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TDA4504 Datasheet(PDF) 6 Page - NXP Semiconductors |
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TDA4504 Datasheet(HTML) 6 Page - NXP Semiconductors |
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6 / 26 page  February 1992 6 Philips Semiconductors Product specification Small signal combination for multistandard colour TV TDA4504B FUNCTIONAL DESCRIPTION Vision IF amplifier, demodulator and video amplifier Each of the three AC-coupled IF stages permit the omission of DC feedback and possess a control range in excess of 20 dB. The IF amplifier, which is completely symmetrical, is followed by a passive synchronous demodulator providing a regenerated carrier signal. This is limited by a logarithmic limiter circuit prior to its application to the demodulator. A noise clamp circuit is provided at the video input (pin 16) to limit interference pulses below the sync tip level and is more efficient than a noise inverter in providing improved picture stability during the presence of interference. The video amplifier has good linearity and bandwidth figures. AFC-circuit Obtaining the AFC reference signal from the demodulator tuned circuit presents the advantage of utilizing a single tuned circuit and one adjustment. However, since the frequency spectrum of the signal applied to the demodulator is determined by the characteristic of the SAW filter, the resultant asymmetrical spectrum with respect to the vision carrier causes the AFC output voltage to be dependent upon the video signal. The TDA4504B thus contains a sample-and-hold circuit. With negative-going vision signals the AFC is active only during the sync pulse period. When positive-going signals are applied to the device, however, the AFC is continuously active but filtered to ensure only a small by-pass current is present in the sample-and-hold circuit. With weak input signals the drive signal will contain considerable noise which also possesses an asymmetrical frequency spectrum and could create an offset in the AFC output voltage. The inclusion of a notch in the demodulator tuned circuit minimises this effect. The sample-and-hold circuit is followed by a high impedance output amplifier. Thus the AFC control gradient depends upon the load impedance. The AFC polarity switch is combined with the start circuit (pin 12). It has a negative slope when pin 12 is open or connected to the main supply and a positive slope when pin 12 is grounded. The AFC is disabled when the sample connection (pin 22) is grounded. |
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