Hisense TV, the function and classification of Automatic Gain Control (AGC) circuit There are two main types of AGC circuits: one is the peak AGC circuit; the other is the keyed or synchronous AGC circuit. (1) Peak AGC Circuit A negative polarity sync signal is input to the AGC detector Q2, where it is compared with the reference level Ee. When the sync signal level exceeds the reference level, the total error can be detected by diode D and capacitor C. This error forms an AGC voltage that adjusts the gain of the tuner and IF amplifier. (2) Keyed/Synchronous AGC Circuit This is another method of implementing AGC, which separates the line sync signal from the video signal for detection. Here, the total error detected by diode D is further compared with the line sync signal derived from the line scan pulse via capacitor C1. Technical source: Beijing Hisense TV after-sales service phone http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3764590. The function of the Automatic Gain Control (AGC) circuit is to automatically adjust the gain of the RF and IF amplifiers when the antenna input signal level changes (such as weak signals from distant transmitters; changes in input level caused by the receiving environment, etc.), ensuring a relatively stable video signal for the picture tube in Hisense TVs. The AGC voltage is output from the detector to the tuner, and the RF level is then amplified and detected by the AGC circuit to achieve stable output. This ensures that only stations with sufficiently strong signals are selected to obtain high-quality images.