IF
10.7 MHz, 100 dBµ, 1 kHz, 100% mod, pin 15
75
82
dB
AM suppression ratio: IF
AMR IF
10.7 MHz, 100 dBµ, 1 kHz, fm = 1 kHz, 30% AM, pin 15
55
68
dB
Att-1
10.7 MHz, 100 dBµ, 1 kHz. The pin 15
attenuation when V33 goes from 0 to 2 V
5
10
15
dB
Att-2
10.7 MHz, 100 dBµ, 1 kHz. The pin 15
attenuation when V33 goes from 0 to 2 V*1
15
20
25
dB
Att-3
10.7 MHz, 100 dBµ, 1 kHz. The pin 15
attenuation when V33 goes from 0 to 2 V*2
28
33
38
dB
10.7 MHz, 100 dBµ, L+R = 90%, pilot = 10%. The pin 15 output
ratio
30
40
Muting attenuation
Separation
Separation
Stereo on level
ST-ON
The pilot modulation such that V26 < 0.5 V
1.2
2.4
Stereo off level
ST-OFF
The pilot modulation such that V26 > 3.5 V
0.6
1.6
Main total harmonic distortion
THD-Main L
10.7 MHz, 100 dBµ, L+R = 90%, pilot = 10%. The pin 15 signal
Pilot cancellation
PCAN
10.7 MHz, 100 dBµ, pilot = 10%.
The pin 15 signal/the pilot level leakage. DIN audio
SNC output attenuation
AttSNC
10.7 MHz, 100 dBµ, L-R = 90%, pilot = 10%.
V28 = 3 V → 0.6 V, pin 15
%
dB
4.4
%
%
0.3
1.2
%
20
30
dB
1
5
9
dB
0.5
4.5
8.5
dB
AttHCC-1
10.7 MHz, 100 dBµ, 10 kHz, L+R = 90%, pilot = 10%.
V29 = 3 V → 0.6 V, pin 15
AttHCC-2
10.7 MHz, 100 dBµ, 10 kHz, L+R = 90%,
pilot = 10%. V29 = 3 V → 0.1 V, pin 15
6
10
14
dB
100 dBµ, 10.7 MHz, 30% modulation. The IF input such
that the input reference output goes down by 3 dB
33
40
47
dBµ
The IF input level (unmodulated) when V33 = 2 V
27
35
43
dBµ
The IF input level (unmodulated) (over 100 mV rms)
such that the IF counter buffer output goes on
54
62
70
dBµ
54
62
70
dBµ
VIFBUFF-FM
10.7 MHz, 100 dBµ, unmodulated. The pin 23 output
130
200
270
mVrms
VSM FM-1
No input. The pin 24 DC output, unmodulated
0.0
0.1
0.3
V
VSM FM-2
50 dBµ. The pin 24 DC output, unmodulated
0.4
1.0
1.5
V
VSM FM-3
70 dBµ. The pin 24 DC output, unmodulated
2.0
2.7
3.5
V
VSM FM-4
100 dBµ. The pin 24 DC output, unmodulated
4.7
5.5
6.2
V
Muting bandwidth
BW-mute
100 dBµ. The bandwidth when V33 = 2 V, unmodulated
150
220
290
kHz
Mute drive output
VMUTE-100
100 dBµ, 0 dBµ. The pin 33 DC output, unmodulated
0.00
0.03
0.20
V
HCC output attenuation
Input limiting voltage
Muting sensitivity
SD sensitivity
Vi-lim
Vi-mute
SD-sen1 FM
SD-sen2 FM
IF counter buffer output
Signal meter output
Continued on next page.
No. 6655-2/54
LA1787M
Continued from preceding page.
Ratings
Parameter
Symbol
Conditions
min
typ
max
unit
[FM FE Mixer Input
N-AGC on input
VN-AGC
83 MHz, unmodulated.
The input such that the pin 2 voltage is 2.0 V or below
81
88
95
dBµ
W-AGC on input
VWAGC
83 MHz, unmodulated. The input such that the pin 2
voltage is 2.0 V or below. (When the keyed AGC is set to 4.0 V.)
104
110
116
dBµ
83 MHz, 80 dBµ, unmodulated. The FE CF output
19
30
48
mVrms
No input
85
110
165
mVrms
Conversion gain
Oscillator buffer output
A.V
VOSCBUFFFM
[NC Block] NC input (pin 30)
Gate time
τGATE1
Noise sensitivity
NC effect
SN
SN-NC
f = 1 kHz, for a 1-µs, 100-mV p-o pulse
55
µs
The level of a 1 = kHz, 1-µs pulse input that starts
noise canceller operation. Measured at pin 30.
40
mVp-o
The pulse rejection effect provided by the noise canceller.
For a repeated 1-µs wide pulse, frequency = 10 kHz,
150 mV p-o. The ratio of the FM mode pin 15 output
referenced to the AM mode pin 15 output (effective value)
5
[Multipath Rejection Circuit] MRC input (pin 27)
MRC output
MRC operating level
VMRC
MRC-ON
V24 = 5 V
2.2
2.3
2.4
V
The pin 32 input level at f = 70 kHz such that
pin 24 goes to 5 V and pin 27 goes to 2 V
10
15
20
mVrms
[AM Characteristics] AM ANT input
Practical sensitivity
S/N-30
1 MHz, 30 dBµ, fm = 1 kHz, 30% modulation, pin 15
20
Detector output
VO-AM
1 MHz, 74 dBµ, fm = 1 kHz, 30% modulation, pin 15
130
195
270
mVrms
VO-AM31
1 MHz, 74 dBµ, fm = 1 kHz, 30% modulation, pin 31
110
175
230
mVms
VAGC-FOM
1 MHz, 74 dBµ, referenced to the output, the input amplitude
such that the output falls by 10 dB. Pin 15
51
56
61
dB
47
Pin 31 detector output
AGC F.O.M.
Signal-to-noise ratio
S/N-AM
1 MHz, 74 dBµ, fm = 1 kHz, 30% modulation
Total harmonic distortion
THD-AM
1 MHz, 74 dBµ, fm = 1 kHz, 80% modulation
Signal meter output
Oscillator buffer output
Wide band AGC sensitivity
SD sensitivity
IF buffer output
dB
52
dB
0.3
1
%
V
VSM AM-1
No input
0.0
0.2
0.5
VSM AM-2
1 MHz, 130 dBµ, unmodulated
4.8
6
7.3
No input, the pin 15 output
185
230
VOSCBUFF AM1
V
mVrms
W-AGCsen1
1.4 MHz, the input when V46 = 0.7 V
92
98
104
dBµ
W-AGCsen2
1.4 MHz, the input when V46 = 0.7 V (seek mode)
83
89
95
dBµ
SD-sen1 AM
1 MHz, the ANT input level such that the IF counter output turns on.
24
30
36
dBµ
SD-sen2 AM
1 MHz, the ANT input level such that the SD pin goes to the on state.
24
30
36
1 MHz, 74 dBµ, unmodulated. The pin 23 output
200
290
VIFBUFF-AM
dBµ
mVrms
Note: These measurements must be made using the either the IC-51-0644-824 or KS8277 IC socket (manufactured by Yamaichi Electronics).
* 1. When the resistor between pin 58 and ground is 200 kΩ.
* 2. When the resistor between pin 58 and ground is 30 kΩ.
No. 6655-3/54
LA1787M
Function List
FM Front End (Equivalent to the Sanyo LA1193)
• Double input type double balanced mixer
• Pin diode drive AGC output
• MOSFET second gate drive AGC output
• Keyed AGC adjustment pin
• Differential IF amplifier
• Wide band AGC sensitivity setting pin, and narrow
band AGC sensitivity setting pin
• Local oscillator
FM IF
• IF limiter amplifier
• S-meter output (also used for AM) 6-stage pickup
• Multipath detection pin (shared FM signal meter)
• Quadrature detection
• AF preamplifier
• AGC output
• Band muting
• Weak input muting
• Soft muting adjustment pin
• Muting attenuation adjustment pin
• IF counter buffer output (also used for AM)
• SD (IF counter buffer on level) adjustment pin
• SD output (active high) (also used for AM)
Noise Canceller
• High-pass filter (first order)
• Delay circuit based low-pass filter (fourth order)
• Noise AGC
• Pilot signal compensation circuit
• Noise sensitivity setting pin
• Function for disabling the noise canceller in AM
mode
Multiplex Functions
• Adjustment-free VCO circuit
• Level follower type pilot canceller circuit
• HCC (high cut control)
• Automatic stereo/mono switching
• VCO oscillation stop function (AM mode)
• Forced monaural
• SNC (stereo noise controller)
• Stereo display pin
• Anti-birdie filter
AM
• Double balanced mixer (1st, 2nd)
• IF amplifier
• Detection
• RF AGC (narrow/wide)
• Pin diode drive pin
• IF AGC
• Signal meter output (also used for FM)
• Local oscillator circuits (first and second)
• Local oscillator buffer output
• IF counter buffer output (also used by the FM IF)
• SD (IF counter buffer on level) adjustment pin
• SD output (active high) (also used for AM)
• Wide AGC
• Detection output frequency characteristics
adjustment pin (low cut, high deemphasis)
• AM stereo buffer
MRC (multipath noise rejection circuit)
AM/FM switching output (linked to the FM VCC)
No. 6655-4/54
LA1787M
Operating Characteristics and Symbols Used in the Test Circuit Diagrams
Switches (SW)
Switch on = 1, SW off = 0
There are two switches that use signal transfer.
— SW2: switches between the mixer input and the IF input.
— SW4: switches between noise canceler input and IF output + noise canceler input.
Types of SG used
PG1 (AC1)
Used for noise canceler testing. A pulse generator and an AF oscillator are required.
AC2
Used for FM front end testing. Outputs an 83 MHz signal.
AC3
Used for FM IF, noise canceler, and MPX testing. Outputs a 10.7 MHz signal. Stereo modulation must be possible.
AC4
Used for AM testing. Outputs 1 MHz and 1.4 MHz signals.
AC5
Used with the MRC. Can also be used for AF and OSC.
Power supply
VCC
8V
VCC1
5V
VCC2
0.1 V / 0.7 V / 2 V / 4 V
VCC3
0.1 V / 0.6 V / 2 V
SD, stereo, seek/stop
These levels
must be variable.
Keyed AGC, Mute ATT
HCC, SNC, SASC (MRC)
• Switches
Parameter
ON
SW1
AM/FM switching. The FE VCC is supplied to pin 62.
SW2
FM IF switching. Pin 51/FE output
SW3
For conversion gain testing
SW4
For switching between noise canceler input and IF output + noise canceler.
