Pioneer CX-3195 Servis Kılavuzu - Sayfa 7

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1.1.6 Tracking zero-cross amplifier

The tracking zero-cross signal (hereinafter referred to as TEC signal) is obtained by amplifying the TE signal by fourfold,

and used to detect the tracking-error zero-cross point. As the purpose of detecting the zero-cross point, the following two

points can be named:

1. To use for track-counting in the carriage move and track jump modes

2. To use for detecting the direction in which the lens moves in tracking close. (Used in the tracking brake circuit to be

explained later.)

The frequency range of the TEC signal is from 300 Hz to 20 kHz, and

TEC voltage = TE level x 4

The TEC level can be calculated at 4.62 V, which, at this level, exceeds the D range of the operational amplifier, and clips

the signal, but, because the CD LSI only uses the signal at the zero-cross point, it poses no particular problem.

1.1.7 EFM circuit

The EFM circuit converts the RF signal into digital signals of 0 and 1. The AGCO signal output from the pin 119 is

A/C-coupled externally, input to the pin 118, and supplied to the EFM circuit.

Missing RF signal due to scratches and stains on the disc, and asymmetry of the upper and lower parts of the RF, caused

by variation in disc production, cannot be entirely eliminated in AC coupling process, the reference voltage ASY of the

EFM comparator is controlled, using the probability that 0 and 1 occur at 50%. Thus, the comparator level will always stay

around the center of the RFO signal. This reference voltage ASY is generated by passing the EFM comparator output

through the low-pass filter. The EFM signal is output from the pin 113.

PE5547A

RFI

118

Vdd

40k

Fig.1.1.4 EFM

Vdd

7.5k

1.5k

CX-3195

ASY

114

EFM signal

EFM

113