Ode to Lateral MOSFETs - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 29th September 2007, 05:47 PM   #1
Banned
 
Join Date: Apr 2005
Location: Stockholm
Default Ode to Lateral MOSFETs

Is there anybody interested in this kind of contribution to the constant ongoing discussion, verticals vs laterals?

Once upon a time, maybe Anno Domini 1977, Hitachi announced its S series stating the lateral structure was used in order to achieve enhanced high frequency and gain performance and low gate-drain capacitance.
The predominant vertical MOSFET topology has due to huge industrial demand been subject of massive continuous research and development. However, the lateral topology encompasses features which can not be replicated by any means.
Linear transfer means, most importantly, low intermodulation distortion . High bandwidth, in subjective terms, signifies a soft, musical and less distorted sound, characterizing a large spectrum of the audible frequency range.

Parameters of MOSFETs regarding transfer and high frequency performance:
Idss = saturated drain (cut-off) current. High Idss values have the penalty of increased Crss and Ciss.
Rdson = static drain-source on resistance. Low Rdson brings about high Coss. Rdson increases with increasing temperature.
W = channel width.
L = channel length. A crucial structural difference. L is very short and more precisely defined for laterals offering several advantages like low Crss.
In the case of verticals, the lack of close control over the device characteristics in the vertical dimension results in longer channel lengths, increased leakage current, and increased parasitic capacitances. A large W/L ratio is necessary to achieve high Idss and low Rdson values being important for switching but that is not possible without increasing certain capacitances.
VGSth = the minimum gate bias voltage which enables the formation of the channel between drain and source.
Gm = forward transconductance. The ratio of a change in AC output current to a change in AC input voltage at other parameters fixed. Gm is proportional to W/L. Gm decreases with increasing temperature.
ft = maximum frequency of operation. ft is directly proportional to Gm and inversely proportional to Ciss and to L.
Capacitances supplied by manufactures in data sheets:
Ciss = input capacitance, the sum of Cgs and Cgd. Cgd is small compared to Cds.
Coss = output capacitance, the sum of Cgd and Cds. It is mainly a junction capacitance having its highest value at Vgs = 0, decreasing with increasing Vds, its minimum value specified at a given Vds. Coss is directly proportional to W/L.
Crss = reverse transfer or feedback Miller capacitance, same as Cdg, suffers from voltage gain multiplication. Despite being the lowest value compared to Ciss and Coss, it has the most devastating effect on high frequency performance, thus on the sound. Low Crss values reduce Idss.
For good high frequency performance a low ratio of Crss/Coss and even more importantly a high ratio of Gm/Crss is essential.
High Gm is required also for high power gain and linearity, obtained at low gate voltages and having flat characteristics over a wide range of gate voltage.
In conclusion: large power handling capability has an inevitable price. Because of its construction vertical MOSFETs can not challenge the linear transfer characteristics and high frequency performance of laterals.
  Reply With Quote
Old 29th September 2007, 06:04 PM   #2
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Read the Bob Cordell MOSFET thread.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 29th September 2007, 06:07 PM   #3
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
I think that what you wrote classicists would more correctly describe as a "paean" rather than an "ode".
  Reply With Quote
Old 29th September 2007, 08:53 PM   #4
hihopes is offline hihopes  South Africa
diyAudio Member
 
Join Date: Sep 2004
Location: Cape Town
Very informative Lumba. I now feel much happier about my laterals.
  Reply With Quote
Old 2nd October 2007, 03:26 PM   #5
Banned
 
Join Date: Apr 2005
Location: Stockholm
jackinnj ,
right, you are thoroughly conversant with Greek mythology...
  Reply With Quote
Old 2nd October 2007, 03:34 PM   #6
diyAudio Member
 
Workhorse's Avatar
 
Join Date: Dec 2004
Default Re: Ode to Lateral MOSFETs

Quote:
Originally posted by Lumba Ogir
In conclusion: large power handling capability has an inevitable price. Because of its construction vertical MOSFETs can not challenge the linear transfer characteristics and high frequency performance of laterals.
Think once more while talking about the challenge for Verticals
  Reply With Quote
Old 2nd October 2007, 03:45 PM   #7
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
Originally posted by Lumba Ogir
jackinnj ,
right, you are thoroughly conversant with Greek mythology...
8 years of Jesuits.

It is going to be really interesting to hear Mark Brasfield's presentation at the AES conference next Monday. Mark wrote the application note on the LM4702 -- which Troy Huebner updated to use lateral MOSFETs.
  Reply With Quote
Old 2nd October 2007, 09:24 PM   #8
mlloyd1 is offline mlloyd1  United States
diyAudio Member
 
mlloyd1's Avatar
 
Join Date: Feb 2001
Location: illinois
yeah, wish i was going.
i hope National puts together one of their road shows after the conference. would be interesting ...

mlloyd1

Quote:
Originally posted by jackinnj
... It is going to be really interesting to hear Mark Brasfield's presentation at the AES conference next Monday ...
  Reply With Quote
Old 11th June 2008, 08:31 AM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Is anyone going to tell us how to take the apparent disadvantages of Verticals and use them to the benefit of us Audioistas?

Some have done it and done it very well, but what technically needs doing to achieve the desired end.
We can copy a successful design, but let's help us go further.
__________________
regards Andrew T.
  Reply With Quote
Old 11th June 2008, 10:26 AM   #10
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
I like lateral mosfets but this is mostly because I have only used those in my designs. On thing is good: The gm is rather constant = low distortion
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
New Lateral MOSFETs Just Released! The Saint Aussie Amplifiers 41 14th November 2009 09:52 PM
Lateral Mosfets for sale Fanuc Swap Meet 20 28th March 2009 10:17 AM
Substitute Lateral Mosfets joensd Parts 33 21st December 2008 01:57 PM
Lateral mosfets - why ? Stormo Solid State 5 2nd July 2003 07:14 AM


New To Site? Need Help?

All times are GMT. The time now is 04:49 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2