This double wide-band AGC system consists of two AGC circuits and a narrow AGC (pin 13 input, mixer input

detection type) as shown in Figure 1. Figure 2 shows the antenna input frequency characteristics.

Figure 2 AGC Sensitivity Detuning Characteristics

Features of the Double Wide AGC System

— Since this is a mixer input detection wide-band AGC, it prevents the occurrence of intermodulation due to

interfering stations with

∆f > 1 MHz. (TV band interference prevention)

— Since this system uses a narrow AGC at the same time, the wide AGC sensitivity can be lowered, thus

preventing incorrect operation due to local oscillator injection.

— Optimal sensitivities for any field conditions can be set, since the sensitivities of both the wide and narrow

AGC systems can be set by changing the values of external components.

— The input level of the desired station is limited by the narrow AGC. As a result, excessive levels are no longer

input to the stages that follow the mixer and the beats at multiples of 10.7

× A are reduced.

• Two-Signal Sensitivity Suppression Characteristics

Previously, keyed AGC systems were used to provide good intermodulation distortion and two signal sensitivity

suppression characteristics at the same time. However, in previous keyed AGC systems, when the desired station

would fade or drop out, the wide band AGC level would become essentially zero. As a result, the automatic station

selection function would malfunction and blocking oscillation would occur in the presence of strong interfering

stations. Thus keyed AGC systems were extremely hard to use in actual practice. Sanyo has developed a new AGC

system (3D-AGC) that solves these problems and allows the construction of extremely simple application circuits.

The LA1193M/V incorporates this AGC system.

What is the 3D-AGC system?

It is a system that determines the wide-band AGC level by using information that has the following three frequency

characteristics.

No. 4715-9/21

LA1193M, 1193V

RF and antenna circuit information

Mixer circuit information

C, F and selectivity information

Mixer input AGC

Mixer output AGC

S-meter output

Three

dimensions