SW5
High-speed SD
SW6
SEEK/STOP (IF BUFF ON/OFF)
SW7
SW8
SW9
For pilot cancellation testing
SW10
Mute off (pin 33)
OFF
FM
AM
FE IF OUT (A)
AC3 (B)
Conversion gain measurement (A)
Other/purposes
AC1 (A)
Other/purposes
High-speed SD
Other/purposes
STOP
Seek (IF buffer output)
MUTE ATT 200 kΩ
MUTE 200 kΩ
OFF
MUTE ATT 30 kΩ
MUTE 30 kΩ
OFF
When pilot cancellation is used
When pilot cancellation is not used
MUTE OFF
MUTE ON
• Trimmers (variable resistors)
VR1
Separation adjustment
VR2
Pilot cancellation adjustment
Test Points
• DC voltages
VD1
FM RF AGC voltage
Pin 2
VD2
AM/FM SD, AM Tweet, FM stereo indicator
Pin 26
VD3
AM/FM S-meter
Pin 24
VD4
MRC output
Pin 27
VD5
Mute drive output
Pin 33
VD6
AM antenna damping voltage
Pin 46
VD7
N.C. Gate time
Pin 8
• AC voltages
VA1
AM/FM OSC Buff
Pin 4
VA2
First IF output
Pin 53 → CF → pin 51 load level (10.7 MHz)
VA3
IF counter buffer
Pin 23 (10.7 MHz/450 kHz)
VA4
MPX OUT Left ch
Pin 15 (AF)
VA5
MPX OUT Right ch
Pin 16 (AF)
No. 6655-5/54
LA1787M
Pin Descriptions
Pin No.
Function
Description
Equivalent circuit
VCC
62 pin
ANT
RF
AGC
1
Antenna damping drive
1000pF
An antenna damping current flows
when the RF AGC voltage (pin 2)
reaches VCC – VD.
300Ω
100Ω
1
100Ω
1000pF
A13555
VCC
FET
2nd GATE
2
RF AGC
+
Used to control the FET
second gate.
12kΩ
2
ANT
N
AGC
DET
DAMPING
DRIVER
W
AGC
DET
VCC
KEYED
AGC
A13556
3
F.E.GND
VCC
4
4
OSC
Oscillator connection
25pF
2kΩ
VT
20pF
A13557
7
VCC
7
AM OSC
AM first oscillator
This circuit can oscillator up to the
SW band.
An ALC circuit is included.
ALC
A13558
Continued on next page.
No. 6655-6/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
3kΩ
15kΩ
3kΩ
8
9
Noise AGC sensitivity
AGC adjustment
After setting up the medium field
(about 50 dBµ) sensitivity with the
noise sensitivity setting pin (pin 8),
set the weak field (about 20 to
30 dBµ) sensitivity with the AGC
adjustment pin (pin 9)
200Ω
8
9
3kΩ
+
0.47µF
1MΩ
0.01µF
A13559
0.01µF
13
11
12
Memory circuit connection
6800pF
12
3.9kΩ
11
VCC
Recording circuit used during
noise canceller operation.
Differential
amp
Gate
circuit
LPF
A13560
VCC
30kΩ
13
Pilot input
PLL
Pin 13 is the PLL circuit input pin.
N.C
12
13
0.01µF
A13561
14
N.C, MPX, MRC, GND
Ground for the N.C., MPX, and
MRC circuits.
Continued on next page.
No. 6655-7/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
VCC
15
16
MPX output (left)
MPX output (right)
Deemphasis
50 µs: 0.015 µF
75 µs: 0.022 µF
3.3kΩ
3.3kΩ
15
16
0.015µF
0.015µF
A13562
VCC
20kΩ
17
Pilot canceller signal output
Adjustment is required since the
pilot signal level varies with the
sample-to-sample variations in
the IF output level and other
parameters.
6.7kΩ
10kΩ
17
18
0.01µF
100kΩ
A13563
VCC
18
Pilot canceller signal output
Pin 18 is the output pin for the
pilot canceller signal.
1.5kΩ
17
18
0.01µF 100kΩ
A13564
Continued on next page.
No. 6655-8/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
DECODER
Composite
signal
19
Separation
adjustment pin
5kΩ
4kΩ
Use a trimmer to adjust the
subdecoder input level.
(The output level is not modified in
mono and main modes.)
19
30kΩ
0.047µF
A13565
CSB
912
JF108
20
VREF
20
VCO
The oscillator frequency is 912 Hz.
KBR-912F108
(Kyocera Corporation)
CSB-912JF108
(Murata Mfg. Co., Ltd.)
10pF
A13566
VREF
15kΩ
PHASE COMP.
PHASE COMP.
+
15kΩ
19kΩ
21
22
+
+
21
22
A13567
Continued on next page.
No. 6655-9/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
4.9V
23
IF counter buffer seek/stop
switching
This pin functions both as the IF
counter buffer (AC output) and as
the seek/stop switch pin.
The voltage V23 switches
between the following three
modes.
During FM reception:
5 V: Seek mode
2.5 V: Forced SD mode
0 V: Reception mode
AM reception
(two modes: 0 and 5 V)
5 V: Seek mode
0 V: Reception mode
+
–
50kΩ
+
–
AM MUTE
1.3V
VCC
IF counter
buffer
10kΩ
+
–
SW
150Ω
50F
SD
23
51kΩ
STOP
IF
BUFF.
Forced SEEK
SD: 2.5V 5V
A13568
VCC
FM
S-meter
24
32
AM/FM signal meter
Dedicated FM signal meter
Fixed-current drive signal meter
output
In AM mode, pin 32 outputs a
1-mA current. Thus the HCC
circuit is turned off.
32
10kΩ
AM
S-meter
24
10kΩ
AM/FM
SW
Outputs a 1-mA
current during AM
reception
MRC
AM/FM
SW
A13569
26
Stereo indicator for the SD pin
The voltage V23 switches
between three modes as follows.
FM reception:
5 V: The SD pin operates linked
to the IF counter buffer.
2.5 V: Forced SD mode: operates
as the SD pin.
0.7 V: Reception mode: stereo
indicator
AM reception: (two modes: 0 and 5 V)
5 V: Operates as the seek SD pin.
0 V: Reception mode. Not used.
AM/FM
SD
Stereo
indicator
Seek/stop
switching
26
100kΩ
VDD
A13570
Continued on next page.
No. 6655-10/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
VCC
VCC
C2
+
2µA
27
27
MRC control voltage time
constant
The MRC detector time constant
is determined by a 100 Ω resistor
and C2 when discharging and by
the 2-µA current and C2 when
charging.
100Ω
Pin 28
A13571
VREF
28
SNC control input
The sub-output is controlled by a
0 to 1-V input.
28
A13572
VREF
The high band frequency output is
controlled by a 0 to 1-V input.
29
HCC control input
It can also be controlled by the
MRC output.
Use a resistor of at least 100 kΩ
when controlling with the pin 32
FM S-meter signal.
32
29
+
1µF
A13573
Continued on next page.
No. 6655-11/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
VCC
FM
detector
output
31
30
31
Noise canceller input
Pin 30 is the noise canceller input.
The input impedance is 50 kΩ.
AM/FM detector output
Pin 31 is the AM and FM detector
output
In FM mode, this is a lowimpedance output.
In AM mode, the output
impedance is 10 kΩ.
To improve the low band
separation, use a coupling
capacitor of over 10 µF.
10kΩ
VCC
1µF
AM
detector
+
30
Noise
canceller
50kΩ
4.2V
A13574
VCC
32
32
IF S-meter output and MRC
DC input
FM S-meter output block
MRC AC input block
Adjust the external 1-kΩ resistor
to attenuate the MRC AC input
and control the circuit.
10kΩ
+
1µF
1kΩ
MRC input
A13575
C1
+
0.1µF
•The muting time constant is
determined by an external RC
circuit as described below.
Attack time: TA = 10 kΩ × C1
Release time: TR = 50 kΩ × C1
33
Mute drive output
•Noise convergence adjustment
The noise convergence can be
adjusted when there is no input
signal by inserting a resistor
between pin 33 and ground.
•Muting off function
Ground pin 33 through a 4-kΩ
resistor.
33
VCC
50kΩ
MUTE
AMP.
SEEK
OFF
SOFT
MUTE
10kΩ
HOLE
DET
Band
muting
50kΩ
SD circuit
A13576
Continued on next page.
No. 6655-12/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
0.1µF
R1
VREF
VCC
C
37
•Null voltage
When tuned, the voltage between
pins 34 and 37, V34 – 37, will be 0 V.
The band muting function turns
on when |V34 – 37| ≥ 0.7 V.
35
34
Quadrature
detector
HOLE
DET
390Ω
AGC
QD output
QD input
VREF
36
VCC
•The resistor R1 determines the
width of the band muting function.
Increasing the value of R1
narrows the band.
Reducing the value of R1 widens
the band.
34
35
36
37
R2
3pF
V37 = 4.9 V
1kΩ
IF limitter amplifier
Band
muting
A13577
R
SD ADJ
38
38
FM SD ADJ
A 130-µA current flows from pin
38 and, in conjunction with the
external resistance R, determines
the comparison voltage.
130µA
+
–
SD
Comparator
24
S-meter
A13578
S-meter
24
6.4kΩ
3.6kΩ
39
Keyed AGC
AM stereo buffer
The keyed AGC operates when
the voltage created by dividing the
pin 24 S-meter output voltage by
the 6.4 and 3.6 kΩ resistors
becomes lower than the voltage
determined by the resistor
between pin 39 and ground.
This pin also is used as the AM
stereo IF buffer pin.
Comparator
KEYED
AGC
+
–
39
1.3V
90µA
VCC
AM IF out
50pF
150Ω
A13579
Continued on next page.
No. 6655-13/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
VCC
20kΩ
+
41
HCC capacitor
20kΩ
The HCC frequency characteristics
are determined by the external
capacitor connected at this pin.
41
2200pF
A13580
This pin is used to change the
frequency characteristics of the
unneeded audio band under
100 Hz in AM mode to produce
a clear audio signal.
VCC
C
42
42
AM L.C. pin
Note: The LC capacitor must be
connected between this pin
and VCC (pin 40).
This is because the detector
circuit operates referenced
to VCC.
VCC
DET
50kΩ
1kΩ
+
–
50kΩ
The cutoff frequency fC is
determined by the following
formula.
1kΩ
A13581
fC = 1/2π × 50 kΩ × C
VCC
19kHz∠0°
BIAS
30kΩ
43
Pilot detector
Inserting a 1-MΩ resistor between
pin 43 and VCC will force the IC
to mono mode.
