Return-Path: X-Spam-DCC: paranoid 1233; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: * X-Spam-Status: No, score=1.6 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, HTML_MESSAGE,HTML_TINY_FONT,RATWARE_GECKO_BUILD autolearn=no version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id u1MKLRTG006611 for ; Mon, 22 Feb 2016 21:21:27 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1aXwtm-0006Yq-0L for rs_out_1@blacksheep.org; Mon, 22 Feb 2016 20:16:02 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1aXwtk-0006Yh-UA for rsgb_lf_group@blacksheep.org; Mon, 22 Feb 2016 20:16:00 +0000 Received: from mailfe07.swip.net ([212.247.154.193] helo=swip.net) by relay1.thorcom.net with esmtp (Exim 4.86) (envelope-from ) id 1aXwsq-0007v3-5j for rsgb_lf_group@blacksheep.org; Mon, 22 Feb 2016 20:15:59 +0000 X-T2-Spam-Status: No, hits=-1.8 required=5.0 tests=BAYES_00, HTML_FONT_LOW_CONTRAST,HTML_MESSAGE Received: from [81.224.101.198] (account cxu-dcw-tyr@tele2.se HELO [192.168.1.6]) by mailfe07.swip.net (CommuniGate Pro SMTP 5.4.4) with ESMTPSA id 650978383 for rsgb_lf_group@blacksheep.org; Mon, 22 Feb 2016 21:14:49 +0100 To: rsgb_lf_group@blacksheep.org References: <7E7DFBB4D102A04DB5ADC88D66628A4A444D7A4A@ICTS-S-MBX1.luna.kuleuven.be> <7E7DFBB4D102A04DB5ADC88D66628A4A444D7A6C@ICTS-S-MBX1.luna.kuleuven.be> From: Johan Bodin Message-ID: <56CB6C3A.5080506@tele2.se> Date: Mon, 22 Feb 2016 21:14:50 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: X-HELO-Warning: Remote host 212.247.154.193 (mailfe07.swip.net) used invalid HELO/EHLO swip.net - verification failed X-Scan-Signature: 1a0ff5bc59f36a18b14a5c1a91beb3f9 Subject: Re: LF: RE: [rsgb_lf_group] Single Stage Class-B Content-Type: multipart/alternative; boundary="------------060701050407070104060603" X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Scanned-By: MIMEDefang 2.56 on 10.1.3.10 Status: O X-Status: X-Keywords: X-UID: 6946 This is a multi-part message in MIME format. --------------060701050407070104060603 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Another advantage of the push-pull amplifier is that the output signal is symmetrical (assuming the drive is too). A perfectly symmetrical waveform contains no even harmonics whatsoever, regardless of other distorsion, so the first harmonic to really worry about is 3f which is much further away and easier to filter out than 2f when compared to the wanted f. Johan SM6LKM Den 2016-02-22 kl. 20:13, skrev Andy Talbot: > That is the task of the resonant tank circuit, to maintain the RF > current flow throughout the device during the off period. > > During the off period, the drain volts have to fly up to 2.Vdd to keep > it operating linearly, and the resonant network has to ensure that > happens. > > The concept is quite standard, used for most bipolar and FET output > stages at low power (watts, tens of watts) at VHF and UHF. Although > I've noticed that modern FET amplifier modules do run at a higher > standing current and lower efficiency than bipolar ones. All the old > valved SSB transmitters of a bygone era use that topology > > I may need another long walk to ponder in more depth ... > > Andy G4JNt > > On 22 February 2016 at 18:53, Rik Strobbe > wrote: > > A single stage class B amplifies the signal over 180 degrees (ie. > half the sine). > > As long as the amplifier is not saturated the amplitude at the > output is almost linear proportional to the input amplitude, but > the signal is distorted due to the fact that half of the sine is > missing. > > In a class B push-pull each FET (or bipolar transistor, tube) will > amplify the "opposite" 180 degrees of the input signal and these > will combine at the output , so apart from the cross-over > distortion the output signal in pretty undistorted. > > 73, Rik ON7YD - OR7T > > ------------------------------------------------------------------------ > *Van:* rsgb_lf_group@yahoogroups.co.uk > > [rsgb_lf_group@yahoogroups.co.uk > ] > *Verzonden:* maandag 22 februari 2016 19:39 > *Aan:* rsgb_lf_group@yahoogroups.co.uk > > *CC:* rsgb_lf_group@blacksheep.org > > *Onderwerp:* Re: [rsgb_lf_group] Single Stage Class-B > > There's nothing inherently "more linear" about push pull over a > single stage, given you run the same device at the same power per > stage (ie half the PP level) > > 'jnt > > > On 22 February 2016 at 18:34, Rik Strobbe > rik.strobbe@fys.kuleuven.be > [rsgb_lf_group] > wrote: > > Hello Andy, > > the advantage of a push-pull class B amplifier is that it it > pretty linear at higher power levels. > > 73, Rik ON7YD - OR7T > > ------------------------------------------------------------------------ > *Van:* rsgb_lf_group@yahoogroups.co.uk > > [rsgb_lf_group@yahoogroups.co.uk > ] > *Verzonden:* maandag 22 februari 2016 18:31 > *Aan:* rsgb_lf_group@blacksheep.org > ; > rsgb_lf_group@yahoogroups.co.uk > > *Onderwerp:* [rsgb_lf_group] Single Stage Class-B > > Whilst out walking and pondering, as one does.... > > There are hundreds of designs out there for linear power > amps using FETS. They all use a similar design, push-pull > with centre tapped ferrite cored transformers at input and > output, often with resistive feedback - and all broadband. The > design is so standard it's become tedious ... and as I > don't do tedious, it made me think: > > Back in days of yore when those big bottles ruled the roost , > apart from a few designs for UHF, they were all single ended. > > So, why not a single ended MOSFET amp (for single band > operation)? We're used to seeing single device for class-E, > where the tank circuit does much of the waveform cleaning, and > reduces the low pass filter requirements. So what's wrong with > a tank-based design for class-B? > > A single ended amp can even be made ferrite free (although a > final stage DC feed choke would no doubt benefit from it). > Apart from a few very low power designs, I don't recall seeing > any designs for single band ferrite free linear amps using > power MOSFETS. > Only major downsides I visualise is that load resistance at > the device is 4 times lower for the same Vdd and Pout , and > device dissipation is doubled > > Has no one ever bothered, because broadband transformer > push-pull is so straightforward? > Has a trick been missed? > > Andy G4JNT > > > > __._,_.___ > ------------------------------------------------------------------------ > Posted by: Andy Talbot > > ------------------------------------------------------------------------ > Reply via web post > > • Reply to sender > > • Reply to group > > • Start a new topic > > • Messages in this topic > > (3) > > Visit Your Group > > > > Yahoo! Groups > > > • Privacy > • > Unsubscribe > > • Terms of Use > > > . > > __,_._,___ > > --------------060701050407070104060603 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit Another advantage of the push-pull amplifier is that the output signal is symmetrical (assuming the drive is too). A perfectly symmetrical waveform contains no even harmonics whatsoever, regardless of other distorsion, so the first harmonic to really worry about is 3f which is much further away and easier to filter out than 2f when compared to the wanted f.

