AVE ppt on TV receiver (PAL - D circiut main)

2. Pooja

4. 5 different stages

5. Stage 1(Q1) and 2(Q2 and Q3), colour saturation, colour killer bias and burst blanking pulse stage.

8. o/p pal d = V and U ( scaled down colour difference signals U=0.493(B-Y) and V=0.877(R-Y)

9. o/p y channel = luminance (brightness)signal (y)

12. Encoding= process of combining the 2 colour difference signals by translating them to a higher freq. domain.

13. Since the 2 carrier freq. are suppressed in the balanced mod. of the encoder, it is necessary to regenerate them at the receiver for demod. of the chroma signal.

17. Stage 1 (Q1) Input to Q1 via C1 Gain controlled by XL1 Magnitude of ACC voltage fed to base Q1 via R1 R2 C2 avoids undesirable feedback between Q1 and ACC. Ie of Q1 = 0.5Vpp o/p to stage 2 via C6 o/p to burst stage via C5 Function of ACC amp. = o/p Voltage used to control gain of 1st stage of chroma amp. for constant chroma signal amplitude.

19. Stage 2 (Q2 and Q3) Consists of transistors Q2 and Q3 Q2 acts as emitter follower Q3 acts as phase splitting amplifier i.e. to provide anti-phase chroma signal for chroma delay line circuit that separates U and V signals.

21. Colour saturation control section Saturation Determines the pureness of the colour. Level of saturation indicates amounts of other colours present in received light. Saturation control section - function is as a variable attenuator to change mag. of the chroma signal led to U and V demodulator. Consists of D1,D2 with R7,R9.

23. Burst pulse blanking D3,D4 and R18 prevent the colour burst pulses from getting through the second stage. Blanking level > to avoid visibility during fly back time.

25. Colour killer control Function – rectifies burst pulses to produce steady dc V. and keeps the 2nd stage amp operative allowing the chroma signal to reach the demodulators. In case B&W, no burst pulses, no dc V, and 2nd amp blocked, no colour.

28. Thank you !