What Is Circuit Restoration?
The clamp circuit is a circuit that fixes a certain part of the pulse signal waveform to a selected level, and keeps the waveform shape of the rest of the original signal unchanged. The clamping circuit can restore the DC component of the pulse signal that has lost the DC component, so it is also called DC restorer.
- The clamp circuit is also called a DC component recovery circuit, which is used to recover the DC component that has been lost in the image signal.
- There are two types of clamping circuits: simple unidirectional clamping and forced bidirectional clamping. The simple one-way clamping circuit uses the switching action of the diode to instantaneously clamp to a fixed potential whenever a blanking or synchronization pulse arrives. The disadvantage of this circuit is that when the amplitude of these pulses suddenly decreases, the clamping effect will be lost; and when a larger interference pulse arrives, the peak value of the interference pulse will be clamped, which will cause the subsequent lines to lose clamping. The forced bidirectional clamping circuit is a clamping circuit controlled by a keying pulse. When a keying pulse arrives, it is forced to clamp to a fixed level regardless of the level of the bit signal. Other times, no clamping occurs Bit effect. This overcomes the two disadvantages mentioned above. [1]
- The clamp circuit is commonly used in various display devices. in
- Figure 1 is a diode clamping circuit. In the figure, the resistance R is much larger than the on-resistance R D of the diode D. Assumption: The input signal u i is a series of rectangular pulses starting at time t = 0 (Figure 2). The product R C of the resistor R and the capacitance C is much larger than the interval time of the input pulse T 2. The capacitor C is charged before t = 0. Done. The level of the output signal u 0 is E C. Therefore, at t = 0, the first positive pulse is input, and the diode is turned on. If the charging time constant 1 = R D C < T 1/3, the capacitor is quickly charged and the output signal is clamped at the E C level. The diode is reverse biased and turned off during the pulse interval t 1 to t 2, and its resistance value is greater than R. Because the discharge time constant 2 = R C >> T 2, the voltage on the capacitor C changes little, and the output signal follows the input signal. Similarly, when the second positive input pulse arrives, the diode is turned on again, the capacitor is quickly charged, and the output signal is quickly restored to the EC level. The operation of the circuit during t 3 to t 4 is the same as that during t 1 to t 2. After that, the circuit operation of each cycle is completely the same as that of the second cycle (ie, t 2 ~ t 4). According to FIG. 2, the waveform of the output signal after t 2 is basically the same as the input signal, except that its top is clamped at the EC level. The circuit in Figure 2 uses the difference between the charging time constant 1 and the discharging time constant 2 to form a voltage on the capacitor that can automatically adjust and maintain a constant voltage for a certain time interval to achieve clamping work. Changing the size of the power supply E C can change the value of the clamping level; reversely connecting the diodes can implement a circuit with the bottom level clamped. The clamping circuit of the waveform in Figure 2 can only cause the clamping action to occur at the top or bottom of the pulse. If you want to clamp a certain intermediate level of the input waveform, you can use a clamp circuit with a control pulse.
- Clamp circuit