Need Help design Jfet front end Amp

[bobcat1]

Need Help design Jfet front end Amp

input impdance 80 Ohm

gain 5 - 10

oprating voltage 5V

frequency responce : 1 - 15 Mhz

Can I do that with BF245 ?

thanks


bobi



bobi

 

[flatulent]

some problems

This transistor can have a pinchoff voltage larger than your power supply. You should choose a transistor with a pinchoff of about a third or quarter of the power supply voltage.

Here are some pointers.

1. Use a common source configruation
2. The resistor from source to ground will set the real part of the input impedance.
3. The source resistor will set the drain current to be in the neighborhood of the pinchoff voltage divided by the source resistor.

4. For the drain load you can either use a resistor between the drain and the power supply, or you can use a transformer primary with the load resistor across the secondary.

5. The gain will be near the ratio of the load to the source resistances.

6. If you want more gain, put a bypass capacitor across the source resistor.

 

[RegUser_2]

Why do U need JFET for such low impedance? The bipolar transistors got beter transconductance than the JFETS.