30kΩ
+
30kΩ
43
1µF
+
A13582
Continued on next page.
No. 6655-14/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
+
0.022µF
240kΩ
42
44
IF AGC
G1; Used for time constant
switching during seeks.
• Reception
τ = 2.2 µF × 300 kΩ
• Seek
τ = 2.2 µF × 10 Ω
The external capacitors are
connected to VCC.
This is because the IF amplifier
operates referenced to VCC.
VCC
C
2.2µF
44
VCC
DET
50kΩ
50kΩ
IF
AGC
G1
SEEK
ON
10Ω
A13583
Pin 40 VCC
45
Pin 40 VCC
45
IF output
The IF amplifier load
DET
A13584
VCC
50pF
46
100Ω
46
AM antenna damping
drive output
Wide band AGC input
I46 = 6 mA (maximum)
This is the antenna damping
current.
20kΩ
VCC
W.AGC AMP.
ANT DAMPING
DRIVER
A13585
Continued on next page.
No. 6655-15/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
30kΩ
R
47
VCC
FM muting on level
adjustment
140µA
+
–
47
Modify the value of the external
resistor to adjust the muting on
level.
Pin 24
Inverter
MUTE
A13586
VCC
5.6V
48
57
RF AGC bypass
RF AGC
RF AGC rectification capacitor
The low frequency distortion is
determined as follows:
Increasing C48 and C57 improves
the distortion but makes the
response slower.
Reducing C48 and C57
aggravates the distortion but
makes the response faster.
10kΩ
48
+
–
+
Antenna
damping
3.3µF
For AGC use
57
+
47µF
A13587
2.6V
50
51
IF bypass
FM IF input
Due to the high gain of the limiter
amplifer, care must be taken when
choosing the grounding point for
the limiter amplifer input capacitor
to prevent oscillation.
10kΩ
10kΩ
50
0.022µF
330Ω
51
IF in
A13588
2kΩ
100Ω
52
IF input
The input impedance is 2 kΩ.
52
A13589
Continued on next page.
No. 6655-16/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
VCC
IF OUT 53
• Input and output pin or the first
IF amplifier
• Inverting amplifier
53
56
IF amplifier output
IF amplifier input
300Ω
300Ω
V56 = 2 V
Input impedance: RIN = 330 Ω
2.75V
V53 = 5.3 V
Output impedance
ROUT = 330 Ω
IF IN 56
A13590
Pin 40 VCC
Pin 40 VCC
54
54
49
Mixer output: 130 µA
Mixer input
OSC
The mixer coil connected to the
pin 54 mixer output must be
wired to VCC (pin 40).
The pin 49 mixer input
impedance is 330 Ω
49
330Ω
A13591
62 pin
VCC
W-AGC
N-AGC
Pins 55 and 58 include built-in
DC cut capacitors.
The AGC on level is determined
by the values of the capacitors
C1 and C2.
55
58
W-AGC IN
AM SD ADJ
N-AGC IN
Muting attenuation
adjustment pin
Pin 55 functions as the SD
sensitivity adjustment pin in
AM mode.
The output current I55 is 50 µA,
and V55 varies depending on the
value of the external resistor.
The SD function operates by
comparing V55 with the S-meter
voltage.
55
30pF
C1
MIX
IN
50pF
58
C2
50µA
MIX
OUT
+
–
AM SD
Signal meter
A13592
Continued on next page.
No. 6655-17/54
LA1787M
Continued from preceding page.
Pin No.
Function
Description
Equivalent circuit
1ST.IF
OSC
59
Double balanced mixer
Pins 59 and 60 are the mixer
10.7-MHz output
VCC
60
59
60
Mixer output
63
64
Mixer input
Pins 63 and 64 are the mixer
input.
This is an emitter insertion type
circuit, and the amount of
insertion is determined by the
capacitors C1 and C2.
Note:The lines for pins 63 and 64
must be kept separated from
the lines for pins 59 and 60.
30Ω
VCC
C1
63
RF AMP
5pF
C2
64
5pF
620Ω
620Ω
A13593
Pin 6 functions both as the FM
front end VCC and the AM/FM
switching circuit.
6
Front end VCC AM/FM
switching
V6 voltage
VCC
SD
+
–
+
FM.F.E
AGC 100kΩ
Mode
When 8 V → FM
510Ω
6
8V
OPEN → AM
AM/FM
switching circuit
3.3V
3
GND
A13594
AM 1st
MIX
to RF
Amp.
62
62
1st MIX
INPUT
First mixer input
The input impedance is about
10 kΩ.
10kΩ
2.1V
A13595
10kΩ
5.6V
10
AM 2nd OSC
Crystal oscillator circuit
The Kinseki, Ltd. HC-49/U-S and
a CL of 20 pF must be used.
20pF
to 2nd
MIX
33pF
10
X tal
A13596
No. 6655-18/54
+
10kΩ
VREF
AM LC
PILOT DET
1µF
0.022µF
2200pF
100µF
0.22µF
11kΩ
IF7
2.2µF
3.3µF
QD IN
QD OUT
AFC IN
0.47µF
FM SD ADJ. 30kΩ
KEYED AGC 6.8kΩ
0.47µF
MUTE DRIVE
CHCC
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
1µF
32
1µF
15pF
15pF
50
0.022µF
49
31
NC-IN
30
100kΩ
47µF
51
29
GND
52
28
53
27
26
100kΩ
54
55
2.7kΩ
56
25
5V
24
AM/FM
S-METER 0.47µF
330Ω
57
23
22
59
58
21
60
61
20
0.022µF
19
+
–
62
18
17
100kΩ
18pF
63
SEP.ADJ
0.022µF
100F 100kΩ
30kΩ
AM
OSC
N.C.MPX
GND
0.015µF
0.015µF
FM/AM VSM
1000pF
ANT D
RF AGC
FE GND
18pF
OSC
10kΩ
1000pF
100kΩ
39pF
9pF
100kΩ
LEFT CH.
300pF
10µF
10µF
AM VCC
AM ANT IN
AM RF GND
FM ANT IN
FM/AM VT
FM GND
2kΩ
AM/FM OSC BUFF
25pF
20pF
0.022µF
0.022µF
10.26MHz
1µF
10µF
10µF
RIGHT CH.
NC MPX GND
0.022µF
1MΩ
0.01µF
0.47µF
3SK263 180Ω
100kΩ
64
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
FMIF AM GND
FMIF AM NC MPX VCC
MPX
OUT
200kΩ
68pF
2.2kΩ
240kΩ
240kΩ
100kΩ
100kΩ
10kΩ
1kΩ
4.7kΩ
51kΩ
22kΩ
22kΩ
22kΩ
10kΩ
0.01µF
3SK583
100pF
100pF
100pF
100pF
51kΩ
1.5kΩ
+B
12V
10µF
GND
22kΩ
22kΩ
100kΩ
10kΩ
100µF
7
6
14
15 AM IN
20
19 VSS
7.2MHz
CE
CI
CL
17 VDD
18 PD
DO
16 FM IN
1
2
3
4
5
8
LC7216M
9
13
FM/AM 10
10kΩ
1kΩ
22kΩ
100kΩ
12
11
100µF
5.6V
SEEK→AM/FM SD
STOP→FM ST IND.
9.1V
0.022µF
VCC
+
+
+
+
TO AM STEREO
(IF OUT)
+
+
10kΩ
0.1µF
240kΩ
RFAGC
1µF
HCC
1kΩ
1MH
1kΩ
0.022µF
30Ω
0.22µF
+
50kΩ AM LEVEL
ADJ
DET OUT
100µH
+
0.022µF
100kΩ
FM
100µH
+
MUTE
AMP
Q.DET
METER
ANT
D
OSC
OSC
BUFF
15pF
FM IF IN
FC18
220Ω
30MH
SNC
DC-C AFC
DET CLAMP
L.C.
8200pF AM HC
IF limiter
amplifier
+
BUFF
100Ω
MUTE
DRIVE
HOLE
DET
FMVSM
FM SD
AMVSM
AM SD
IF
AGC
AM IF IN
MRC
+
DET
510kΩ
+
AM SD ADJ
AM MIX OUT
FM WB AGCIN
1µF
IF BUFF
FM IF OUT
10kΩ
SNC
MIX
HCC
IF AM/FM
REG
SW
TWEET
RF AGC
WB AGC
20kΩ
VCO
GND
FE IF IN
FF
19k<90k
VCO
STOP
SEEK
SW
AM FM
VREF
MAIN
HC
SD/ST
IND
+
INPUT
W.B.AGC
PHASE
COMP
62pF
5.6kΩ
FF
19k<0
AMP
RF AGC
MUTE ATT
LPF
HPF
0.047µF 20kΩ
P-CAN
1µF
CSB912JF108
TRIG
PILOT
DET
MIX
FEVCC
KEYED
AGC
VCC 30Ω
FF
GATE
TRIG
AGC
0.01µF
6800pF
+
SUB MAT
DEC RIX
5pF
10pF
30kΩ
FF
38k<0
NOISE
AM/FM
0.022µF
AMP
VCC
5pF
+
+
0.022µF
0.22µF
+
ANTD
0.022µF
30kΩ
AMP
PICAN
INPUT
BUFF
8pF
30Ω
18pF
COUNTER
BUFF
AM
1ST
OSC
1000pF
ANT
D
5pF
22pF 22pF
GND
100Ω
0.022µF
0.01µF
PI.CAN ADJ
1000pF
200kΩ
0.1µF
1µF
2.2kΩ
10kΩ
L
0.22µF
+
22pF
+
GND
+
+
+
30kΩ
+
+
R
1kΩ
100pF
CE
CI
CL
DO
RDS
ADC
MUTE
LC867148
SD/MONO
ST
R ON
A13597
LA1787M
Block Diagram
No. 6655-19/54
22pF
AC2
SG2
VD6
JIS
DUMMY
15pF
65pF
100µH
6.8mH
50Ω 30Ω
0.022µF
SW8
30kΩ
30Ω
FC18
47µF
AC1
SG1
SW7
ANTD
0.022µF
0.022µF
+
50Ω
VD1
0.022µF
0.022µF
1000µF
25Ω
510Ω
100µH
1mH
18pF
FM IF OUT
AM IF IN
3pF
VCC
100Ω
0.022µF
100Ω
5pF
5pF
64
63
62
61
60
59
58
57
56
GND
FEVCC
MUTE ATT
10pF
FE IF IN
FM WB AGCIN
55
54
53
52
51
FM IF
IN
50
0.022µF
+
1
ANT
D
AM/FM
47
2
MIX
+
MIX
RFAGC
48
49
SW3
330Ω
AM SD ADJ
AM MIX OUT
20kΩ
50Ω
100kΩ
200Ω
30Ω
1.6kΩ
200kΩ
330Ω
AC3
SG3
39pF
100kΩ
50Ω
IF IN
B
SW2 ( i )
MIX A
FM VCC
3.3µF
ANT D
300Ω
FM GND
VT
+
20pF
3
BUFF
RF AGC
44
+
L.C.
