LA3370
Ordering number : EN619H
PLL FM Multiplex Stereo Demodulator
for Car Stereo
Monolithic Linear IC
SANYO Electric Co.,Ltd. Semiconductor Bussiness Headquarters
TOKYO OFFICE Tokyo Bldg., 1-10, 1 Chome, Ueno, Taito-ku, TOKYO, 110 JAPAN
63097HA (KOTO) / 8288YT/3018TA/5205MW, TS No.619-1/11
Overview
The LA3370 is a multiplex IC for FM car stereo, and it has
the following 2 functions through its utilization of the IF
meter output voltage, etc.
1. Stereo noise control (SNC) under which the noise
particular to the FM stereo unit in the weak electric
field is reduced smoothly.
2. High-cut control (HCC) under which the high
frequency is smoothly attenuated. In additioin, the
LA3370 can be, due to its low distortion factor, an IC
for multiplex stereo demodulator which is appropriate
for the car component stereo unit.
Functions
Stereo noise control (SNC terminal)
Through controlling the quality of sound from stereo mode to monaural mode with the voltage applied to the control
pin, the FM stereo noise in the weak electric field is reduced by this function.
High-cut control function (HCC terminal)
The FM noise in the weak electric field is reduced through the attenuation of high frequency thereof.
Such attenuation can be changed smoothly from "Normal" to "High Cut" by controlling the voltage applied to the
control pin. The volume of "High Cut" can be selected by using an external capacitor.
Stereo-monaural automatic select
This selection has priority over the stereo noise control. Pilot input prioritized.
Stoppage of VCO oscillation
When a voltage of 7.5V or higher is applied to the HCC terminal, the oscillation of VCO can be discontinued. In this
case, the stereo lamp does not malfunction.
With separation control terminal.
Features
Low distortion factor. (0.05% typ. 300mV input, mono)
The ripple of power source can effectively be rejected. (35dB typ.)
The range of voltage to be used is wide. (V
CC
=6.5 to 14V)
The space factor is advantageous because of the single-end package.
The printed circuit board can easily be prepared as 3mm pitch is used between the pins.
Package Dimensions
unit: mm
3020A-SIP16
[LA3370]
SANYO: SIP16
LA3370
No.619-2/11
Specifications
Maximum Ratings
at Ta=25C
Parameter
Symbol
Conditions
Ratings
Unit
Maximum supply voltage
VCCmax
16
V
Lamp driving current
IL
40
mA
Allowable power dissipation
Pd max
Ta
45C
520
mW
Operating temperature
Topr
20 to +70
C
Storage temperature
Tstg
40 to +125
C
Recommended Operating Conditions
at Ta=25C
Parameter
Symbol
Conditions
Ratings
Unit
Recommended supply voltage
VCC
6.5 to 14
V
Input signal voltage
VIN
200 to 300
mV
Operation Characteristics
at Ta=25C, V
CC
=10V, V
IN
=300mV, f=1kHz, L+R=90%, pilot=10%
See specified Test Circuit.
Parameter
Symbol
Conditions
Ratings
min
typ
max
Unit
Quiescent current
Icco
21
27
mA
Channel separation
Sep
40
50
dB
Monaural distortion
mono THD
Mono=300mV
0.05
0.2
%
Stereo distortion
ST THD
Main
0.05
0.2
%
Lamp turning-on level
VL
L+R=90%, pilot=10%
60
85
120
mV
Hysteresis
hy
3
6
dB
Capture range
CR
Pilot=30mV
3
%
Output signal level
VO
Sub
140
200
280
mV
S/N ratio
S/N
70
78
dB
Input resistance
ri
20
k
SCA rejection
SCArej
80
dB
Allowable input voltage
VIN
THD=1%
700
800
mV
SNC output attenuation
Att SNC
V8=0.6V, LR=90%, pilot=10%
8.5
3.0
0.3
dB
SNC output voltage
VO sub
V8=0.1V, LR=90%, pilot=10%
5
mV
HCC output attenuation
Att HCC 1
V7=0.6V, L+R=90%, pilot=10%
15.0
6.0
0.5
dB
Att HCC 2
V7=1V, L+R=90%, pilot=10%
2.0
0
dB
Power ripple rejection
Rr
35
dB
VCO stopping voltage
VCO stop
6.8
V
Channel balance
CH Ba
0.5
1.5
dB
Test Circuit
LA3370
No.619-3/11
SNC (stereo noise control) and HCC (high-cut control)
The LA3370 has SNC and HCC terminals for improved S/N ratios when operating in weak radio fields. By adjusting
the SNC terminal, noises unique to stereo FM in weak fields can be reduced. The HCC terminals permits further
improvement of effective S/N ratios by lowering treble levels of FM noises in weak fields. (See Fig.2)
STEREO deteriorates approximately 21.7dB (compared to MONO) in weak radio fields (Fig.2). Generally, when
S/N ratios deteriorate below 30 to 40dB, noises become quite noticeable. Section (1) shows ways to set SNC and
HCC when radio field strengths are divided into 3 regions, A, B, and C (Fig.2). SNC is expected to function in region
A, and HCC in region B. In region C, shallow muting is effected in the IF stage.
