TK14584 Datasheet, PDF (13/20 Pages) TOKO, Inc – FM IF IC

CIRCUIT DESCRIPTION
GND
TK14584
-
+
AMP
VCC
IF Limiter Amplifier, RSSI:
The IF limiter amplifier is composed of five differential gain stages. The total gain of the IF limiter amplifier is 80 dB. The
output signal of the IF limiter amplifier is provided at Pin 10 through the emitter-follower output stage. The IF limiter amplifier
output level is 0.5 V_P-P.
The input resistance of the IF limiter amplifier is 1.8 kΩ (see Figure 1A). If the impedance of the filter is lower than 1.8
kΩ, connect an external resistor between Pin 1 and Pin 2 in parallel to provide the equivalent load impedance of the filter.
Figure 1A shows the case that the impedance of the filter is 330 Ω.
The operating current of the emitter-follower of the IF limiter amplifier output is 200 µA. If the capacitive load is large, the
negative half cycle of the output waveform may be distorted. This distortion can be reduced by connecting an external
resistor between Pin 10 to GND to increase the operating current. The increased operating current from an external resistor
is calculated as follows (see Figure 1B):
The
increased
operating
current
I
e
(mA)
=
(V
CC
-
1.0)
/
R
e
(kΩ)
330
1.8 K
FIGURE 1A
January 2000 TOKO, Inc.
VCC
100 kΩ
IF OUTPUT
Re
Ie
FIGURE 1B
Page 13