Breaking News
Comments
Newest First | Oldest First | Threaded View
kendallcp
User Rank
Rookie
re: Discrete audio amplifier basics - Part 2: JFETs, MOSFETs and other circuit configurations
kendallcp   7/20/2010 12:34:31 PM
NO RATINGS
It's lovely to see such extended treatment of JFET amplifiers. How many other people out there get the same rather wistful feeling that I do, though? The big semiconductor manufacturers have culled their JFET ranges to extinction, leaving the market mostly to specialist vendors such as Linear Systems. Depletion-mode FETs have the wonderful characteristic of being conducting when no gate potential is applied; this behaviour is really hard to replicate otherhow. There are a few depletion MOS devices out there; single-source and in quite large packages. I feel rather sad that the JFET is slowly fading from our design consciousness. What do you think?

WKetel
User Rank
Rookie
re: Discrete audio amplifier basics - Part 2: JFETs, MOSFETs and other circuit configurations
WKetel   4/1/2010 12:18:46 AM
NO RATINGS
This explanation of the symbols is useful. Now I need to convince others that it has value.

bcarso
User Rank
Rookie
re: Discrete audio amplifier basics - Part 2: JFETs, MOSFETs and other circuit configurations
bcarso   3/28/2010 8:09:16 PM
NO RATINGS
You need to establish a base bias suffficent to operate the lower device in/near the pinchoff region, i.e., where its output impedance is reasonably high. You do not want the base voltage to (partially) track with the circuit output voltage---this tends to defeat the purpose of the cascade, which is to minimize the voltage swing on the drain of the input device, thus reducing drain-gate capacitance multiplication ("Miller effect"). In some cases it is advantageous to derive the base voltage from a sample of the actual circuit input voltage, reducing the effective FET input capacitance further---however, this will result in negative input impedance at high frequencies and potential instabilities.

wreeve
User Rank
Rookie
re: Discrete audio amplifier basics - Part 2: JFETs, MOSFETs and other circuit configurations
wreeve   3/28/2010 4:39:18 AM
NO RATINGS
I would like to explore the cascode configuration of fig. 9.15 but with Q2 replaced with a BJT. My question concerns biasing of Q2 when it is a BJT in a common base configuration. Does it matter if the base biasing resistor is connected directly to Vcc or the bottom of R2 where the Output is tapped? How do both arrangements affect the overall cascode circuit gain?



Flash Poll
EE Life
Frankenstein's Fix, Teardowns, Sideshows, Design Contests, Reader Content & More
Rishabh N. Mahajani, High School Senior and Future Engineer

Future Engineers: Don’t 'Trip Up' on Your College Road Trip
Rishabh N. Mahajani, High School Senior and Future Engineer
2 comments
A future engineer shares his impressions of a recent tour of top schools and offers advice on making the most of the time-honored tradition of the college road trip.

Max Maxfield

Juggling a Cornucopia of Projects
Max Maxfield
7 comments
I feel like I'm juggling a lot of hobby projects at the moment. The problem is that I can't juggle. Actually, that's not strictly true -- I can juggle ten fine china dinner plates, but ...

Larry Desjardin

Engineers Should Study Finance: 5 Reasons Why
Larry Desjardin
37 comments
I'm a big proponent of engineers learning financial basics. Why? Because engineers are making decisions all the time, in multiple ways. Having a good financial understanding guides these ...

Karen Field

July Cartoon Caption Contest: Let's Talk Some Trash
Karen Field
139 comments
Steve Jobs allegedly got his start by dumpster diving with the Computer Club at Homestead High in the early 1970s.

Top Comments of the Week
Like Us on Facebook
EE Times on Twitter
EE Times Twitter Feed

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)