Toshiba TW40F80 SECTION II TUNER, IF/MTS/S. PRO MODULE 1. CIRCUIT BLOCK, Outline, Major Features

SECTION II: TUNER, IF/MTS/S. PRO MODULE

1. CIRCUIT BLOCK

EL466L

Tuner

RF AGC

IF/MTS/S.PRO Module MVUS34S
		SIF
SAW	VIF/SIF	output	Sound
			Multiplex		S.PRO Circuit
Filter	Circuit
			Circuit
					C-IN
					R-IN L-IN
	TP12		TV	TV
	Video output		R-OUT	L-OUT
					R-OUT		C-OUT
AFT output	To A/V switch circuit					L-OUT	(L+R)
							-OUT

Fig. 2-1 Block diagram

1-1. Outline

(1)RF signals sent from an antenna are converted into in- termediate frequency band signals (video: 45.75 MHz, audio: 41.25 MHz) in the tuner. (Hereafter, these sig- nals are called IF signals.)

(2)The IF signals are band-limited in passing through a SAW filter.

(3)The IF signals band-limited are detected in the VIF circuit to develop video and AFT signals.

(4)The band-limited IF signals are detected in the SIF cir- cuit and the detected output is demodulated by the au- dio multiplexer, developing R and L channel outputs. These outputs are fed to the A/V switch circuit.

(5)A sound processor (S.PRO.) is provided.

(5)VIF/SIF circuit uses PLL sync detection system to improve performances shown below:

•Telop buzz in video over modulation

•DP, DG characteristics (video high-fidelity repro- duction)

•Cross color characteristic (coloring phenomenon at color less high frequency signal objects)

(6)HIC SBX1637A-22 is used in the audio multiplexer circuit to minimize the size with increased performance.

(7)As a sound control processor, TA1217N is used. I2C- bus data control the DAC inside the IC to perform switching of the audio multiplexer modes.

1-2. Major Features

(1)The VIF/SIF circuit is fabricated into a small module by using chip parts considerably.

(2)As the tuner, EL466L that which contains an integrated PLL circuit is employed.

(3)Wide band double SAW filter F1802R used.

(4)FS (frequency synthesizer) type channel selection sys- tem employed.

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