Sample Application Circuit and Equivalent Circuit Block Diagram
LA3370
No.619-4/11
(1) SNC (stereo noise control)
Stereo S/N ratios deteriorate 21.7dB below monaural but can be improved by varying stereo separation. S/N
improvement becomes apparent, however, only when the separation is 20dB or worse. In that case, the relation
between separation and S/N improvement is shown in Fig.3.
SNC in the LA3370 improves S/N ratios in weak radio fields by varying separation. It varies subsignal
demodulation level and controls separation. By using the IF stage signal meter level output as the source of the
control signal, S/N ratios in region A of Fig.2 can be maintained at about 40dB or better. Ideal S/N enhancements
should provide gradual switching over from stereo to monaural to maintain constant S/N ratios, starting from a point
in region A for 40dB stereo S/N toward a point for 40dB monaural S/N. Methods to set the control level will be
described later.
Fig.4 shows voltages applied to pin 8 (SNC terminal) of LA3370 versus separation characteristics (SNC
characteristics). Pin 8 is also the base of a PNP transistor, so stereo mode is set when pin 8 is open and monaural
mode is set when it is grounded. SNC terminal control is effective only when locked with pilot signals and when
stereo indicator is lit. External circuit parameters can be chosen in large values that do not affect the IF stage meter
output circuit because SNC control currents are small. This makes designing easy. (See Fig.5)
(2) Designing external circuits for SNC characteristics (characteristic setting by drawing)
We recommend the following as a way to adjust SNC characteristics to have smooth transition of separation from
stereo monaural in region A of Fig.2.
Separation vs. S/N enhancement relation........................... Refer to Fig.3.
SNC pin voltage vs.separation characteristics..................... Refer to Fig.4.
Antenna inputs vs. S/N improvement characteristics can be obtained from the drawing if the graph for IF stage
signal meter output vs. antenna input and the graph for stereo S/N ratio vs. antenna input are known. From desired
S/N characteristics, SNC terminal voltage characteristics can also be obtained. Sample drawings are shown in Fig.6,
where for simplicity's sake, SNC, IF meter, and stereo S/N characteristics have been approximated with straight
lines.
For instance :
To obtain stereo S/N improvement characteristics from SNC characteristics, when (a) in the second quadrant
of the chart represents bare SNC characteristics, point 1 projected to the third quadrant shows a 20dB
separation and a 1dB S/N improvement. When projected from the first to the fourth quadrant, a point
improved by 1dB in S/N over the stereo S/N line in the fourth quadrant corresponds to point 1. Similarly,
point 2 on the SNC characteristics in the second quadrant corresponds to point 2 in the fourth quadrant. Point
3 in the second quadrant corresponds to point 3 in the fourth quadrant. Stereo S/N improvement characteristics
for each point are obtainable. Similarly, (b) characteristics in the second quadrant are projected to form (b)
characteristics in the fourth quadrant, and (c) in the second quadrant to form (c) in the fourth quadrant, thus
providing a way to diagram improvement characteristics.
In the resulting drawings, ideal S/N improvement characteristics are similar to (b) in the fourth quadrant, but
corresponding SNC characteristics have to be (b) characteristics in the second quadrant which are difficult to realize.
Among realistic characteristics, something like (c) appears to be satisfactory. The (c) SNC characteristics are
obtained with a shift by two diodes together with a 1/2 bleeder.
LA3370
No.619-5/11
(3) HCC (high-cut control)
In region B where S/N deteriorates to 40dB or worse even for monaural, the S/N as sensed by the human ear can be
enhanced by suppressing levels at frequencies above approximately 7kHz. Treble region levels that follow meter
voltages can be smoothly attenuated (high-cut control) by impressing IF stage signal meter output to the HCC pin
(pin7) of the LA3370. Fig.7 shows MPX output frequency characteristics (monaural) provided by voltage impressed
on pin 7. Frequency characteristics for a 100% high cut can be determined by an external capacitor connected to pin
4. An equivalent circuit is shown below where the designation is made by the 5k
and the C time constant.
Approximate values provided by C as expressed in attenuation at 10kHz are listed in table below : right.
Fig. 8 shows the relation between voltages impressed on pin 7 and rates (%) of high cut (HCC). When IF meter
output voltage characteristics and region B, S/N characteristics, of Fig. 2 have been obtained, S/N improvement by
HCC can be drawn in a way similar to drawing SNC chracteristics.
Fig.2 shows typical meter outputs of a quadrature detection IF amplifier IC. (Fig. 1 shows data for LA1140) HCC
characteristics have been designated to permit region B improvements when the IC is directly connected to HCC
(pin 7) terminal of the LA3370. The infinitesimal control currents at pin 7, similar to pin 8, do not affect meter
outputs.
(4) SNC and HCC connection circuits when coupled with the IF stage.
Fig. 1 shows sample S/N characteristics via antenna inputs when SNC and HCC are connected with the IF stage by
an external circuit.
(5) S/N improvements in region C of Fig.1
Because S/N ratios deteriorate even further in the region C of Fig. 1, it is better to improve the S/N in this region
with IF mutings. The LA1140 is available to linearly vary the IF muting. Employment of the LA3370 together with
the LA1140 further enhances S/N improvement.
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