µPC1830

13

5. BLOCK OPERATION

5.1 Video Signal Processing Section

(1) Input signal

After coupling by a capacitor (0.22

pin (pin 36).

(2) Clamp circuit

The clamp circuit controls the pedestal voltage level to be constant to make it a reference voltage for the post-stage

signal processing.

(3) Chroma trap circuit

Eliminates the chroma signal (NTSC system: approximately 3.58 MHz, PAL system: approximately 4.43 MHz) from

a composite video signal and extracts a brightness signal.

(4) Separate/composite switching circuit

Operates as shown in Table 5-1 according to the voltage of the separate chroma input pin (pin 34).

Table 5-1. Operation when Switching Separate/Composite Signals

Separate chroma input

Mode

Brightness signal

ACC amp input

pin (pin 34) voltage

processing

Less than 3.7 V

Y/C separate input

Without chroma trap

Input from separate chroma

3.7 V or higher

Composite video input

With chroma trap

Input from chroma BPF

(5) Delay circuit

Compensates for the delay between the brightness signal and chroma signal by delaying the brightness signal.

(6) Contrast adjustment circuit

Adjusts the amplitude of the brightness signal output from the Y output pin (pin 12) according to the voltage of the

contrast control pin (pin 38).

The control characteristic is shown in Figure 5-1.