SL1018 Datasheet, PDF (5/9 Pages) AUK corp – FM IF SYSTEM

Information On Muting Characteristics (continued)
Since the pin6 is connected to the base of the emitter ground
transistor through a protection resistor of 500Ω in series as shown
Fig.2. the voltage between pin6 and ground is about 0.7V when
the control current is applied. Actually, the muting operation is
accomplished by applying a muting drive output voltage(pin14) to
the pin6 through a high resistance(20kΩ )
The muting drive output is composed of three output devices:
① Hole Detector output which develops a voltage when C/N
(carrier-to-noise ratio) is lower than weak signal input conditions.
② A reversed output of the signal meter drive output.
③ A bandwidth limited muting drive output which develops a
voltage when the AFC output becomes higher than ±V_BE during
tuning-off operation. All these output are led to an OR circuit and
the output is developed at pin14.
SL1018
I6
6
500
500
- Fig. 2 -
The inverted output of the signal meter drive output is obtained as shown Fig. 3.
Inverter
Inverter
aI2
RL
I1
I1
I1
Inverter
IO
I2
Vr
IL
V cc
IL = IO + I1 - aI2
Io : Offs et
15
Signal
Meter
R15
Output
16
AGC
Output
R16
14
Mu t i n g
De t e c t or
Output
-Fig. 3-
By Fig. 3, V₁₄ is given by V₁₄ = V_r－(I_O + I₁ -al₂)R_L－V_BE. Conditions are V_r=4.9V, I_O ≅ 0.2
mA, a ≅ 2, R_L=22kΩ , V_BE=0.7V, I₁=V₁₅/R₁₅ , I₂=V₁₆/ R₁₆, where V₁₆ is a constant equal to
4.1V(Typ.) for medium or lower signal input levels where the muting drive output is
required. Since the V₁₅ increase proportionally to the increase of the input signal level, I₁
will also increase, and the V₁₄ will decrease. Thus the required muting drive output can be
obtained by selecting proper values of R₁₅ and R₁₆ . Increasing R₁₅ makes the slope of the
curve for the muting drive output vs. antenna signal input decrease, or decreasing the R₁₅
increase the slope of the curve.
KSI-W016-000
5