GENERAL DESCRIPTION
The TDA4570 is an integrated 3,58 MHz or 4,43 MHz NTSC decoder. It is pin sequence compatible with multi-standard decoder TDA4555 and pin compatible with the PAL decoder TDA4510.

FEATUREs
Chrominance part
• Gain controlled amplifier with operating point control stage
• ACC (automatic chrominance control) with sampled rectification during burst-key signal
• Blanking circuit for the colour burst signal

Oscillator and control voltage part
• Voltage controlled reference oscillator for double subcarrier frequency
• Divider stages which provide the correct 90° phase between −(R-Y) and −(B-Y) reference signals for the demodulators
• Phase comparator which controls the frequency and phase of the reference oscillator and compares the (R-Y) reference with the burst pulse
• HUE control stage provides phase shifting via the combined service and hue control input (pin 11)
• Identification demodulator provides a positive-going identification signal at pin 14 for NTSC signals and acts as the automatic colour killer
• Two-function service switch:
    – position one (V14-3 < 1 V): switches the colour-ON and switches the hue control and burst for the PLL oscillator-OFF, allowing the adjustment of the reference oscillator
    – position two (V14-3 > 5 V): switches the colour-ON, the hue control OFF and allows the output signal to be observed
• Sandcastle pulse detector for burst-gate, horizontal and horizontal/vertical blanking pulse detection. The vertical part of the sandcastle pulse is used for the internal colour-ON and colour-OFF delay
• Pulse processing part for the prevention of premature switching ON of the colour. The colour-ON delay, two or three field periods after identification of the NTSC signal, is achieved by a counter. When there is no identification voltage present the colour is switched OFF immediately or, at the most, one field period later.

Demodulator part
• Two synchronous demodulators for the (R-Y) and (B-Y) signals, which incorporate stages for the blanking during line and field flyback
• Internal filtering of the residual carrier in the demodulated colour difference signals
• Colour switching stages controlled by the pulse processing part in front of the output stages
• The output stages for (R-Y) and (B-Y) signals are low resistance n-p-n emitter followers
• Separate colour switching output