4
OSC
BUFF
AM
1ST
OSC
VA1
5
KEYED
AGC
AM FM
VREF
7
6
8V
SW1
20kΩ
TRIG
AGC
+
40
0.22µF
– +
LPF
38
MAIN
HC
VCO
STOP
HCC
SNC
HOLE
DET
FF
FF
38k<0
FF
19<0
FF
19<90
k
MRC
3pF
VCC
14
0.1µF
VCO
15
16
MPX
OUT
SUB MA
DEC TRIX
P-CAN
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
1µF
+
0.22µF
0.01µF
PI.CAN ADJ
VR2
100kΩ
VR1
SEP.
ADJ
SW9 20kΩ
0.047µF 20kΩ
1µF
CSB912JF108
+
5.6kΩ
3pF
B
8V
0.022µF
SW5
50kΩ
VCC3
PG1
(AC1)
AC5
VCC2
VA3
SW6
VA8
VD3
VCC2
SEEK→AM/FM SD
STOP→AM ST BUFFER
FM ST IND.
VD2
VD4
SNC
HCC
NC-IN
FM/AM IFBUFF.
50kΩ
1µF
MRC-IN
4.3kΩ
VD5
8V
VCC
SW4 (T)
A
AM LEVEL ADJ
8200pF AM HC
AM/FM
S-METER 0.47µF
GND
SNC
HCC
NC-IN
+
DET OUT
FM S-METER
MUTE DRIVE
33
+
TRIG
PHASE
COMP
34
+
PILOT
DET
VA7
+
VA6
10µF
VA9
8V
0.022µF
0.47µF
AFC IN
MUTE
DRIVE
MUTE
AMP
35
DC-C AFC
DET CIAMP
Q.DET
36
10kΩ
37
0.1µF
VREF
10
11
12
13
AM
OSC
+
6800pF 0.01µF
39
QD IN
+
10µF
SW10
10.26MHz
X TAL
VCC
8
GATE
HPF
9
FMVSM
FM SD
IF limiter
amplifier
41
IF BUFF
AMVSM
AM SD
42
FF FM/AM
REG
SW
TWEET
IF
DET
AGC
BUFF
0.022µF
240kΩ
+
43
PILOT DET
1µF
OSC
OSC
BUFF
45
RF AGC
W.B. AGC
ANT
D
46
W.B.AGC
FE GND
15kΩ
RF AGC
MUTE OR ADJ
180kΩ
30kΩ
50Ω
1µF
IF7
5pF
QD OUT
AM LC
300pF
100µF
0.01µF 10kΩ
1MΩ
2.2µF
25pF
20pF
AM/FM OSC BUFF
2200pF
CHCC
10kΩ
0.022µF
0.022µF
0.47µF
10kΩ
0.015µF
VA2
1MΩ
1µF
IF OUT
10kΩ
6.8kΩ KEYED AGC
22kΩ FM SD ADJ.
10kΩ
0.022µF
10kΩ
100kΩ
VCC
N.C.MPX GND
+
0.015µF
+
LEFT CH.
+
RIGHT CH.
+
1MΩ
100kΩ
+
+
100kΩ
GND
A13598
5V
VCC1
LA1787M
AC Characteristics Test Circuit
+
+
No. 6655-20/54
LA1787M
Test Conditions
Parameter
Current drain
Demodulation output
Pin 31 demodulation output
Channel balance
Total harmonic distortion (FM)
Symbol
Switch states
SW1
SW2
SW3
SW4
SW5
SW6
SW7
SW8
SW9
SW10
ICCO-FM
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
VO-FM
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
VO-FM31
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
CB
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
THD-FMmono
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
—
Signal-to-noise ratio: IF
S/N-FM IF
ON
b
OFF
b
—
ON
OFF
OFF
ON
AM suppression ratio: IF
AMR IF
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
Att-1
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
—
Muting attenuation
Separation
Att-2
ON
b
OFF
b
—
ON
OFF
OFF
ON
Att-3
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
Separation
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
Stereo on level
ST-ON
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
Stereo off level
ST-OFF
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
THD-Main L
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
PCAN
ON
b
OFF
b
—
ON
OFF
OFF
OFF/ON
—
Main total harmonic distortion
Pilot cancellation
AttSNC
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
HCC output attenuation 1
SNC output attenuation
AttHCC-1
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
HCC output attenuation 2
AttHCC-2
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
Vi-lim
ON
b
OFF
b
—
ON
OFF
OFF
ON
ON
Input limiting voltage
Muting sensitivity
Vi-mute
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
SD sensitivity 1
SD-sen1 FM
ON
b
OFF
b
OFF
OFF
OFF
OFF
ON
—
SD sensitivity 2
SD-sen2 FM
ON
b
OFF
b
ON
OFF
OFF
OFF
ON
—
VIFBUFF-FM
ON
b
OFF
b
OFF
OFF
OFF
OFF
ON
—
VSM FM-1
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
VSM FM-2
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
VSM FM-3
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
VSM FM-4
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
Muting bandwidth
BW-mute
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
Mute drive output
VMUTE-100
ON
b
OFF
b
—
ON
OFF
OFF
ON
—
N-AGC on input
VNAGC
ON
a
ON
b
—
ON
OFF
OFF
—
—
W-AGC on input
VWAGC
ON
a
ON
b
—
ON
OFF
OFF
—
—
Conversion gain
A.V
ON
a
ON
b
—
ON
OFF
OFF
—
—
VOSCBUFFFM
ON
a
ON
b
—
ON
OFF
OFF
—
—
τGATE1
ON
—
OFF
a
—
ON
OFF
OFF
—
—
SN
ON
—
OFF
a
—
ON
OFF
OFF
—
—
SN-NC
ON/OFF
—
OFF
a
—
ON
OFF
OFF
—
—
VMRC
ON
—
OFF
b
—
ON
OFF
OFF
—
—
—
IF counter buffer output
Signal meter output (FM)
Oscillator buffer output
Gate time 1
Noise sensitivity
NC effect
MRC output
MRC operating level
MRC-ON
ON
—
OFF
b
—
ON
OFF
OFF
—
Practical sensitivity
S/N-30
OFF
—
OFF
b
ON
ON
—
—
—
—
Detection output
VO-AM
OFF
—
OFF
b
ON
ON
—
—
—
—
Pin 31 detection output
VO-AM31
OFF
—
OFF
b
ON
ON
—
—
—
—
AGC F.O.M.
VAGC-FOM
OFF
—
OFF
b
ON
ON
—
—
—
—
Signal-to-noise ratio
S/N-AM
OFF
—
OFF
b
ON
ON
—
—
—
—
Total harmonic distortion (AM)
THD-AM
OFF
—
OFF
b
ON
ON
—
—
—
—
VSM AM-1
OFF
—
OFF
b
ON
ON
—
—
—
—
VSM AM-2
OFF
—
OFF
b
ON
ON
—
—
—
—
VOSCBUFF AM-1
OFF
—
OFF
b
ON
ON
—
—
—
—
W-AGCsen 1
OFF
—
OFF
b
ON
ON
—
—
—
—
W-AGCsen 2
OFF
—
OFF
b
ON
ON
—
—
—
—
SD-sen1 AM
OFF
—
OFF
b
OFF
OFF
—
—
—
—
SD-sen2 AM
OFF
—
OFF
b
OFF
OFF
—
—
—
—
VIFBUFF-AM
OFF
—
OFF
b
OFF
OFF
—
—
—
—
Signal meter output (AM)
Oscillator buffer output
Wide band AGC sensitivity
SD sensitivity
IF buffer output
No. 6655-21/54
LA1787M
Usage Notes
1. Notes on VCC and Ground
Pin 40
VCC for the FM IF, AM, NC, MPX, and MRC blocks
Pin 25
Ground for the FM IF and AM blocks
Pin 14
Ground for the NC, MPX, and MRC blocks
Pin 61
VCC for the FM front end, AM first mixer, and first oscillator blocks
* Pin 6
VCC for the FM front end and AGC blocks, and the AM/FM switching pin
Pin 3
Ground for the FM front end, first mixer, and first oscillator blocks
*: When applying the VCC voltage to pin 6, that voltage must not exceed the pin 40 and pin 61 VCC voltages.
(This condition must be checked carefully when first applying the pin 6 voltage.)
2. Notes on AM Coil Connection
The VCC used for the first oscillator coil connected to pin 7 must be at the same potential as pin 61.
Connect to the IFT connected with pin 45, and to the MIX coil connected with pin 54. VCC must be at the same potential
as pin 40.
3. AM/FM Switching
Pin 6 is also used as the FM front end and RF AGC VCC
Pin 6 voltage
Mode
8
FM
OPEN
AM
Fig. 1
LA1787M Overview
1. Notes on the LA1781M, LA1784M, and LA1787M
The LA1784M is a version of the LA1781M that uses an external oscillator circuit, and has the same characteristics as
the LA1781M.
The LA1787M is a version of the LA1784M that features improved characteristics.
LA1781M
LA1784M
This product is a version of the LA1781M
with the oscillator circuit removed. It
supports the use of an external oscillator
circuit.
It has the same characteristics as the
LA1781M.
LA1787M
The LA1787M features improved
characteristics over the LA1781M
and LA1784M.
No. 6655-22/54
LA1787M
2. Modified circuits
The following characteristics have been improved over those of the The LA1784M.
• The AM adjacent channel interference characteristics (∆40 kHz) have been improved.
• The AM S-meter curve slope has been increased.
• The FM separation temperature characteristics have been improved.
• The stereo indicator sensitivity has been improved.
• The FM oscillator circuit has been omitted.
(1) AM interference characteristics improvement
The second signal interference and suppression have been improved for adjacent channels (±40 kHz) by increasing
the AM second mixer input dynamic range.
(2) The AM S-meter curve slope has been increased.
The slope of the AM S-Meter curve has been increased from that of the LA1781M and LA1784M.
AM S-Meter Voltage
7
S-meter voltage — V
6
5
M
87
LA1780M
7
A1
L
4
3
M
81
17
LA
2
1
0
–20
0
20
40
60
80
100
120
140
Antenna input — dBµ
(3) FM separation temperature characteristics improvement
The temperature characteristics have been improved, the amount of change in the separation due to drift when at
power on has been stabilized. This makes it easier to adjust the separation.
