Example 4 : Determining the cathode resistor for self-bias The value of R k can be computed using the Ohm law by knowing the bias current, that is the cathode current at the operating point (quiescent state), as shown in next Example. Since there is no current flowing through the grid, it is at ground voltage. Rather, a grid leak resistor R l is used to provide the input signal with a high impedance path to ground, as we already discussed for the fixed bias. Note that, also in this case, the grid is not directly connected to ground. The grid, being at ground voltage, is negative with respect to the cathode. Given that, generally, there is an anode current also at the quiescent state, the resistor R k produces a voltage drop from the cathode to ground so that the cathode voltage is above ground. The cathode voltage is elevated by connecting it to ground through the resistor R k, generally called the cathode resistor, as shown in Figure 12. This technique is generally referred as cathode bias or self-bias. Negative voltage between grid and cathode can also be obtained by connecting the grid to ground voltage and by elevating the cathode voltage.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |