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| 型号： | TK14489V |
| 厂商： | TOKO INC |
| 元件分类： | 接收器 |
| 英文描述： | FM, AUDIO SINGLE CHIP RECEIVER, PDSO20 |
| 封装： | TSSOP-20 |
| 文件页数： | 11/25页 |
| 文件大小： | 2570K |
| 代理商： | TK14489V |
TK14489V
GC3-E011E
Page 19
12. APPLICATIONS INFORMATION
12-1. Operations Account
RF signal, which is inputted into pin 20, and local
oscillator signal from local oscillator are mixed in
multiplier. Mixer output, which is frequency-converted
RF signal as IF signal, is outputted to pin 4. Mixer output
is inputted into pin 6, which is IF limitter amplifier input
pin, through external narrow band width BPF. IF signal,
which is limiting amplitude in IF limitter amplifier, is
phase-shifted by pin 10. After quadrature-detected, IF
signal is outputted from pin 11 pin as AF output signal.
RSSI signal is outputted to pin 12 pin. IF signal diverged
from IF limitter amplifier is converted current that is
suitable for input level by demodulator. After that,
converted signal is outputted from pin 12.
Noise level, which increase being inverse proportion to
signal level, is inputted squelch rectified through an
active filter which center frequency is established over
the AF.
An inverting amplifier, which has input terminal of pin 13
pin and output terminal of pin 14, and impedance circuits
are constituted an active filter. A rectifier is structured on
external parts.
Output from rectifier, which is controlled as noise level,
is injected into pin 15. Pin 16 is GND level and pin 17 is
"off" mode when the voltage adding in pin 15 is 0.7V or
more. Pin 16 is Hi level and Pin 17 is " on " mode when
the voltage adding in Pin pin is less than 0.7V . Normally,
pin 18 is connected with GND by resistor. Squelch input
has hysteresis to obstruct input jitter. Hysteresis width is
variable by changing value of hysteresis resistor.
12-2. Mixer Section
12-2-1. Mixer
Mixer consists of Gilbert cell and a local oscillator.
Mixer realizes wide dynamic range with high conversion
gain, 31dB when output terminal is open.
RF input is unbalanced input.
12-2-2. Local Oscillator
Figure 3: Examples of Oscillator
i) X'tal Oscillation
ii) LC Oscillation
Vcc
1
2
Vcc
1
2
Oscillator includes normal common collector Colpitts
oscillator. Its operating current is about 100A.
It is indicated examples of oscillator circuits in fig. 3.
We explain the examples since next paragraph.
(1)A case of using external SSG or oscillator
It showed circuit composition in fig. 4, using external
oscillator. In the case of not using an inner oscillator but
use an external oscillator, local level must be injected into
pin 1 by capacitor cappling.
In that case, pin 2 must be opened.
The local oscillator operates as only an emitter
follower by opening pin 2 and injecting into pin 1.
Figure 4: External Injection
~
Vcc
1
2
open
50
50
0.01
RF
IF
(2)A case of the 3rd overtone oscillation
In general, crystal oscillator can oscillate fundamental
oscillation and overtone oscillation. For example, it is
easy for 30MHz overtone oscillator to oscillate 10MHz,
fundamental oscillation. The reason is why the impedance
of fundamental oscillation is little as same as the
impedance of overtone. It is necessary for circuit side to
choice overtone frequency using a tuning-coil and so on,
to get overtone oscillation.
We explain how to oscillate normal 3
rd overtone oscillator.
In the case of overtone oscillation of 30MHz or more,
using a crystal oscillator, we recommend a circuit in fig. 5
to suppress fundamental-wave-mode-oscillation.
Figure 5: Overtone X'tal Oscillator
Vcc
1
2
X'tal
C
1
C
3
L
C
2
R
e
We explain how to decide circuit constant of overtone-
crystal-oscillation fundamental circuit. It happens to drop
oscillation intensity when it is short of g
m of oscillator, as
operation frequency grows high. It is easy to increase
operation current connecting resistor R
e between pin 2
and GND. It makes g
m increase to increase operation
current by connecting external resistor R
e, if it is short of
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