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→The Gain Switch
==== The Gain Switch ====
==== The Gain Switch ====
A MOSFET switch the effective collector resistor in the first stage of the summing circuit between about 3 kΩ due to R<sub>e</sub> alone and the parallel path of 165 Ω. NXP's BF1108R has been selected for prototyping. Its typical <math>V_{GS}</math> for current pinch-off is -3 V (max: -4 V). Putting its source on the supply rail and switching the gate between 5 V (on) and 0 V (off). A bypass capacitor (not shown in diagram) near the gate lead is important to prevent spurious switching.
A MOSFET switches the effective collector resistance in the first stage of the summing circuit between about 3.3 kΩ due to R<sub>e</sub> alone and about 80 Ω for the parallel path. NXP's BF1108R has been selected for prototyping. Its typical <math>V_{GS}</math> for current pinch-off is -3 V (max: -4 V). Putting its source on the supply rail and switching the gate between 5 V (on) and 0 V (off). A bypass capacitor (not shown in diagram) near the gate lead is important to prevent spurious switching.
==== Final Performance Parameters ====
==== Final Performance Parameters ====