Signal Processor Descriptions; Tank-Coil-Less Pif Vco; Built-In Sound Band Pass Filter; Aft - TCL 21M62S Service Manual

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Signal Processor Descriptions

1. Tank-Coil-Less PIF VCO

TMPA8873 adopts a tank-coil-less PIF VCO circuit, which has advantages of cost, performance of weak IF
input and easy to design PCB layout. The PIF PLL system has self-alignment circuit, so that the micro
controller needs only to order the PIF PLL system to start self-alignment through the IIC bus. The
self-alignment finishes within 50 ms.

2. Built-In Sound Band Pass Filter

A sound band pass filter is integrated on the chip for multi frequency SIF systems. The 1st SIF demodulator
multiplies PIF input signal and regenerated PIF carrier from VCO with 90° angle, and gets multi-frequency
SIF signal as 6.5 MHz, 6.0 MHz, 5.5 MHz and 4.5 MHz according to the SIF system.
3. Built-In Sound Trap Filter
A sound trap filter is integrated on the chip for multi frequency SIF systems. The sound trap filter
characteristics are changed by WRITE BUS register setting. It is better that the setting data is had for each
SIF frequency.

4. AFT

A recent IF system adopts a digital AFT circuit. But analog DC voltage is used as interface between an IF
system and a micro controller in the AFT control loop. TMPA8873 adopts a digital interface through IIC bus
shown as below.
AFT Window
0
Narrow
AFT Window
0
Wide
AFT Center 1
5. Non-Standard IF Signals
TMPA8873 prepares ways for non-standard IF inputs. The OVER MOD switch is available for
over-modulated PIF signals in the condition of more than 87.5% modulation at 100 IRE, which is the
maximum modulation Standard of PAL and NTSC. In addition, TMPA8873 has capability to modulate more
than 400% over-modulated SIF signal without undesired voltage turning over also.
TMPA8873PSNG /CMNG /CPNG /CRNG /CSNG
1
41.67 kHz
1
41.67 kHz
= 38.0 MHz
f
0
166.68 kHz
41.67 kHz
34
0
41.67 kHz
500.04 kHz
0
41.67 kHz
0
2005/03/29