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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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TDA4655 датащи(PDF) 5 Page - NXP Semiconductors |
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TDA4655 датащи(HTML) 5 Page - NXP Semiconductors |
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5 / 17 page  June 1993 5 Philips Semiconductors Preliminary specification Generic multi-standard decoder TDA4655 FUNCTIONAL DESCRIPTION The IC contains all functions required for the identification and demodulation of signals with the standards PAL, SECAM, NTSC 3.5 with 3.58 MHz colour-carrier frequency and NTSC 4.3 with 4.43 MHz colour-carrier frequency. When an unknown signal is fed into the input, the circuit has to detect the standard of the signal, and has to switch on successively the appropriate input filter, crystal (8.8 or 7.2 MHz) and demodulator and finally, after having identified the signal, it has to switch on the colour and, in event of NTSC reception, the hue control. At the outputs the two colour difference signals −(R−Y)* and -(B −Y)* are available. The identification circuit is able to discriminate between NTSC signals with colour-carrier frequencies of 3.58 MHz or 4.43 MHz. ACC-stage The chrominance signal is fed into the asymmetrical input (pin 11) of the ACC-stage (Automatic Colour Control). The input has to be AC coupled and has an input impedance of 20 k Ω in parallel with 10 pF. To control the chrominance amplitude the modulation independent burst amplitude is measured during the burstkey pulse which is derived from the sandcastle pulse present at pin 24. The generated error current is fed into an external storage capacitor at pin 12. The integrated error voltage controls the gain of the ACC stage so that its output is independent of input signal variations. The measurement is disabled during the vertical blanking to avoid failures because of missing burst signals. Reference signal generation The reference signal generation is achieved by a PLL system. The reference oscillator operates at twice the colour-carrier frequency and is locked on the burst of the chrominance signal (chr). A divider provides reference signals (fSC) with the correct phase relationship for the PAL/NTSC demodulator and the identification part. In the SECAM mode the two f0 frequencies are derived from the PAL crystal frequency by special dividers. In this mode the oscillator is not locked to the input signal. In the NTSC mode the hue control circuit is switched between ACC stage and PLL. The phase shift of the signal can be controlled by a DC voltage at pin 13. The hue control circuit is switched off during scanning. The reference frequency (2 × fSC) is available at pin 19 to drive a PAL comb filter for example. Demodulation The demodulation of the colour signal requires two demodulators. One is common for PAL and NTSC signals, the other is for SECAM signals. The PAL/NTSC demodulator consists of two synchronized demodulators, one for the (B −Y) Channel and the other for the (R −Y) Channel. The required reference signals (fSC) are input from the reference oscillator. In NTSC mode the PAL switch is disabled. The SECAM demodulator consists of a PLL system. During vertical blanking the PLL oscillator is tuned to the f0 frequencies to provide a fixed black level at the demodulator output. During demodulation the control voltages are stored in the external capacitors at pins 4 and 10. The oscillator requires an external resistor at pin 7. Behind the PLL demodulator the signal is fed into the de-emphasis network which consists of two internal resistors (2.8 k Ω and 5.6 k Ω) and an external capacitor connected at pin 2 (220 pF). After demodulation the signal is filtered and then fed into the next stage. Blanking, colour-killer, buffers As a result of using only one demodulator in SECAM mode the demodulated signal has to be split up in the (B −Y) Channel and the (R−Y) Channel. The unwanted signals occuring every second line, (R −Y) in the (B −Y) Channel and (B−Y) and in the (R −Y) Channel, have to be blanked. This happens in the blanking stage by an artificial black level being inserted alternately every second line. To avoid disturbances during line and field flyback these parts of the colour differential signals are blanked in all modes. When no signal has been identified, the colour is switched off (signals are blanked) by the colour killer. At the end of the colour channels are low-ohmic buffers (emitter followers). The CD output signals −(B−Y)* and −(R−Y)* are available at pins 1 and 3. Identification and system control The identification part contains three identification demodulators. The first demodulates in PAL mode. It is only active during the burstkey pulse. The reference signal (fSC) has the (R −Y) phase. The second demodulator (PLL system) operates in SECAM mode and is active also during the burstkey pulse, but delayed by 2 µs. The PLL demodulator discriminates the frequency difference between the unmodulated f0 frequencies of the incoming signal (chr) and the reference frequency input from the crystal oscillator. These two demodulators are followed by an H/2 switch ‘rectifying’ the |
Аналогичный номер детали - TDA4655 |
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Аналогичное описание - TDA4655 |
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