Change in Separation (LA1787M): First IF Input
60
55
55
Change in separation — dB
Change in separation — dB
Change in Separation (LA1781M): First IF Input
60
50
45
40
35
0
1
2
Time after power on — minutes
3
50
45
40
35
0
1
2
3
Time after power on — minutes
No. 6655-23/54
LA1787M
(4) Stereo indicator sensitivity improvement
The stereo indicator sensitivity (on/off) is equivalent to that of the LA1780M
Stereo on level
Stereo off level
LA1781M/1784M
4.1%
3.1%
LA1787M/1780M
2.6%
1.6%
(Typical value)
*: The pilot level such that the stereo indicator goes on or off for a 10.7 MHz unmodulated IF input.
(5) FM oscillator circuit removed
The internal FM oscillator circuit provided in the LA1781M has been removed. The FM oscillator level can be
adjusted by constructing an external circuit block.
*: However, this requires 4 more external parts than the LA1781M: 1 transistor and 3 resistors/capacitors.
IC internal
VCC
IC internal
VCC
VCC
4
4
Vt
Vt
A13600
A13601
LA1780M/1781M FM OSC
LA1787M/1784M FM OSC
3. Gain distribution
The table below shows the gain distribution of the LA1780M, LA1784M, and LA1787M. (These are measured
values.) Compared to the LA1784M, the total gain is lower.
1st MIX (10.7)
1st IF (10.7)
2nd MIX (450)
2nd IF (450)
LA1780M
10 dB
3.3 dB
3.2 dB
69 dB
LA1784M
7.5 dB
13 dB
7 dB
66 dB
LA1787M
7.5 dB
3.5 dB
8.6 dB
67 dB
First mixer
: No circuit changes from the LA1784M.
First IF amplifier
: Equivalent to the LA1780M circuit. (The gain is lower than that in the LA1781M and LA1784M.)
Second mixer
: The mixer circuit has been modified to improve adjacent channel suppression and interference.
Second IF amplifier
: Equivalent to the LA1780M circuit.
No. 6655-24/54
LA1787M
4. Changes to applications
Component values that change from LA1781M/LA1784M applications
(Since the total AM gain has changed in the LA1787M)
• AM SD adjustment resistor (pin 55): Because Vsm is higher.
• AM level adjustment resistor (pin 31): Since the post-detection audio amplifier gain is higher than in the LA1781M
and LA1784M, the output level is also higher. This resistor must be changed
to match the set value.
• AM mixer coil (pin 54), IFT coil (pin 45) damp resistor: Since the IF block gain is increased, the mixer (pin 54) and
IFT (pin 45) coil damping must be adjusted.
• Separation adjustment resistor (pin 19): Since an internal 4 kΩ resistor has been added to the pin 19 input circuit to
improve the separation temperature characteristics, the value of the external
resistor must be reduced from that used with the LA1780M, LA1781M, and
LA1784M. (See the following page.)
DECODER
Composite Sign
Composite Sign
5kΩ
DECODER
5kΩ
Added 4 kΩ resistor
19
19
30kΩ
30kΩ
0.047µF
0.047µF
A13602
A13603
LA1787M
LA1781M/1784M
Functions
1. Notes on the FM Front End
Notes on interference rejection characteristics
• Intermodulation characteristics
The LA1787M applies two high-band AGC functions to prevent IM (the generation of intermodulation). These are
the narrow AGC (pin 58: mixer input detection type) and the wide AGC (for the pin 55 input), and this results in the
antenna frequency characteristics shown in figure 2. The levels at which the AGC functions turn on are determined
by the capacitors attached at pins 55 and 58.
∆f — AGC Sensitivity
When ∆f = 0, 98.1 MHz
AGC sensitivity — dBµ
110
100
The wide AGC
sensitivity when
pin 39 is 5 V.
90
80
70
The narrow AGC
sensitivity when
pin 39 is at ground.
60
50
–5
–4
–3
–2
–1
0
1
2
3
4
5
∆f — MHz
Fig. 2
No. 6655-25/54
LA1787M
• Notes on second-channel attenuation suppression
Keyed AGC (3D AGC) is a technique for achieving good characteristics for both intermodulation and secondchannel attenuation at the same time. When the desired signal is faint or nonexistent, the high-band AGC level will
be essentially 0, and as a result automatic tuning may malfunction and blocking oscillation may occur in the
presence of strong interfering stations. Keyed AGC helps resolve these problems.
This 3D AGC technique uses information that has the following three frequency characteristics and is a unique
Sanyo-developed system for determining the high-band AGC level.
RF and ANT circuit information: Mixer input AGC
Mixer circuit information: Mixer output AGC
CF selectivity information: S-meter output
• 3D AGC Features
Feature
Merit
Only the narrow AGC sensitivity (operation at ∆f < 1.5 MHz) is
controlled by the field strength of the desired station.
• Effective in resolving second-channel attenuation problems.
The narrow AGC sensitivity is controlled by a voltage (V 23) that is
under 0.5 V.
• Allows effective resolution of second-channel attenuation problems without
degrading three-signal characteristics.
The wide AGC can operate even when V23 = 0 (when the desired
station is not present).
• Seek operations may stop incorrectly due to the occurrence of
intermodulation.
• It is possible to prevent the occurrence of intermodulation in the RF tuning
circuit and antenna in the presence of strong interfering stations, and
blocking oscillation due to AGC operation can be prevented.
The narrow and wide AGC sensitivities can be set independently.
(See figure 3 and 4.)
• Settings can be optimized for the field conditions.
The system has two AGC systems: narrow and wide AGC.
(See figure 5.)
• Since the narrow AGC operates for the desired station and adjacent
stations, the wide AGC sensitivity can be lowered and AGC malfunction
due to local oscillator signal can be prevented.
∆f — AGC on Level (ANT input)
∆f — AGC on Level (ANT input) Fig.4
Fig.3
Pin 55 capacitor: 3 pF
110
Wide AGC on level — dBµ
Narrow AGC on level — dBµ
110
100
90
Pin 58 capacitor:
10 pF
80
70
keyed AGC
39
Pin 58 capacitor:
47 pF
60
50
–5
–3
–4
–2
–1
1
0
2
3
4
90
Pin 55 capacitor: 10 pF
80
70
keyed AGC
39
5V
60
50
5
–5
–4
–3
–2
–1
0
1
2
3
4
5
∆f — MHz
∆f — MHz
Pin 59 narrow AGC and pin 55 wide AGC input levels — dBµ
100
W-AGC, N-AGC — f
Fig.5
70
80
s
Wide AGC on level frequency characteristic
Narrow AGC on
90
level frequency
characteristics
100
110
120
130
AGC input level frequency
characteristics such that
VRFAGC (pin 2) falls under 2 V.
140
7 1.0
2
3
5
7 10
2
3
5
7 100
2
3
5
Frequency, f — MHz
No. 6655-26/54
LA1787M
3D AGC Sensitivity Characteristics
AGC sensitivity
Wide AGC sensitivity
∆F
1
2
Second-channel
attenuation improvement
Narrow AGC sensitivity
3
Desired station AGC sensitivity
4
V23 (Desired station field strength)
A12075
Fig. 6
3D AGC Sensitivity — ∆f, V23 characteristics
• The wide AGC sensitivity is determined by the antenna and RF circuit selectivity, regardless of V23.
• The narrow AGC sensitivity is determined by the following.
The total selectivity of the antenna, RF circuit, and mixer when V23 ≥ 0.5 V
The above selectivity and V23 when V23 < 0.5 V
• The improvement in the second-channel attenuation corresponds to the area occupied by the narrow AGC in the
total AGC sensitivity area.
Figure 8 on the next page shows the actual operation of the circuit.
The fu input level at which antenna damping turns on — dBµ
∆f — AGC on Level (ANT input)
110
fD = 98.1 MHz Second-channel pad
100
90
ANT IN
VIN
80
70
fu = 98.1 MHz + ∆f
60
50
–5
–4
–3
–2
–1
0
1
∆f — MHz
2
3
4
A12076
5
Fig. 7
No. 6655-27/54
LA1787M
Notes on 3D AGC (Keyed AGC)
VCC
55
W-AGC
DET
58
N-AGC
DET
90µA
S-meter
+
–
VCC
+
–
1
2
39
24
+
ANT
DUMPING
VS-meter
A11763
Fig. 8
• The antenna damping current from the pin due to the pin diode flows when the V2 pin reaches the VCC - VBE
level.
• The narrow AGC operates as follows.
When pin V39 > pin V24: The narrow AGC turns off.
When pin V39 < pin V24: The narrow AGC turns on.
No. 6655-28/54
LA1787M
• The LA1787M includes two AGC circuits in its front end block.
— Antenna input limiter using a pin diode.
— FET second gate control
The AGC input pin is pin 59, and the AGC circuit turns on when a signal of about 30 mVrms is input.
AGC activation
The pin diode drive circuit turns on when VCC – V2 is greater than or equal to about 1 V, and input limitation is
applied to the antenna circuit. In application circuits, there will be an attenuation of about 30 to 40 dB. Next, when
an adequate current flows in the antenna attenuator pin diode, the inductance falls, the FET second gate voltage
drops, the FET gm falls, and the AGC operates. The recommended FET is the Sanyo 3SK263, which is an
enhancement-type MOSFET. Therefore, full AGC is applied when the voltage, VG2-S, between the second gate and
the source is 0. Note that if a depletion-type MOSFET is used, AGC will not be applied unless VG2-S is less than 0.
V2 AGC Characteristics
Fig.9
9
fr = 98.0 Hz
VCC = 8 V
Ta = 25°C
8
6
Range where AGC level AGC level due
the AGC does due to the
to the MOSFET
not operate
pin diode:
second gate:
about 35 dB
about 35 dB
5
4
3
2
1
0
–10
0
10 20 30 40 50 60 70 80 90 100 110 120 130 140
ANT IN — dBµ
63
62
MIX VCC
60
MIX INPUT
Due to optimized device geometry, emitter current, the bias, this IC
achieves the following performance.
59
MIX OUT
64
MIX OUT
• Mixer
The mixer circuit in this IC is a double-balanced mixer with both
balanced input and balanced output.
Input circuit type
Emitter input
Input impedance: 25 Ω
MIX INPUT
V2AGC — V
7
MIX
Mixer input usable sensitivity: 15 dBµ
Mixer input IMQS: 90.5 dBµ
(For an oscillator level of 200 mVrms)
OSC
* The mixer input IMQS is defined as:
fr = 98.8 MHz, no input
fu1 = 98.8 MHz, 1 kHz, 30% modulation
fu2 = 99.6 MHz, no modulation
The interference 1 and 2
input levels such that
generated intermodulation
output signal-to-noise ratio
becomes 30 dB when an
interference signal with the
same level as the mixer input
is input, and distortion occurs
in the mixer.
