Figure 4-6 is a block diagram of a color TV set, mainly including 6 parts of high-frequency tuner, mid-range amplifier and detection, audio channel, PAL decoder, synchronization and scanning, remote control system. ?
1. High frequency tuner?
The high-frequency tuner is also called a high-frequency tuner. It has the functions of selecting channels, amplifying signals, and changing frequencies. The function of the antenna and the input circuit is to select the weak TV signal of the desired channel, which is selectively amplified by a high-frequency amplifier, and then mixed with a sine wave with a higher frequency output by the local oscillator to obtain an intermediate frequency signal. The high-frequency tuner has good selectivity and can suppress image (intermediate frequency 2 times higher than the signal frequency) interference, intermediate frequency interference and other interference signals. The coupling between the isolation mixer and the antenna can avoid the local oscillator signal radiating out through the antenna and disturbing other receivers.
The mixer converts the received radio frequency television signals of different channels into fixed frequency intermediate frequency signals. China stipulates that the image intermediate frequency is 38 MHz, and the first sound intermediate frequency is 31.5 MHz. The latter intermediate frequency amplifier can obtain good selectivity and higher gain due to the fixed frequency. The total gain of a general high-frequency tuner is about 20 dB. ?
2. CLP and detection?
The intermediate frequency amplifier amplifies the image intermediate frequency signal and the first sound intermediate frequency signal sent by the high frequency tuner. Its main task is to amplify the image intermediate frequency signal. The amplification factor of the sound intermediate frequency signal is very small, so the intermediate frequency amplifier is often referred to as the image. put. The intermediate amplifier is the main amplifying unit of the entire TV receiver, and the gain is required to be above 60 dB. ? In order to adapt to the residual sideband transmission and suppress interference, the characteristic curve of the intermediate discharge is of special shape, which is formed by the SAWF filter once. ?
The first task of the video detector is to detect the video image signal from the intermediate frequency image signal. Generally, the large signal detection is envelope detection. The second task of the video detector is to use the non-linearity of the diode to generate a 6.5 MHz second sound IF signal from the image IF and sound IF beats. ?
The output signal of the detector should be provided to the PAL encoder, synchronous separation circuit, automatic gain control (AGC) circuit and audio amplifier circuit, so the video pre-amplification is carried out to enhance its load capacity. The pre-amplification from the antenna to the video is called the common channel (picture and sound). ?
The function of the automatic noise suppression (ANC) circuit is to automatically suppress interference pulses, so as not to affect the normal operation of the synchronous separation circuit. A common method is to separate out the interference pulses, and then superimpose them on the original signal after inverting the phase, thereby canceling the interference pulses. ? The function of the automatic gain control (AGC) circuit is to detect a DC voltage that changes with the level of the input signal to control the gain of the intermediate frequency amplifier and the high frequency amplifier to keep the output amplitude of the video detection basically unchanged. ?
3. Sound channel?
The 6.5 MHz second sound IF signal taken from the video pre-amplifier is sent to the sound IF amplifier, after amplification and limiting, it is sent to the discriminator for frequency detection, the audio signal is detected, and then the low-frequency amplifier is finally obtained at the speaker TV soundtrack.
4. PAL decoder?
For details of the PAL decoder, see the PAL decoder in Section 3.3.6 and the block diagram of the PAL decoder shown in Figure 3-21.
5. Synchronization and scanning circuit?
The video image signal is sent to the synchronization separation circuit after the interference pulse is eliminated by the ANC circuit, and the composite synchronization signal is separated. After the composite synchronization signal is amplified, the field synchronization signal is separated by the integration circuit, and then the field synchronization signal is used to control the sawtooth wave signal generated by the field oscillator to be synchronized with the transmitting end. The field scanning current is generated. ?
In order to improve the anti-interference of the line scan circuit, modern television receivers all use automatic frequency phase control (AFPC) circuit. The composite synchronization signal is directly added to the phase discriminator of the AFPC circuit and compared with the horizontal oscillation signal. If there is a difference in frequency and phase between the two, a voltage proportional to the error is output to control the frequency and phase of the horizontal oscillator to synchronize with the origin. Due to the role of the low-pass filter in the AFPC circuit, the anti-interference of the horizontal synchronization is enhanced.
The horizontal oscillating signal synchronized with the transmitting end is amplified by the horizontal driving stage and the horizontal output stage, and a horizontal deflection current is generated in the horizontal deflection coil. The line scan reverse pulse is boosted and rectified to obtain the high voltage, medium voltage and the voltage required by the video amplifier circuit (combined with the PAL decoder primary color matrix). The auxiliary circuits of the color picture tube include convergence, geometric distortion correction, white balance adjustment, color purity adjustment, demagnetization and other circuits. ??
Welcome to reprint, this article comes from the electronic enthusiast network (http: //)
6. Remote control system?
The remote control system is composed of the local keyboard, program memory, infrared remote control transmitter, infrared receiver, microcontroller and interface circuit. ?
The local keyboard is located on the TV panel. The user can operate the local keyboard to complete the selection, preset or various functions of the TV. ?
The function of the keyboard on the infrared remote control transmitter is basically similar to the local keyboard. The difference is that it can be far away from the TV and control the TV through the infrared light command signal. When a key of the infrared remote control is pressed, the encoder in the remote control outputs a set of corresponding binary codes, which are modulated on a 38 kHz carrier wave, and then the infrared light emitting diode is modulated to become an infrared remote control command signal. After the infrared photodiode installed in the infrared receiver behind the TV panel receives the infrared remote control command signal, the binary code of the command is obtained through amplification, detection and shaping, and then sent to the microcontroller for decoding to identify the type of control and Content, send corresponding signals accordingly, and adjust the TV through the interface circuit.
The program memory uses electrically erasable programmable read-only memory (EEPROM), which is used to store the tuning voltage data of several channels, various function control parameters, etc., and also store the last TV program information, including channel number, TV / AV status, Volume, brightness, contrast, color saturation, etc. ?
The microcontroller is the core of the remote control system. It is controlled by 8-bit arithmetic and logic operators, various registers, voltage or frequency synthesizers, RAM (data memory), ROM (solidify all channel selection, presets and various functions) Program), I / O port, instruction decoder, bus, master clock, etc. Work with the peripheral circuit to execute the user's remote control commands, such as channel selection, preset, volume, brightness and other functions. ?
The interface circuit converts various function control instruction codes sent by the microcontroller into 64-level analog control voltage after decoding and D / A conversion, and then controls the volume, brightness, color saturation, power supply, etc. ?
BLPS laser safety protective device is designed for personal safety used on hydraulic bender.
The dynamic test technology it used has passed the Type 4 functional safety assessment by TUV, and get the national invention patent. The product reaches the advanced technological level of similar products.
BLPS laser safety device provides protection zone near the die tip of the bender to protect fingers and arms of the operator in close to the upper mold die tip. It is the most effective solution so far to preserves the safety and productivity of the bender.
Press Brake Protection,Laser Safety Guard Device,Laser Guarding Device,Press Brake Laser Guard,Press Brake Guarding Systems,Press Brake Guarding
Jining KeLi Photoelectronic Industrial Co.,Ltd , https://www.sdkelien.com