Pioneer SX-6 Panduan Servis - Halaman 9

Jelajahi secara online atau unduh pdf Panduan Servis untuk Penerima Pioneer SX-6. Pioneer SX-6 15 halaman. Computer controlled stereo receiver
Juga untuk Pioneer SX-6: Panduan Servis (25 halaman)

Halaman Cetak

Tuner Stage

O I.D. MOS FET

The FM front-end RF amplifier in model SX-?

(and SX-6) features an I.D. MOS FET (ion-implan-

tation dual gate MOS FET) - P001 manufactured

by Pioneer Semiconductor Laboratory. The major

features of this FET - P001 include high gain,Iow

noise, Iow distortion and low IM (P.G. 25dB/

100MHz, N.F. 2dBl100MH2, I.M. -54d8/107dBp)

as a result of an extremely accurate short channel

obtained by a "self aligning" operation involving

a "local silicon oxidation" process. Furthermore,

a O.4p narrow channel (1/3rd to 1/5th the width

in normal components) has been achieved by the

ion-implantation double diffusion construction.

Use of this FET in the FM front-end greatly

assists in improving sensitivity and reducing inter-

ference.

o Pulse-Swallow

PLL Synthesizer

When the VCO (Voltage Controlled Oscillator)

frequency is very high and the CMOS progmmm-

able divider operating frequency is exceeded, the

PLL will cease to function. Two methods are

presently available to resolve this problem. In one

of these methods (the fixed divider system), an

ECL (Emitter to Emitter Coupled Logic) prescaler

is positioned in front of the programmable divider.

And when, for example, a 1/10 prescaler is em-

ployed to obtain

25kHz step frequencies, the

reference frequency will be 2.5kHz. This frequency

is very low and cannot be adequately removed by

the low-pass filter. As a result, signal components

are leaked into the mixer leading to deterioration

in the S/N ratio. This is one of the main dis-

advantages of the fixed divider system.

The other method available is the pulse-swallow

system which employs a special frequency divider

called a "two-modulus prescaler" instead of the

prescaler used in the fixed divider system. In this

method, a 25kHz step synthesizer will generate a

25kHz reference frequency and a 50kHz step

synthesizer

will

generate a 50kHz

reference

frequency, resulting in a much higher S/N ratio

than in the fixed prescaler system.

The pulse-swallow system employed in the SX-7

is incorporated in an IC (M54922P) controlled by

microcomputer.

Amplifier Stage

o Non-Switching

Amplifier (SX-7, SX-6, SX-s)

In non-switching amplifiers, the output stage

transistor bias is controlled on the basis of class B

operating point in order to maintain the operation

within the operating region (between cutoff and

saturation) and thereby suppress the generation of

switching distortion.

The basic non-switching amplifier circuitry is

outlined in Fig. 1-2. To simplify the diagram,

transistor Vgn

and diode Vg, E1 and E2 are

assumed to be 0.6V and the transistor base current

is disregarded. While no input signal is applied, the

voltage drop across R5 and R6 may also be dis-

regarded. And if the voltage across R1 and R2 due

to idle current is ignored, the voltages at different

positions will be as shown in the diagram.

When an input signal is applied, a voltage will be

generated across Rt by NPN stage (Q1/Q3) oper-

ation during the positive portion of the signal. This

voltage is applied to the Q5 emitter-follower

(voltage gain of about 1) resulting in almost the

same voltage being generated across Rb. This

voltage is then added to the output stage bias

voltage. Hence, the PNP stage (Q2/Q4) maintains

the same bias conditions as when no signal was

applied, which means there is no cutoff. Likewise,

the NPN stage maintains the same bias conditions

during the negative portion of the signal as when

no signal was applied, again eliminating any cutoff.

F i s . 1 - 1

Pulse swallow system

Fig. 1-2

Basic circuitry of Non Switching Amplifier