A current mirror variation on the Baxandall Class-D oscillator for producing a reasonable clean sine wave....

[Bill Sloman]

I\'ve up-dated my website to add a circuit diagram, some comment on it, and the text from the corresponding LTSpice .asc file.

http://sophia-electronica.com/BillsBaxandall.html

The circuit produces a balanced pair of 1V rms 17kHz sine waves. The LTSpice simulation suggests the third harmonic content is about 60db below the fundamental, and the fifth harmonic is even smaller.

It\'s not a particularly simple circuit, and would take quite a bit of fiddling to get it to work at a significantly different frequency - all of it fairly obvious.

It exploits an asymmetrical current mirror to provide the gain that sustains the oscillation, and tweaks the - linear - gain in the mirror to stabilise the output swing.

--
Bill Sloman, Sydney

 

[Tony Stewart]

On Wed. 12 Aug.-20 4:46 a.m., Bill Sloman wrote:

I\'ve up-dated my website to add a circuit diagram, some comment on it, and the text from the corresponding LTSpice .asc file.

http://sophia-electronica.com/BillsBaxandall.html

The circuit produces a balanced pair of 1V rms 17kHz sine waves. The LTSpice simulation suggests the third harmonic content is about 60db below the fundamental, and the fifth harmonic is even smaller.

It\'s not a particularly simple circuit, and would take quite a bit of fiddling to get it to work at a significantly different frequency - all of it fairly obvious.

It exploits an asymmetrical current mirror to provide the gain that sustains the oscillation, and tweaks the - linear - gain in the mirror to stabilise the output swing.

Do happen to recall the specs for THD, startup time?

 

[Tony Stewart]

On Wed. 12 Aug.-20 4:46 a.m., Bill Sloman wrote:

I\'ve up-dated my website to add a circuit diagram, some comment on it, and the text from the corresponding LTSpice .asc file.

http://sophia-electronica.com/BillsBaxandall.html

The circuit produces a balanced pair of 1V rms 17kHz sine waves. The LTSpice simulation suggests the third harmonic content is about 60db below the fundamental, and the fifth harmonic is even smaller.

It\'s not a particularly simple circuit, and would take quite a bit of fiddling to get it to work at a significantly different frequency - all of it fairly obvious.

It exploits an asymmetrical current mirror to provide the gain that sustains the oscillation, and tweaks the - linear - gain in the mirror to stabilise the output swing.

Never mind my last question.

So I made a quick and dirty NPN Wein OSC 12.00Vpp 77kHz , instant
startup and stabilizes in a few cycles with soft limiting using a diode +RC.

http://tinyurl.com/y2d8usla

 

[Bill Sloman]

On Friday, August 14, 2020 at 3:59:30 PM UTC+10, Anthony Stewart wrote:

On Wed. 12 Aug.-20 4:46 a.m., Bill Sloman wrote:
I\'ve up-dated my website to add a circuit diagram, some comment on it, and the text from the corresponding LTSpice .asc file.

http://sophia-electronica.com/BillsBaxandall.html

The circuit produces a balanced pair of 1V rms 17kHz sine waves. The LTSpice simulation suggests the third harmonic content is about 60db below the fundamental, and the fifth harmonic is even smaller.

It\'s not a particularly simple circuit, and would take quite a bit of fiddling to get it to work at a significantly different frequency - all of it fairly obvious.

It exploits an asymmetrical current mirror to provide the gain that sustains the oscillation, and tweaks the - linear - gain in the mirror to stabilise the output swing.

Never mind my last question.

So I made a quick and dirty NPN Wein OSC 12.00Vpp 77kHz , instant
startup and stabilizes in a few cycles with soft limiting using a diode +RC.

http://tinyurl.com/y2d8usla

It\'s not a Wien bridge, but a phase shift oscillator. There\'s no obvious amplitude control, so it presumably relies on clipping against the rails, which introduces is own distortion.

https://en.wikipedia.org/wiki/Phase-shift_oscillator

Wien bridges all need some kind of gain control element, and if you want clean sine wave with well-controlled amplitude (which I did when I invented the circuit) the options are limited.

