LA1260
No.1506-5/14
AM oscillation coil
Generally speaking, the following should be noted. Winding with loose
coupling between 1 and 2 and between 1 and 3 must be avoided. (Particularly
SW1, SW2).
To put in concretely, the pot core type is better than the screw core type which
is loose in coupling. This prevents the local oscillation frequency from turning
third resonance frequency related to the coupling coefficient.
LED unlighted time and distortion in AM (MW)
By increasing the value of the electrolytic capacitor for AGC at pin 11 (Figure 8), the distortion in the AM mode can
be improved, but the LED unlighted time is made longer. 10μF is recommended for obtaining the optimum LED
unlighted time and distortion. The LED unlighted time is 200ms at this value (Approximately 400ms at 22μF).
FM-AM selection and dc level at pin 12
(1) Pin 12-used method=recommended circuit
The FM mode is entered with pin 12 open. When pin 12 and pin 6
are at the same potential in terms of DC, the AM circuit is turned on
by the internal switch. It should be noted that the dynamic range is
narrowed whether the potential at pin 12 is lower or high than that
at pin 6.
(2) Pin 13-used method
The AM mode is entered with pin 13 open. When pin 13 is
grounded, the FM circuit is turned on and the AM circuit is turned
off by the internal switch. In this case, pin 12 and pin 6 (VCC) are
at the same potential.
Unit (capacitance : F)
Receiving frequency, fr – Hz
OSC
voltage
at
coil
end,
V
OSC
–
mV
V16
OSC
voltage
–
mV
Figure 7
MW OSC characteristic
Modulation degree – %
Total
harmonic
distortion,
THD
–
%
Figure 8
Input 100dBm
VCC=4.5V
AM mod. char. and electrolytic
capacitor at pin 11.
100Hz,
capacitor
across
pin
11
and
Gnd
: 10
μF
V16
OSC
voltage
OSC
voltage
at
coil
end
Relation between turn
ration n and OSC level
Unit (capacitance : F)