These are circuits of high impedance low capacitance buffer and high impedance low capacitance amplifier. First figure is a high impedance low capacitance buffer circuit, it uses the 2N446 JFET that features low input capacitance. The feedback buffer a wide-band unity gain amplifier is made from this 2N446 JFET. Here is the circuit :
The second figure is high impedance low capacitance amplifier. This circuit provides high input impedance and stable. This circuit has wide-band gain that is used for general purpose video amplifier applications. The gain of the amplifier is equal to R2/R1. [Source: National Semiconductor Application Note]
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