--
Bill Sloman, Sydney

 

[server]

On Fri, 14 Aug 2020 01:59:23 -0400, Tony Stewart
<tony.sunnysky@gmail.com> wrote:

On Wed. 12 Aug.-20 4:46 a.m., Bill Sloman wrote:
I\'ve up-dated my website to add a circuit diagram, some comment on it, and the text from the corresponding LTSpice .asc file.

http://sophia-electronica.com/BillsBaxandall.html

The circuit produces a balanced pair of 1V rms 17kHz sine waves. The LTSpice simulation suggests the third harmonic content is about 60db below the fundamental, and the fifth harmonic is even smaller.

It\'s not a particularly simple circuit, and would take quite a bit of fiddling to get it to work at a significantly different frequency - all of it fairly obvious.

It exploits an asymmetrical current mirror to provide the gain that sustains the oscillation, and tweaks the - linear - gain in the mirror to stabilise the output swing.



Never mind my last question.

So I made a quick and dirty NPN Wein OSC 12.00Vpp 77kHz , instant
startup and stabilizes in a few cycles with soft limiting using a diode +RC.

http://tinyurl.com/y2d8usla

That\'s actually a phase-shift oscillator. They typically have a lot of
distortion. They can be fiddled to have marginal loop gain, to
minimize distortion at the cost of reliability. They are hard to tune!

I might Spice my weird resonant phase-shift oscillator idea this
weekend.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Kevin Aylward]

\"Tony Stewart\" wrote in message news:rh583k$1pt3$1@gioia.aioe.org...

On Wed. 12 Aug.-20 4:46 a.m., Bill Sloman wrote:

I\'ve up-dated my website to add a circuit diagram, some comment on it, and
the text from the corresponding LTSpice .asc file.

http://sophia-electronica.com/BillsBaxandall.html

The circuit produces a balanced pair of 1V rms 17kHz sine waves. The
LTSpice simulation suggests the third harmonic content is about 60db below
the fundamental, and the fifth harmonic is even smaller.

It\'s not a particularly simple circuit, and would take quite a bit of
fiddling to get it to work at a significantly different frequency - all of
it fairly obvious.

Yeah...Its way complicated. Like 6 inductors!!!

What actual design problem is the circuit trying to solve that this
topology is alleged to be superior to than the others?. Accuracy?
Distortion? Supply current? Supply rejection? Start-up time? Phase noise?

At this frequency, they are way simpler and cheaper methods to get a low
distortion sine wave.

-- Kevin Aylward
http://www.anasoft.co.uk - SuperSpice
http://www.kevinaylward.co.uk/ee/index.html

 

[whit3rd]

On Saturday, August 15, 2020 at 8:27:15 AM UTC-7, Kevin Aylward wrote:

\"Tony Stewart\" wrote in message news:rh583k$1pt3$1@gioia.aioe.org...

On Wed. 12 Aug.-20 4:46 a.m., Bill Sloman wrote:
I\'ve up-dated my website to add a circuit diagram, some comment on it, and ...

It\'s not a particularly simple circuit, and would take quite a bit of
fiddling to get it to work at a significantly different frequency - all of
it fairly obvious.

Yeah...Its way complicated. Like 6 inductors!!!

What actual design problem is the circuit trying to solve that this
topology is alleged to be superior to than the others?. Accuracy?
Distortion? Supply current? Supply rejection? Start-up time? Phase noise?

My read on the inductors, is... they\'re windings on a single core. One inductor.
Startup time is better than a (for instance) noise-dependent crystal oscillator,
and phase noise will beat an RC (like Wein bridge) design.

Don\'t know why anyone sees a phase-shift oscillator here, it\'s just using some power-supply
regulation of currents, to keep the transistors all out of saturation.

 

[Bill Sloman]

On Sunday, August 16, 2020 at 1:27:15 AM UTC+10, Kevin Aylward wrote:

\"Tony Stewart\" wrote in message news:rh583k$1pt3$1...@gioia.aioe.org...
On Wed. 12 Aug.-20 4:46 a.m., Bill Sloman wrote:
I\'ve up-dated my website to add a circuit diagram, some comment on it, and
the text from the corresponding LTSpice .asc file.

http://sophia-electronica.com/BillsBaxandall.html

The circuit produces a balanced pair of 1V rms 17kHz sine waves. The
LTSpice simulation suggests the third harmonic content is about 60db below
the fundamental, and the fifth harmonic is even smaller.

It\'s not a particularly simple circuit, and would take quite a bit of
fiddling to get it to work at a significantly different frequency - all of
it fairly obvious.

