Television Receiver Signal Processing and Tuning Systems

Demodulator

Encompasses all techniques used to recover information carried by a carrier wave, which was previously modulated by the transmitter.

Automatic Gain Control (AGC)

This circuit limits the internal intermediate frequency amplifier gain and, if necessary, the input RF amplifier gain when the radio signal is too strong.

Intercarrier System

At the output of the AM demodulator, the composite video signal spectrum contains three distinct areas:

• 0 to 5 MHz: The video signal.
• 4.43 MHz: Chroma information interleaved with luminance.
• 5.5 MHz: Sound carrier with a maximum bandwidth of 150 kHz.

Almost Parallel System

Based on the separation of video and audio signals before demodulation, which is performed independently.

Tuning Control System

A circuit that acts as an interpreter for user commands to manage TV system operating modes accordingly.

I2C Bus

Uses two lines to transmit information: one for data and one for the clock signal. A third line for ground reference is often unnecessary if circuits share the same chassis ground. It consists of two parts:

• Data Line (SDA): Transmits the information.
• Clock Line (SCL): Generates a pulse train to set transmission speed, synchronizing the sender and receiver.

Tuning by Voltage Synthesis

Based on a voltage-controlled oscillator (VCO) using a varactor diode. The varactor's capacity varies with applied reverse voltage. A variation range of approximately 33 volts allows the receiver to tune all channels in UHF bands IV and V. Correct operation requires input voltage for the RF automatic gain control (AGC) and automatic frequency control (AFC).

Tuning by Frequency Synthesis

Based on a Phase-Locked Loop (PLL), consisting of a phase comparator, a VCO, and a low-pass filter. The phase of the input signal is compared with the VCO output signal. The resulting error voltage adjusts the VCO frequency until the input and output signals are phase-locked.