Mixer circuit
A12077
Fig. 10
No. 6655-29/54
LA1787M
• Oscillator
Figure 11 shows the type of oscillator circuit used in this IC. It includes both an oscillator and an oscillator buffer.
VCC
18pF
4
25pF
AM/FM
OSC BUFFER OUT
5
VT
20pF
A12078
Fig. 11
• Figure 12 shows the type of FM first IF amplifier used in this IC. It is a differential single-stage amplifier.
330Ω
TO MIX
FM IF input
56
53
330Ω
+
330Ω
–
A12079
Fig. 12
Specifications
Input impedance: 330 Ω
Output impedance: 330 Ω
Gain: 20 dB
No. 6655-30/54
LA1787M
2. FM IF
• Notes on the FM SD and SD adjustment
The figure below presents an overview of the FM SD and the IF count buffer.
4.9V
R
+
–
R
+
–
R
Band
muting
Muting
drive
output
HOLE
CLET
STEREO
IND
S-meter
IF count buffer
+
–
39
24
FM IF
33
23
26
5V
IF count output
SD
STEREO/MONO
2.5V 5V
Fig. 13
A11759
Figure 14 shows the relationship between the FM SD, the IF count buffer output, the S-meter, and the muting drive
output.
V24
Larger
values
of R33
S-meter
V38
V33
Smaller values of R33
V33
over 0.7 V
V33
over 0.7 V
V26
5V
SD
ON
On as an
SD signal
SD
ON
Mono
Stereo
V23AC
0.7 V
OFF
IF count
buffer
OFF
IF counter output off
V23DC
5V
2.5 V
0V
RDS and other types of SD detection can be used by switching these modes.
New LA1784M functionality: For stereo input (when the V26 pin voltage is 0.7 V),
when this pin is shorted to ground (0.1 V or lower)
the IC will operate in forced mono mode.
A11758
Fig. 14
No. 6655-31/54
LA1787M
• Transient response characteristics during automatic tuning
The transient characteristics for SD and IF count buffer on/off operation are determined by the time constants of
the RC circuits attached to the following pins.
(1) Muting time constant: pin 33
(2) S-meter time constant: pin 24
(3) AFC time constant: pin 34
There are two points that require consideration when using fast tuning.
(1) The SD time constant due to the S-meter time constant
Since the current I24 (pin 24) varies with the field strength, the time constant also changes. There is no hysteresis
in the comparator.
If a smaller value is used for C24, you must select a value for C such that the AGC does not become unstable
when the pin 24 voltage is used for keyed AGC.
S-meter
10k
24
C24
A12080
Fig. 15
(2) The SD time constant due to the pin 33 muting voltage time constant
The changes in volume due to field fluctuation during weak field reception can be made smoother by setting the
attack and release times during soft muting operation.
Mute
drive
Mute
amp
10kΩ
Muting time constants
Attack: 10 kΩ × C33
50kΩ
Attack
Release: 50 kΩ × C33
Release
33
C33
A11766
Fig. 16
Antenna input such that pin 5 goes high — dBµ
SD Sensitivity Adjustment
Fig.17
50
40
30
20
10
0
6
10
14
18
22
26
30
34
Resistance between the pin and ground — kΩ
No. 6655-32/54
LA1787M
However, when testing this stop sensitivity, note that when checking the waveform on the IF count buffer output
(pin 23), there are cases, such as that shown below, where current in the test system may be seen as flowing to
ground and cause oscillation that causes the IF count buffer output to go to the output state.
F.E.
IF buffer
amp
IF
5V
0.022 µF
Test system capacitance
The 10.7 MHz feeds back through ground.
A12081
Fig. 18
• FM Muting control pin (pin 47) (R47: 30 kΩ variable resistor)
The –3 dB limiting sensitivity can be adjusted with R47.
FM Soft Muting (1)
R47 = 7.5 kΩ
Fig.19
DET out
Output,
Output noise — dB
15 kΩ
10 kΩ
20 kΩ
Noise
Antenna input — dBµ
• FM muting attenuation adjustment (pin 58)
The muting attenuation can be switched between the three levels of –20, –30, and –40 dB by the resistor inserted
between pin 58 and ground. (Note that the exact values depend on the total tuner gain.)
The noise convergence with no input is determined by the pin 58 voltage.
58
100Ω
R58
R58
A11764
Mute ATT
Open
–20 dB
200 kΩ
–30 dB
30 kΩ
–40 dB
The attenuation can be set by making R33 smaller as listed
in the table above.
33
R33
A11765
Fig. 20
No. 6655-33/54
LA1787M
FM Soft Muting (2)
FM Soft Muting (3)
Fig.21
Fig.22
R47 = 7.5 kΩ
R47 = 7.5 kΩ
DET out
DET out
10 kΩ
Output,
noise —
Output noise
— dB
dB
Output — dB
10 kΩ
Output — dB
15 kΩ
200 kΩ
20 kΩ
Noi
se
15 kΩ
30 kΩ
Nois
2 0kΩ
Antenna input — dBµ
e
Antenna input — dBµ
VCC
Quadrature detector
200 kΩ
R
Mute amp.
(VCA)
+
–
R
+
–
N-AGC
Mute
drive
Limiter
R
58
33
31
DET out
To MIX out
Open
200 kΩ
30 kΩ
Fig. 23
A11767
• FM muting off function
Forcing this pin to the ground level turns muting off.
Detector
output 0
1
When the pin is at the ground level, the noise convergence will
be 10 dB and the –3 dB limiting sensitivity will be about 0 dBµ.
20
Antenna input
A12082
Fig. 24
No. 6655-34/54
LA1787M
• Hall detection
The Hall detection function detects the level of the pin 36 quadrature input signal and then applies peak detection
to that result. The result is output from pin 33. This circuit has three effects.
(1) It assures that muting will be applied for weak inputs with an antenna input of under 5 dBµ. The amount of
attenuation is referenced to an antenna input of 60 dBµ, fm = 1 kHz, and a 22.5 kHz dev output, and is variable
from 10 dB to 40 dB when there is no input. Thus one feature of this circuit is that the weak input noise
attenuation and the –3 dB limiting sensitivity for over 5 dBµ inputs can be set independently.
Hall Detection Output — Antenna Input Characteristics Fig.25
5
Area muted by Hall detection
V38pin — V
4
3
2
1
0
–20
–10
0
10
20
30
Antenna input — dBµ
(2) When the pin 36 quadrature input is a saturated input, the pin 36 noise level (Va) is detected and a peak-hold
function is applied to pin 33 (Vb) for locations rapid field strength variations and severe multipath occurs for
fields that result in an antenna input level of over 5 dBµ.
36
33
Vb
Va
0
+
0.1µF
0
A12083
Fig. 26
(3) Unique features
One unique feature of the LA1784M is that if there are adjacent stations such that f1 = 98.1 MHz and f2 =
97.9 MHz, a search operation will not stop at 98.0 MHz. Since VAFC = 0 V and VSM = 3.6 V at 98.0 MHz in
the situations shown in figure 27 and 28, even though Hall detection would normally not operate and SD would
be high, in this IC the Hall detection circuit will operate, VMute will be set to 1.2 V (over 0.7 V) and the SD
signal will go low, thus preventing incorrect stopping of the search.
No. 6655-35/54
Fig.27
f1
f2
ANT
IN
0
Pin 24, VSM — V
–1
6
4
2
0
6
4
2
f2 = 97.9 MHz, 120 dBµ
fm = 400 Hz, 22.5 kHz dev.
f1 = 98.1 MHz, 120 dBµ
fm = 1 kHz, 22. 5kHz dev.
0
8
Pin 26 (SD) — V
Unique Features of the LA1784M Hall Detection Circuit (2)
2
1
Fig.28
When the tuner is moved in 50 kHz steps.
With a 51 kΩ resistor between pins 37 and 34.
With the SD sensitivity adjusted to be 20 dBµ.
0
–1
6
4
2
0
97.7
97.9
97.8
98.0
98.1
98.2
Pin 24, VSM — V
1
When the tuner is moved in 50 kHz steps.
With a 51 kΩ resistor between pins 37 and 34.
With the SD sensitivity adjusted to be 20 dBµ.
Voltage between pins 37 and 34, VAFC — V
Pin 33, VMute — V
Unique Features of the LA1784M Hall Detection Circuit (1)
2
6
4
2
0
6
4
2
0
f2 = 97.9 MHz, 40 dBµ
fm = 400 Hz, 22.5 kHz dev.
f1 = 98.1 MHz, 40 dBµ
fm = 1 kHz, 22.5 kHz dev.
8
Pin 26 (SD) — V
Voltage between pins 37 and 34, VAFC — V
Pin 33, VMute — V
LA1787M
6
4
2
0
97.7
98.3
Frequency, fr — MHz
97.8
97.9
98.0
98.1
98.2
98.3
Frequency, fr — MHz
• Notes on the quadrature input level
When a strong field is being received the quadrature signal input (pin 36) requires a 200 mV rms input, and the
detection transformer and the damping resistor between pins 36 and 37 must be designed.
(We recommend the Sumida SA-208 transformer and a 10 kΩ resistor between pins 36 and 37.)
When the pin 36 input level falls below 160 mV rms, the Hall detection circuit operates and the pin 33 mute drive
output voltage increases. Therefore, when pin 36 input is from 160 to under 200 mV rms during strong field
reception, the muting circuit may or may not operate due to sample-to-sample variations between individual ICs.
Furthermore, the SD function may not operate, and the audio output level may be reduced. Incorrect operation due
to sample-to-sample variations and temperature characteristics can be prevented by keeping the pin 36 voltage at
200 mVrms or higher.
Pin 33 VMute — QD Input Level
SA208 + LA1787M IF Input Characteristics
Fig.29
6
Fig.30
4 0.8
With pins 34 and 37 shorted.
With 5 V applied to pin 24.
3 0.6
5
THD — %
Vmute — V
2 0.4
4
3
2
75 Ω
SG
75 Ω
+
0.022 µF
1
36
10.7 MHz
0
92
94
96
37
98
102
–100 –80 –60 –40 –20
–120
With the resistor between
pins 36 and 37 open.
With a 10 kΩ resistor
between pins 36 and 37.
