[Multinetwork PLL]

The multinetwork PLL consists of the blocks shown below.

The multinetwork PLL has two VCO circuits. Each of these form a separate PLL. The operational relationship between these

circuits is as follows:

Initially, in APC1, the phases of the IF signal and the VCO carrier are compared. The control signal derived is then used to

control VCO2. VCO1 is controlled by comparing the phases of VCO2 and VCO1 x 1/8. As a result, VCO1 always has the same

frequency as the IF signal, and the following relationship results:

phase error is very small. As a result, the multinetwork PLL operates as an ideal PLL detector.

Automatic Quadrature Tuning (AQT)

A quadrature detector that is controlled automatically is used in the FM detector. The AQT in the LA7583 consists of the blocks

shown in the following diagram.

The FM detection filter (gyrator) is controlled at 4.5 MHz by the control current (Iref1) generated by reference circuit 1. At the

same time, precision control is performed by using the control current (Iref2) derived by detecting the offset from the detected

output so that the FM detector phase relationship is 90 °. As a result, automatic control makes an ideal quadrature detector

possible.

(Note) Gyrator: Circuit-formed equivalent inductance

The SIF circuit contains a 4.5 MHz tank circuit having the gyrator and an internal capacitor.

LA7583

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