TK10931VTL データシートの表示（PDF） - Toko America Inc

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TK10931VTL

NARROW BAND FM/AM IF SYSTEM

Toko America Inc  

CIRCUIT DESCRIPTION (CONT.)

Rz is the characteristic impedance

VCC

VCC

VCC

Rz

Rz

Delay

Line

LC Resonance Circuit Ceramic Discriminator

Delay Line

TK10931V

FIGURE 10: EXAMPLES OF PHASE SHIFTERS

(5) AM IF Block

The AM IF block is shown in Figure 11. This block is composed of three blocks: the IF AGC amplifier, the AM IF output,

and the AM detector. The AGC range is approximately 50 dB.

R3

C5

AGC

AMP

VCC DET

AM

IF-OUT

IF-INPUT

C1

C2

C3

R1

R2

AMIF-AGC

AM

DET-OUT

C4

FIGURE 11: AM IF EQUIVALENT CIRCUIT

The AM IF Input Impedance

The AM IF input terminal (Pin 5) is independent of the FM IF input terminal (Pin 7). Respectively different filters for the FM

IF and AM IF can be used. The input impedance of the AM IF input terminal (10kΩ) is higher than the FM IF input terminal

(1.5 kΩ). Although the AM IF input terminal and the FM IF input terminal are conncected in parallel AC wise, when using

common IF filters, it is only necessary to use the FM IF input impedance to determine the termination impedence of the

common IF filter.

AM IF-AGC

Pin 18 is the IF AGC control input terminal. Usually this terminal is connected with the AM detector output terminal (Pin

12) through the ripple filter composed of R1 and C3. The time constant (T = R1 x C3) for the ripple filter is generally selected

to be 5 to 10 times larger than the lowest cycle of the AM modulation element. Pin 18 can also be controlled by an external

DC source instead of the AM detector output signal. Pin 6 is the decoupling capacitor for the AM IF bias circuit.

January 2001 TOKO, Inc.

Page 21

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