0
20
–0.2
–0.4
40
60
80
∆f — kHz
100 120
∆f=0→
10.7 MHz
–0.6 Voltage between pins 37 and 34
LA1888M
100
THD 1 kHz
75 kHz dev
1 0.2
–0.8 (referenced to the pin 37 voltage)
104
106
QD input level — dBµ
No. 6655-36/54
LA1787M
R36-37
Detector output Pin 36 AC level
MPX OUT
Vo
QDIN
Open
330 mVrms
235 mVrms
10 kΩ
280 mVrms
200 mVrms
• Band Muting Adjustment Procedure
The muting bandwidth can be modified as shown in figure 31 with the resistor RBW between pin 34 and 37.
Bandwidth such that the pin 33 voltage ≥ 2 V — kHz
RBW — Muting Bandwidth
Fig.31
280
RBW
+
240
+
1 µF
0.47 µF
SA208
Sumida
200
10 kΩ
37
160
36
35
34
ANT IN 98 MHz 100 dBµ
120
80
40
0
1.0
3
2
5
7
2
10
3
5
7 100
2
Resistor RBW between pins 34 and 37 — kΩ
3. AM
• AM AGC system
The LA1787M RF AGC circuit takes its input from three sources: the WIDE AGC pin (pin 46), the MIDDLE
AGC pin (pin 49) and NARROW AGC. There is also an IF AGC circuit.
RW
1st MIX 10.7MHz CF
62
RF
2nd MIX 450kHz CF
49
IF Amp.
DET
52
31
VCC
42
1st OSC
X'tal
240 kΩ
VCC
Amp.
46
IF AGC
44
2.2 µF
Middle AGC IN
Narrow AGC IN
Wide AGC IN
ANT
damping
RF AGC
57
+
47 µF
48
+
3.3 µF
Fig. 32
A11762
No. 6655-37/54
LA1787M
AM AGC f characteristics
Wide AGC
Operates for wide
band interference
Wide AGC
Operates for
wide band
interference
AGC on level
90
Middle AGC
Operates for
interference within
±70 kHz of the
received frequency.
80
70
Middle AGC
Operates for
interference within
±70 kHz of the
received frequency.
Narrow AGC
Operates at the
received frequency.
60
1000
900
800
Fig.33
100
1100
1200
Frequency — Hz
Wide Band AGC Circuit
Fig.34
30 Ω
110
50 Ω
–6dB
50 Ω
SG
Received frequency:
1 MHz
0.022 µF
46
0.022 µF
100
510 Ω
ANTD
0.022 µF
90
80
70
1.0
2
3
5
7
10
2
3
5
Pin 46 input — MHz
The wide band AGC circuit in this IC has the frequency characteristics shown above. The pin 46 input frequency
characteristics are identical to those of the RF amplifier gate. This AGC circuit serves to prevent distortion at the
FET input when a strong signal is applied to the antenna circuit. The level at which the AGC circuit turns on can be
adjusted to an arbitrary level with the wide band AGC adjustment resistor. A delayed AGC on level can be handled
by reducing the value of the adjustment resistor.
Wide band AGC adjustment resistor
0.022 µF
VCC
30 Ω
620 Ω
1MH
100 µH
FC18
57
15 pF
15 pF
+
47 µF
100 kΩ
0.022 µF
100 µH
30MH
Antenna damping on input level — dBµ
120
62
Fig. 35
A12084
No. 6655-38/54
LA1787M
• Notes on AM SD (pin 26) and the SD adjustment pin
SD and the IF buffer are operated by comparing the S-meter level (V24) and the 5 V reference voltage as shown in
figure 36.
S-meter
AM IF
Comparator
VCC
+
–
IF buff amp.
50 pF
50 µA
55
24
23
26
100 kΩ
100 kΩ
0.47 µF
0.022 µF
51 kΩ
IF buffer
5V
SD
Seek
5V
Fig. 36
A12085
Figure 37 shows the relationship between the AM SD, the IF count buffer, and the S-meter.
V24PIN
Larger
values
of R55
S-meter
V55
V26
Smaller values of R55
SD on
V23AC
OFF
IF buffer on
V23DC
5V
Pin 55: AM SD adjustment pin
0V
A11760
Fig. 37
No. 6655-39/54
LA1787M
• AM high band cut and detector output level adjustment methods
The pin 31 AM and FM tuner output has an impedance of 10 kΩ in AM mode and a few tens of Ohms in FM
mode. Therefore, R31 is used to lower the AM detector output level and C31 determines the AM high band
frequency characteristics.
VCC
FM
detector
31
R31
C31
VCC
+
AM
detector
10 kΩ
Noise
canceler
input
30
50 kΩ
A12086
Fig. 39
• AM stereo system pins
To the AM stereo decoder
VCC
GND
400 mV rms
450 kHz output
IFT
45
39
VCC
50 pF 150 Ω
Keyed AGC
IF AMP.
Fig. 40
A11761
No. 6655-40/54
LA1787M
• AM low band cut adjustment method
The AM low band frequency characteristics can be adjusted with C42, which is inserted between pin 42 and VCC.
Since the detector is designed with VCC as the reference, C42 must be connected to VCC.
Detector Output — Frequency
Fig.42
10
0.022 µF (41pin)
With no used (31pin)
VCC
0
42
50 kΩ
10 kΩ
+
AM
detector
10 kΩ
–
50 kΩ
To pin 31
10 kΩ
A12087
Detector output — dB
C42
0.022 µF (41pin)
With no used (31pin)
–10
–20
0.043 µF (41pin)
% with no used (31pin)
0.022 µF (41pin)
8200 pF (31pin)
–30
Fig. 41
fr = 1000 kHz
fm = 1 kHz, 30%
–40
0.001 2 3
5 70.01 2 3
5 7 0.1
2 3
5 7 1.0
2 3
5 7 10
Frequency — Hz
4. Noise Canceler Block
• The noise canceler input (pin 30) has an input impedance of about 50 kΩ. Check the low band frequency
characteristics carefully when determining the value of the coupling capacitor used. Note that fC will be about 3 Hz
when a 1 µF capacitor is used in the application.
• Pins 8 and 9 are used to set the noise detector sensitivity and the noise AGC. It is advisable to first set the noise
sensitivity for a medium field (an antenna input of about 50 dBµ) with pin 8 (the noise sensitivity setting pin), and
then set the AGC level for a weak field (20 to 30 dBµ) with pin 9 (the AGC adjustment pin). If the noise sensitivity
is increased, the AGC will become more effective but, inversely, the weak field sensitivity will be reduced.
Noise canceler 10 kHz overmodulation malfunction may be a problem. In particular, when an overmodulated
signal is input, the noise canceler may, in rare cases, malfunction. This is due to the fact that the IF detector output
has a waveform of the type shown in figure 43 due to the bands of the IF ceramic filters as shown below. (Here, the
antenna input is 60 dBµ, the ceramic filters are 150 kHz × 1 and 180 kHz × 2, f = 10 kHz, 180 kHz dev.) The noise
canceler reacts to the spikes (whiskers) generated due to this overmodulation, which results in distortion to the
audio output. (The spike components due to overmodulation occur due to the bands of the ceramic filters in the
tuner.) The following describes a method for resolving this problem. This incorrect operation due to
overmodulation is prevented by removing the spike components due to this overmodulation with a low-pass filter
consisting of a 1 kΩ resistor and a 2200 pF capacitor shown in figure 44. However, note that the FM separation
characteristics in the high band and the AM frequency characteristics will change.
IF audio output
f = 10 kHz,180 kHz dev
IF output
1 kΩ
Noise canceler input
+
H1 W1
2.5OU
31
2200 pF
–
30
1 µF
A12089
Fig. 44
–2.5OU
–19.00 µs
981.00 µs
Fig. 43
A12088
No. 6655-41/54
LA1787M
5. Multiplexer Block
• HCC (high cut control) frequency characteristics (pin 41)
When the HCC function operates, the frequency characteristics of the output signal are determined by the
capacitance of the external capacitor connected to pin 41.
20 kΩ
To the
matrix
VO
(dB)
41
C
A12090
Fig. 45
1
2πC × 20 kΩ
1
fC = ——————— [Hz]
2π × C × 20 kΩ
Frequency Characteristics
Fig. 46
f
(Hz)
A12091
Fig.47
10
Changes in the pin 41 capacitor capacitance (for a 100% high cut ratio)
0.001 µF
0µ
F
–10
0.0022 µF
–20
0.0047 µF
–30
F
1µ
0.0
Attenuation, HCC — dB
0
–40
–50
–60
3
VCC = 8.0 V
f = 98 MHz 100%mod
80 dBµ IN
5 7 100
2
3
5 7 1k
2
3
5 7 10k
2
3
Frequency, f — Hz
• Pilot canceler adjustment (pins 17 and 18)
Noise
30
canceler
input
–
To the
multiplexer
Fig. 48
Gate
Pilot
cancel
11
12 17
18
6800 pF 3.9 kΩ 0.01 µF 50 kΩ
A12092
The pilot canceler signal waveform (pin 19) is a 19 kHz signal that contains no third harmonic as shown in figure
48. Since this signal has the same phase as the pilot signal, no capacitor is required between pin 18 and ground.
Since it has no third harmonic component, excellent pilot cancellation can be acquired in both the left and right
channels by adjusting with a variable resistor.
No. 6655-42/54
LA1787M
• Separation adjustment (pin 19)
5 kΩ
To the
subdecoder
Larger
19
A12094
20 kΩ
0.047 µF
C
Fig. 49
A12093
The separation is adjusted by modifying the input level to the subdecoder with the variable resistor connected to
pin 19. Since only the sub-modulation level is changed by changing the variable resistor setting, the monaural
(main) output level is not changed. Furthermore, degradation of high band separation in the decoder can be avoided
if the impedance of the external capacitor (C) in the subchannel frequency band (23 to 53 kHz) is made sufficiently
smaller than the variable resistor.
6. MRC Circuit
VCC
2 µA
S-meter
100 Ω
FM
S-meter
DC buffer
MRC
30 kΩ
6.4 kΩ
10 kΩ
3.6 kΩ
24
+
QMRC
75 pF 1 kΩ
32
Noise amplifier
High-pass filter with
Fc = 70 kHz + amplifier
An external transistor equivalent
to the 2SC536 is required
Reason: A QMRC level shifter is
required to allow a simplified MRC
circuit to be used in the LA1787M.
27
+
C27
VCC
To the SNC, pin 28
A11768
Fig. 50
No. 6655-43/54
LA1787M
(1) When there is no AC noise on pin 32
V24 = V27–VBE
↑
QMRC
V27 is about 2.5 V when the antenna input is 60 dB or higher.
(2) Since the MRC noise amplifier gain is fixed, the MRC circuit is adjusted by reducing the AC input level.