Yeah...Its way complicated. Like 6 inductors!!!

Don\'t be silly. That\'s six windings in one transformer

You should know enough about Spice to be able to decode \"K1 L1 L2 L3 L4 L5 L6 0.99 \"

What actual design problem is the circuit trying to solve that this
topology is alleged to be superior to than the others?. Accuracy?
Distortion? Supply current? Supply rejection? Start-up time? Phase noise?

From my web-site

http://sophia-elektronica.com/Baxandall_parallel-resonant_Class-D_oscillator1.htm

\"This circuit was originally developed as a retrofit to excite a linear variable differential transformer used to measure the progressively increasing mass of a single crystal of gallium arsenide (GaAs) being grown in the Metals Research GaAs Liquid-Encapsulated Czochralski (LEC) crystal puller.\"

I needed a very stable amplitude for the sine wave excitation - and the LVDT happened to have a spare winding (originally intended to drive a demodulator) which I demodulated (with a copy of the signal demodulator circuit) to monitor the excitation voltage I was feeding into the LVDT. I wanted a fairly clean sine wave - the switching demodulator was sensitive to odd harmonic content - and I had to get the whole circuit onto a rather small printed circuit board which sat in a rather confined space above the crystal puller that happened to rotate with the crystal. All the signals went in and out through silver brushes - not my choice. The whole thing was designed as retrofit. The operators liked it a whole lot better than the original circuit, but mainly because I\'d taken out the original uA741 on the output - which suffered from pop-corn noise - and replaced it with a next generation part - possibly the OP07 - which actually had a low frequency input noise specification. The effect was that the radio-frequency heating of the GaAs crucible stayed constant at about 40% of full scale, when before it had used to pulse-width modulate with a roughly 90 second period. I liked to claim that this improved the quality of the GaAs single crystals we pulled, but there\'s absolutely no evidence that this was true. My next project used Gigabit Logic\'s GaAs parts, so I would claim - purely for comic effect - that I\'d taken on the project to get myself better GaAs parts. The reality was that the guy who had done the electronic design for the original version of the crystal puller - some ten years earlier - was great at putting together stuff that worked - and kept on working - but rather slap-dash, and I spent a year getting rid of his more desperate improvisations.

The 741 I got rid off had been driving a long cable - long enough to persuade it to oscillate - and my predecessor had \"cured\" the oscillation by loading the output with 100nF to ground (making the amplitude too low to be visible). I put in the usual fix for a capacitative load when I reworked the circuit.

At this frequency, there are way simpler and cheaper methods to get a low
distortion sine wave.

Name one. A Wien Bridge wouldn\'t have been any simpler, and would have used more power to do the job.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Sunday, August 16, 2020 at 10:36:21 AM UTC+10, whit3rd wrote:

On Saturday, August 15, 2020 at 8:27:15 AM UTC-7, Kevin Aylward wrote:
\"Tony Stewart\" wrote in message news:rh583k$1pt3$1...@gioia.aioe.org...

On Wed. 12 Aug.-20 4:46 a.m., Bill Sloman wrote:
I\'ve up-dated my website to add a circuit diagram, some comment on it, and ...
It\'s not a particularly simple circuit, and would take quite a bit of
fiddling to get it to work at a significantly different frequency - all of
it fairly obvious.

Yeah...Its way complicated. Like 6 inductors!!!

What actual design problem is the circuit trying to solve that this
topology is alleged to be superior to than the others?. Accuracy?
Distortion? Supply current? Supply rejection? Start-up time? Phase noise?
My read on the inductors, is... they\'re windings on a single core. One inductor.
Startup time is better than a (for instance) noise-dependent crystal oscillator,
and phase noise will beat an RC (like Wein bridge) design.

Don\'t know why anyone sees a phase-shift oscillator here, it\'s just using some power-supply
regulation of currents, to keep the transistors all out of saturation.

The phase-shift oscillator was Anthony Stewart\'s proposed alternative - and he called it a Wien Bridge. Actually a Wein Bridge, for added extra comic effect.

The regulation does keep the transistors out of saturation, but in the original circuit the aim was to get a very well-defined - and stable output amplitude.

Monitoring the voltage at the centre-tap isn\'t a particularly good way of doing this, but it does keep the proof-of-principle circuit relatively simple.

--
Bill Sloman, Sydney