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What aspects should be paid attention to in the chip design scheme of HDMI4K video capture card

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Author : PURPLELEC
Update time : 2023-05-12 10:29:48
  HDMI 4K video capture card chip solution‍The interior of the chip is composed of a large number of transistors. Generally, it is synchronized by the core clock or external clock to operate or control each internal transistor. However, due to the fact that each signal reaches the logic The gate delays are inconsistent, resulting in the state transitions of each transistor not being strictly synchronized. Some transistors may have completed the state transition, while other transistors are still in the process of state transition.
HDMI 4K video capture card
  1. Power supply noise
  The gate circuit that switches to high level inside the chip will transfer the power supply noise to the input ports of other gate circuits. If this part of the gate circuit is in the uncertain state area of level conversion at this time, the power supply noise may be amplified. , and a large rectangular interference pulse is generated at the output end of the gate circuit, which leads to an error in the logic state of the circuit.
  The noise on the external power supply pins of the chip propagates through the internal gate circuits of the chip, and they may cause the state of the internal registers of the chip to change. In addition, the power supply noise will also affect other parts. For example, power supply noise will affect the jitter characteristics of crystal oscillators, phase-locked loops, and DLLs, and the conversion accuracy of ADC circuits.
  2. Decoupling capacitor
  Now, the core clock frequency of the microprocessor and the clock frequency of the peripherals have reached the GHz level, and the level conversion time of the internal transistor has been shortened to the picosecond level. This requires that the power distribution system (PDS) must be able to respond quickly to changes in the load current from DC to GHz, but the existing power regulator chips cannot meet such requirements.
  To this end, it is necessary to add decoupling capacitors to the power pins of the chip. When the transient current of the load changes, due to the fast switching speed of the transistor level state inside the load chip, it is necessary to supply enough current to the load chip in a very short time, but the regulated power supply cannot respond so quickly changes in load current.
  See if it supports all common formats and common resolutions, and also supports 4K resolution output. After stretching and compressing fixed-ratio video sources, it still has high-quality video display effects, and all videos can share audio input and output. , the audio input from any channel can be output to any audio output channel.
  The choice of capacitor combination in the HDMI 4K video capture card chip solution needs to be specially designed according to the specific application, such as capacitor packaging, material, capacitance, capacitance step value, main clock frequency and its harmonic frequencies, Factors such as signal rise/fall times. Although the more capacitance levels you choose, the flatter the impedance characteristics will be, but it is not necessary to use capacitors with a variety of capacitance values. Because the goal is that the total impedance is less than the target impedance, as long as this requirement can be met.