32
+
Fig. 51
A11769
(3) The MRC attack and release are determined by C27 on pin 27.
Attack: 7 µA · C27 → 2 µA · C27
Release: 500 Ω · C27 → 100 Ω
Notes on the Noise Canceler
The noise canceler characteristics have been improved by implementing the circuit that determines the gate time in
logic. Since the time constant in earlier noise cancelers was determined by an RC circuit such as that shown in figure
52, the rise time shown in figure 53 was influenced by the values of the resistor and capacitor used. As a result the
noise exclusion efficiency was reduced by this delay in the rise time. In the LA1787M, this rise time was shortened by
implementing the circuit that determines the gate time in logic, allowing it to reliably exclude noise.
A11772
A11771
Fig. 52
Fig. 53
No. 6655-44/54
LA1787M
Gain Distribution (FM)
This section investigates the gain in each block in the LA1787M when the Sanyo recommended circuits are used.
(Test conditions)
Ambient temperature: 26°C
Antenna and mixer input frequency: 98.1 MHz
First and second IF input frequency: 10.7 MHz
The input levels when VSM = 2 V will be as follows.
ANT IN: 19 dBµ
MIX IN: 30 dBµ
1st IF IN: 42 dBµ
2nd IF IN: 60 dBµ
When the gains for each block are determined according to the above, the results are as follows.
RF GAIN: 11 dB
MIX GAIN: 12 dB
1st IF GAIN: 18 dB
1st IF IN 56 pin
FM
MIX IN 64 pin
RF
ANT IN
2nd IF IN 51 pin
11 dB
12 dB
18 dB
A11773
Fig. 54
No. 6655-45/54
LA1787M
(AM)
This section investigates the gain in each block in the LA1787M when the Sanyo recommended circuits are used.
(Test conditions)
Ambient temperature: 26°C
Antenna and mixer input frequency: 1 MHz
First and second mixer input frequency: 10.7 MHz
Second IF input frequency: 450 kHz
The gains at each stage will be as follows.
RF Gain (ANT IN-pin62): 17 dB
1st MIX Gain (pin62-pin56): 8 dB
1st IF Gain (pin55-pin53): 15 dB
AM
1st MIX
1st IF
2nd MIX
1st MIX
Gain
1st IF
Gain
2nd MIX
Gain
2nd IF
AM DET
RF
RF
Gain
2nd IF
Gain
A11774
Fig. 55
No. 6655-46/54
LA1787M
Input Circuits for Each Stage
[FM]
• Mixer input
• First IF input
75 Ω
0.022 µF
75 Ω
63
300 Ω 0.022 µF
56
75 Ω
64
75 Ω
VIN
Actual
measurement
fr = 10.7 MHz
A11776
A11775
• IF input
75 Ω
300 Ω
0.022 µF
51
330 Ω
75 Ω
50
0.022 µF
fr = 10.7 MHz
A11777
[AM]
• First mixer input
50 Ω
• Second mixer input
0.022 µF
62
50 Ω
50 Ω
0.022 µF
49
50 Ω
fr = RF
fr = 10.71 MHz (f2nd osc + 0.45 MHz)
A11778
• IF input
A11779
• Del input
50 Ω
0.022 µF
52
50 Ω
50 Ω
IFT
0.022 µF
45
50 Ω
fr = 450 kHz
fr = 450 kHz
A11780
A11781
No. 6655-47/54
LA1787M
Sample AM tuner Circuit with the LC72144 Used Together
IF
2nd MIX
CF
RF
CF
CF
450K
1st IF
300 Ω
XBUFF
LC72144
fosc
A11782
AM 1st IF
Step
FM IF
1
fOSC 10.25 MHz
10.7 MHz
10 kHz, 11 kHz
10.7 MHz
2
fOSC 10.35 MHz
10.8 MHz
9 kHz, 10 kHz
10.8 MHz
1st MIX
10.71 MHz
CF
RF
IF
CF
10 kΩ
CF
AF
62
59
60
56
53
49
54
1st OSC
52
2nd OSC
31
10.26 MHz
10.7 MHz
RF
63
64
60
59
NC
MPX
Lch
Rch
IF
CF
CF
56
53
Quadrature
detector
AF
51
A11783
No. 6655-48/54
LA1787M
Crystal Oscillator Element
Kinseki, Ltd.
Frequency: 10.26 MHz
CL: 20 pF
Model No.: HC-49/U-S
Coil Specifications
Sumida Electronics, Ltd.
[AM Block]
AM FILTEER (SA-1051)
AM OSC (SA-359)
S
1
2
4
3
3
2
6
1
4
AM IF1 (SA-264)
3
AM IF2 (SA-1063)
4
2
1
6
1
S
S
S
AM loading (SA-1062)
4
6
AM ANT IN (SA-1048)
4
3
2
1
4
3
S 2
3
6
2
6
1
S
6
S
AM RF amplifier (RC875-222J)
0.1ø2UEW
[FM Block]
FM RF (SA-1060)
FM ANT (SA-1061)
S
3
4
2
2
1
4
3
6
1
6
S
FM OSC (SA-1052)
FM MIX (SA-266)
S
3
4
3
C1
4
8
2
2
7
1
6
S
FM DET (SA-208)
S
S
3
4
1
C2
6
S
A136
2
1
6
No. 6655-49/54
LA1787M
The Toko Electric Corporation
[AM Block]
AM FILTEER (A2861BIS-15327)
1
2
3
AM OSC (V666SNS-214BY)
3
4
2
6
4
1
AM IF1 (7PSGTC-5001A)
3
4
1
6 0.05ø3UEW
1
6 0.05ø3UEW
AM ANT IN (385BNS-027Z)
S
4
3
2
1
4
2
AM loading (269ANS-0720Z)
3
AM IF2 (7PSGTC-5002Y)
3
2
6 0.1ø2UEW
4
2
6 0.05ø3UEW
1
6
S
AM RF amplifier (187LY-222)
0.1ø2UEW
[FM Block]
FM RF (V666SNS-208AQ)
S 3
4
2
1
4
2
1
3
4
2
ø0.1–2UEW
6 S
FM OSC (V666SNS-205APZ)
3
FM ANT (V666SNS-209BS)
ø0.12–2UEW
6 S
ø0.1–2UEW
1
6 S
FM MIX (371DH-1108FYH)
S 3
4
2
5
1
6 S
ø0.07–2UEW
FM DET (DM600DEAS-8407GLF)
3
4
2
1
6 0.07ø2MUEW
No. 6655-50/54
LA1787M
Coil Specifications
Sagami Elec Co., Ltd.
[AM Block]
AM FILTEER (000021055)
AM OSC (000021056)
S
1
2
3
3
4
5.1µH
2
6
4
1
AM IF1 (000021057)
3
6
AM IF2 (000021059)
3
4
4
180pF
180pF
2
2
S 1
1
6 S
6
S
AM loading (000021061)
3
4
3
4
100µH
30mH
2
1
AM ANT IN (000021062)
2
6
1
S
6
S
AM RF amplifier (000021063)
2.2mH
[FM Block]
FM RF (000021064)
FM ANT (000021065)
S
3
3
4
105.5nH
2
2
1
4
1
6
6
S
S
FM OSC (000021066)
FM MIX (000021067)
S
3
4
62.7nH
2
1
6
3
4
2
5
1
S
1-2 : 100pF
2-3 : 100pF
6
S
FM DET (010021075)
S 3
4 S
1-3 : 20µH
3-4 : 120pF
2
1
6
No. 6655-51/54
First IF output — dBµ
Mixer output — dBµ
DCV — V
Output, noise, AM output — dB
Output, noise — dB
Total harmonic distortion, THD — %
HCC, SNC, RF AGC, muting voltage,
S-meter voltage, VSM — V
Output, noise, AM output, LR output — dB
LA1787M
Antenna input — dBµ
Mixer input — dBµ
Antenna input — dBµ
Antenna input — dBµ
Antenna input — dBµ
Input — dBµ
Input — dBµ
First IF input — dBµ
No. 6655-52/54
First IF output — dB
First IF output — dB
LA1787M
Frequency, — MHz
Antenna input — dBµ
S/N, AM output — dB
AGC on, separation, input level — dBµ
Frequency, — MHz
Ambient temperature, Ta — °C
Ambient temperature, Ta — °C
AM I/O Characteristics
20
Output, noise — dB
Separation, Sep — dB
0
VCC = 8.5 V
f = 1 MHz
mod = 1 k 30%
OUT
–20
–40
NOISE
–60
–80
–100
–20
0
40
20
Ambient temperature, Ta — °C
3.0
M
VS
1.0
0
20
40
60
80
ANT input, IN — dBµ
100
140
120
140
5.0
4.0
3.0
2.0
z 30%
IF AGC
0
–20
120
fm = 1 kH
4.0
6.0
z 80%
5.0
2.0
100
VCC = 8.5 V
f = 1 MHz
mod = 1 k 30% 80%
fm = 1 kH
AGC, S-meter voltage — V
6.0
Total harmonic distortion, THD — %
7.0
VCC = 8.5 V
f = 1 MHz
RF AGC
80
AM Distortion
AM DC Characteristics
7.0
60
ANT input, IN — dBµ
1.0
0
–20
0
20
40
60
80
100
120
140
ANT input, IN — dBµ
No. 6655-53/54
LA1787M
100 dBμ
desire mod ON
40 dB
μ
60 dBμ
0
80 dBμ
–20
–40
40 dBμ
desire
mod
60 dBμ
OFF
80
μ
dB
μ
100 dB
50/3Ω
–60
–80
40
50Ω
fD=1MHz
fm=1kHz 30%
60
80
30Ω
50Ω 50/3Ω VIN
65pF
fu=1040kHz
JIS
ANT.
DUMMY
fm=400Hz 30%
100
120
140
ANT input, IN — dBμ
Δ400kHz
100 dBμ
desire mod ON
40 d
Bμ
60 dBμ
80 dBμ
–20
40 dBμ
–40
15pF ANT IN
50/3Ω
AM Second-Channel Interference
Rejection Characteristics
–60
–80
40
desire
mod
OFF
80
dB
μ
10
0d
Bμ
Output, noise — dB
0
20
Δ40 kHz
Output, noise — dB
20
AM Second-Channel Interference
Rejection Characteristics
60 dBμ
50/3Ω
fD = 1 MHz
fm = 1 kHz 30%
60
50Ω
80
15pF ANT IN
50/3Ω
30Ω
50Ω 50/3Ω VIN
65pF
fu = 1400 kHz
fm = 400 Hz 30% JIS ANT. DUMMY
100
120
140
ANT input, IN — dBμ
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PS No.6655-54/54