la1862m Sanyo Semiconductor Corporation, la1862m Datasheet - Page 14

• Manufacturer Part Number: la1862m
• Description: Single-chip Tuner System For Car Stereo
• Manufacturer: Sanyo Semiconductor Corporation

Detector
1.
2.
3.
4.
5.
IF Count Buffer
1.
2.
3.
4.
SD Output
1.
2.
3.
This IC uses a peak differential detector.
To adjust the detector coil, use the built-in automatic frequency circuit (AFC) and rotate the coil core until the voltage drop
between pins 29 and 33 is 0 V.
Zeroing the AFC and minimizing the total harmonic distortion requires adjusting the capacitance between pin 30 and ground.
Note that stray circuit board capacitance can affect this capacitance value.
The level of demodulation that is output depends on the inductance of the coil between pins 30 and 31, tuning capacity Q
and the capacitor size. Note that although raising Q increases the slope of the S-curve and thus the demodulation output, it
does so at the risk of increasing distortion.
If the destination market is Europe, increasing the slope of the S-curve helps reduce interference from neighboring channels.
Pin 3 is the IF count buffer output. To activate the IF count circuit, apply a 5 V input to pin 3 through a 51 k
The resistor connected to pin 2 determines the IF count buffer output sensitivity (seek stop sensitivity).
Leave pins 2 and 3 open if the IF count buffer is not used.
The largest time constant among those for the following pins determines the transient response characteristic of the IF count
buffer.
Pin 1: the S-meter output, pin 4: the start of muting, pin 5: the muting drive output and pin 29: the AFC output.
IF count system block diagram
To obtain SD output, attach an external NPN transistor to pin 5 as shown in the following figure.
The resistor connected between the base and ground is for
adjusting the SD sensitivity.
The transient response characteristic of the resulting SD
circuit on pin 5 is, like that for the IF count buffer,
determined by the time constants for pins 1, 4, 5 and 29.
Raising the seek speed requires decreasing the time
constants. Decreasing them too far, however, reduces
muting transient response and risks introducing beat noise
and other distortion.
Pin 3 control voltage
The logical AND of the S-meter output and pin 3 control voltage generates the output 10.7 MHz IF count signal.
S-meter output
Band muting
Comparator
LA1862M
Muting drive output
IF count buffer amplifier
IF count buffer output
SD output
SD output
No. 4092- 14/27
resistor.