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            344  Chapter Eight





















                                                      Figure 8.10 A switch for DC
                                                      using a transistor.



























                        Figure 8.11 An RF switch using a diode.


                        Small-signal very high isolation PIN SPDT switch (Fig. 8.12). This switch can be
                        designed with the following formulas, but requires both a forward and a
                        reverse-bias voltage to turn ON and OFF.

                        1. RFC   500 ohms (X ) at f .
                                              L    r
                        2. C   C   1 ohm (X ) at f .
                            B     C           C    r
                               DC bias 	 0.9
                        3. R ≈
                                   50 mA



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