Designing a JFET-JFET Cascode Amplifier: Tips and Resources

  • Thread starter Keep_i_real
  • Start date
  • Tags
    Amplifier
In summary, Mark is looking to build a FET-FET cascode preamplifier and has shared his current setup, which includes two JFETs (2N3819) and resistors and capacitors. He has tried to derive equations for the JFETs in order to determine the values for the resistors and capacitors, but has been unsuccessful. He is looking for help and recommendations for resources on how to properly bias JFETs. The key factor in biasing JFETs is ensuring that the gate is at a lower potential than the source, and this can be calculated using a quadratic equation. The two necessary parameters for biasing calculations are the pinch-off voltage (Vp) and the
  • #1
Keep_i_real
10
0
Hi. I'm not actually doing an electronics course (Maths & Physics), but I have just finished building a 140W BJT guitar power amplifier and cabinet. I'm looking to build a FET-FET cascode preamplifier now, but am not too familiar with JFETs - So far, I've got:

V+
|
Resistor
|
JFET2 (2N3819)
|
Resistor
|
JFET1 (2N3819)
|
Resistor & capacitor (parallel)
|
Ground

with the input on the gate of JFET1, output from the source of JFET2, and the base of JFET 2 tied to ground.

I've tried to derrive equations for the JFETs, in order to work out the values for the resistors and capacitors, but with no success - can anyone here help me, or point me to any good books/websites?

Cheers,
Mark
 
Last edited:
Engineering news on Phys.org
  • #2
When biasing Jfets, Gate has to be at a lower potential than the source. That's when drain to source current stars flowing. Drain to source current depends on gate voltage, and can be calculated using a quadratic equation.

When doing biasing calculations on jfets, two parameters are needed, the pinchoff voltage Vp, and the saturation current Idd. You can obtain these from the datasheet, or measure them easily.

I googled jfet biasing and there is a plenty of tutorials.

http://www.qrp.pops.net/fetbias.asp

Hope that helps.
 
  • #3
Cheers!
 

1. What is a JFET-JFET cascode amplifier?

A JFET-JFET cascode amplifier is a type of electronic circuit that uses two JFET (junction field-effect transistor) devices connected in a specific configuration to amplify an input signal. The cascode configuration allows for a higher gain and a wider bandwidth compared to a single JFET amplifier.

2. How does a JFET-JFET cascode amplifier work?

In a JFET-JFET cascode amplifier, the first JFET serves as a high input impedance voltage amplifier, while the second JFET acts as a low output impedance current amplifier. This configuration allows for a higher gain and a wider bandwidth, making it suitable for use in high-frequency applications.

3. What are the advantages of using a JFET-JFET cascode amplifier?

Some advantages of using a JFET-JFET cascode amplifier include a higher gain, wider bandwidth, and improved linearity compared to a single JFET amplifier. It also has a low output impedance, making it suitable for driving reactive loads.

4. What are some common applications of JFET-JFET cascode amplifiers?

JFET-JFET cascode amplifiers are commonly used in high-frequency applications such as radio frequency (RF) amplifiers, mixers, and oscillators. They are also used in audio amplifiers and instrumentation amplifiers.

5. Are there any disadvantages of using a JFET-JFET cascode amplifier?

One potential disadvantage of JFET-JFET cascode amplifiers is their relatively high cost compared to other amplifier configurations. Additionally, they require precise matching of the two JFET devices, which can be challenging to achieve in some cases.

Similar threads

Replies
17
Views
10K
  • Electrical Engineering
Replies
4
Views
2K
  • Electrical Engineering
Replies
2
Views
7K
  • Electrical Engineering
Replies
9
Views
10K
  • Electrical Engineering
Replies
5
Views
6K
Back
Top