high input impedance voltage follower

high input impedance voltage follower hones, as an It is common knowledge that Field Effect Tran- well sistors (F ETs) feature a very high impedance — we within the Giga-ohm range, in fact. As showinc he on- circuit diagram, one F ET is quite enough to struct a buffer amplifier with an input impedance of 1 GSZ. The circuit is simply an impedance converter (source follower) with a gain of 1 and can be used for a variety of applications, such as a buffer for edance (capacitor) microp high imp oscilloscope probe etc. One way to obtain the required input impedance is to connect a 1 GO. resistor between the gate of the 4 th o a 4. 14. 6 4i i BF256 A C3 tor C2 as a form of "bootstrap". Theoretically, the 12...30v 0q,2 mA FET and ground. Unfortunately, such high value resistors are not only difficult to obtain, but they are also rather expensive and so a cheaper alter- naR2tive will have to be found. This particular circuit gets around the problem nicely by utilising capaci- h input ...