Johan SM6LKM

Den 2016-02-22 kl. 20:13, skrev Andy Talbot:
That is the task of the resonant tank circuit, to maintain the RF current flow throughout the device during the off period. 

During the off period, the drain volts have to fly up to 2.Vdd to keep it operating linearly, and the resonant network has to ensure that happens.

The concept is quite standard, used for most bipolar and FET output stages at low power (watts, tens of watts)  at VHF and UHF.   Although I've noticed that modern FET amplifier modules do run at a higher standing current and lower efficiency than bipolar ones.   All the old valved SSB transmitters of a bygone era use that topology

I may need another long walk to ponder in more depth ...

Andy  G4JNt

On 22 February 2016 at 18:53, Rik Strobbe <rik.strobbe@fys.kuleuven.be> wrote:

A single stage class B amplifies the signal over 180 degrees (ie. half the sine).

As long as the amplifier is not saturated the amplitude at the output is almost linear proportional to the input amplitude, but the signal is distorted due to the fact that half of the sine is missing.

In a class B push-pull each FET (or bipolar transistor, tube) will amplify the "opposite" 180 degrees of the input signal and these will combine at the output , so apart from the cross-over distortion the output signal in pretty undistorted.

 

73, Rik  ON7YD - OR7T

 

Van: rsgb_lf_group@yahoogroups.co.uk [rsgb_lf_group@yahoogroups.co.uk]
Verzonden: maandag 22 februari 2016 19:39
Aan: rsgb_lf_group@yahoogroups.co.uk
CC: rsgb_lf_group@blacksheep.org
Onderwerp: Re: [rsgb_lf_group] Single Stage Class-B

 
There's nothing inherently "more linear" about push pull over a single stage, given you run the same device at the same power per stage (ie half the PP level)    

'jnt


On 22 February 2016 at 18:34, Rik Strobbe rik.strobbe@fys.kuleuven.be [rsgb_lf_group] <rsgb_lf_group@yahoogroups.co.uk> wrote:
 

Hello Andy,

 

the advantage of a push-pull class B amplifier is that it it pretty linear at higher power levels.

 

73, Rik  ON7YD - OR7T

 

Van: rsgb_lf_group@yahoogroups.co.uk [rsgb_lf_group@yahoogroups.co.uk]
Verzonden: maandag 22 februari 2016 18:31
Aan: rsgb_lf_group@blacksheep.org; rsgb_lf_group@yahoogroups.co.uk
Onderwerp: [rsgb_lf_group] Single Stage Class-B

 
Whilst out walking and pondering, as one does....

There are hundreds of designs out there for  linear power amps using FETS.  They all use a similar design, push-pull with centre tapped ferrite cored transformers at input and output, often with resistive feedback - and all broadband.   The design is so standard it's become tedious ... and as I don't do tedious, it made me think:

Back in days of yore when those big bottles ruled the roost ,  apart from a few designs for UHF, they were all single ended.

So, why not a single ended MOSFET amp (for single band operation)?   We're used to seeing single device  for class-E, where the tank circuit does much of the waveform cleaning, and reduces the low pass filter requirements.    So what's wrong with a tank-based  design for class-B?

A single ended amp can even be made ferrite free (although a final stage DC feed choke would no doubt benefit from it).   Apart from a few very low power designs, I don't recall seeing any designs for single band ferrite free linear amps using power MOSFETS. 
Only major downsides I visualise is that load resistance at the device is 4 times lower for the same Vdd and Pout , and device dissipation is doubled

Has no one ever bothered, because broadband transformer push-pull is so straightforward?
Has a trick been missed?  

Andy  G4JNT



__._,_.___
Posted by: Andy Talbot <andy.g4jnt@gmail.com>
Reply via web post • Reply to sender • Reply to group • Start a new topic • Messages in this topic (3)

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