Re: Pease tuneable MFB band-pass filter
Figure 1 was probably drawn by an EDN person.
Bob's rough sketch is OK. I was taking the output from the wrong
place.
On 2025-05-12 08:40, Tony Casey via
groups.io wrote:
You should also note, John, that there are errors in the EDN
article.
The first picture shows the opamp in non-inverting configuration -
this is, of course positive feedback, and sure enough it will
latch to one of the rails.
Further down in the article, variations of the circuit are
re-drawn in the inverting configuration - this is the correct
version.
It is a quirk of AC analyses that sometimes an unstable
configuration appears to be stable, when in fact it isn't. Always
check in the time domain!
I presume Bob got it right. He would never have made that mistake.
I'm surprised nobody else pointed that out.
--
Regards,
Tony
On 11/05/2025 16:20, John Woodgate
via groups.io wrote:
I have uploaded the above as a .ZIP. According to
Bob Pease, the gain at the peak should be close to 34 dB,
independent of the tuned frequency. I don't get either of
those results using version 24.1.8. However, the bandwidth is
fairly constant with frequency, as predicted. I can't believe
Bob Pease reported the performance in error.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
Re: Pease tuneable MFB band-pass filter
You should also note, John, that there are errors in the EDN
article.
The first picture shows the opamp in non-inverting configuration -
this is, of course positive feedback, and sure enough it will latch
to one of the rails.
Further down in the article, variations of the circuit are re-drawn
in the inverting configuration - this is the correct version.
It is a quirk of AC analyses that sometimes an unstable
configuration appears to be stable, when in fact it isn't. Always
check in the time domain!
I presume Bob got it right. He would never have made that mistake.
I'm surprised nobody else pointed that out.
--
Regards,
Tony
On 11/05/2025 16:20, John Woodgate via
groups.io wrote:
toggle quoted message
Show quoted text
I have uploaded the above as a .ZIP. According to
Bob Pease, the gain at the peak should be close to 34 dB,
independent of the tuned frequency. I don't get either of those
results using version 24.1.8. However, the bandwidth is fairly
constant with frequency, as predicted. I can't believe Bob Pease
reported the performance in error.
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Re: Crystal oscillator oscillation startup
On Mon, May 12, 2025 at 12:33 AM, Cheng Fei Phung wrote:
Which transistors are incorrectly biased, if I may ask ?
The ones said to be in weak inversion zone so that they act as a very large resistor.? I do not know if it is a problem with biasing, or with sizes.
I did not change much the asc circuit file, I had been doing some study on the circuit operation details theory.
What changed, that makes it oscillate now?
?
Andy
?
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Re: simulating CD4007 (CD4009 ??) for linear application
On Sun, May 11, 2025 at 10:36 PM, <Eli.rosenkim@...> wrote:
I am a LTSpice novice who is looking to simulate a CD4009 chip for a linear application. Specifically, in the electronotes newsletter #111, it is hinted that these can be used to make a simple VCA. ...
Electronotes?- wow, I have not heard of them in a long time.
?
My very naive approach has been to just copy down the arrangement of NMOS and PMOS shown on the CD4009 datasheet as shown, without tweaking any parameters or selecting "pick new transistor". The circuit I am trying to simulate seems to qualitatively do what it is supposed to after some tweaking, but with the RC values and and supply voltage as shown in the original schematic, it does not achieve nearly the performance claimed. I am wondering if there is any way to select NMOS and PMOS parameters to improve my simulation's accuracy to the actual CD4009. Any help is much appreciated!
Somewhere, there might be a pair of .MODEL statements for the MOSFETs in those early CD4xxx parts.? The default NMOS and PMOS models are right for early 1970s, so the time period is about right for CD4xxx and maybe that works in your favor.? The other unknown is what are the W and L of each FET.? By default, you get W = L = 20 microns.? Fortunately the T.I. datasheet has lots of DC curves, which an enterprising student could use to compare with simulations and adjust W and L (and maybe the .MODEL parameters) to get a good fit.? Does that sound like a plan, and is the effort worth it?
?
I notice the graph from the Electronotes #111 refers to a square wave audio input signal, which maybe suggests that the circuit might not be as clean as one would want for good audio.
?
Andy
?
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Re: Crystal oscillator oscillation startup
On Mon, May 12, 2025 at 10:43 AM, Andy I wrote:
some transistors seem to be biased incorrectly as they do not behave according to your annotations
Which transistors are incorrectly biased, if I may ask ?
?
I did not change much the asc circuit file, I had been doing some study on the circuit operation details theory.
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Re: simulating CD4007 (CD4009 ??) for linear application
Oops!? I "fat-fingered" when I typed what was supposed to be "CD4009" in the Subject line.? ?I have now fixed that.
?
Sorry for messing up the messages in some of your email folders.
?
Andy
?
?
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Re: Single-phase H-bridge inverter circuit
On Sat, May 10, 2025 at 09:42 PM, <guilhermesouzam01@...> wrote:
... in our example, the power supply voltage is 5V. But what if our power supply is much higher, say around 300V? The MOSFET needs a gate-to-source voltage (Vgs) that is higher than the source (Vs) to turn on. So, if we keep using a 10V PWM signal referenced to ground, it wouldn’t work properly.
I’ve been researching this, and I came across the bootstrap driver technique. Is this commonly used in such high-voltage applications? Or is there another configuration we should use in this scenario?
What you said is correct.? There are probably a few ways to make it work.? I am not an expert on the ways to do that.
?
What you need is to apply the gate drive signal as a differential voltage between the gate and source of the pull-up FET.? For simulations (not real circuits), you can easily do that by connecting the PULSE voltage source between the gate and source pins instead of ground.? For real circuits, sometimes a miniature transformer can isolate the signal from ground, and connect it between gate and source instead.? If a transformer doesn't work, there are isolation ICs as well as opto-isolators that perform a similar function.? Also, many ICs are designed for driving MOSFETs and have internal circuits to bootstrap the signal that goes to the FET's gate pin.? I don't know if those can accommodate as much as 300 V.? But transformers can, and signal isolating ICs probably can.
?
Depending on the waveforms and a few other things, it might even work to use a capacitor to AC-couple and level-shift the voltage for the gate pin.
?
Andy
?
?
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Re: Crystal oscillator oscillation startup
On Sun, May 11, 2025 at 09:31 PM, Cheng Fei Phung wrote:
Just an FYI - it is not "attached".? It is "uploaded".? Nothing was attached to the message.
?
That is the correct way to do it.? It was just stated wrongly.
?
Andy
?
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Re: Crystal oscillator oscillation startup
Cheng Fei Phung,
?
I apologize for not replying sooner.? I was taking a look at your original oscillator circuit (with the schematic borrowed from a paper at the ieeexplore.ieee.org website).? I do not believe that schematic is workable as an oscillator, when using the transistor models and sizes that you have provided.? I think the oscillator transistor lacks sufficient gain.? Also, some transistors seem to be biased incorrectly as they do not behave according to your annotations.? I was generating curves in LTspice to illustrate.? But alas, life got in the way for me and I was delayed.
?
Have not yet seen your latest version.
?
Andy
?
?
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simulating CD4007 (CD4009 ??) for linear application
Hi! I am a LTSpice novice who is looking to simulate a CD4009 chip for a linear application. Specifically, in the electronotes newsletter #111, it is hinted that these can be used to make a simple VCA. My very naive approach has been to just copy down the arrangement of NMOS and PMOS shown on the CD4009 datasheet as shown, without tweaking any parameters or selecting "pick new transistor". The circuit I am trying to simulate seems to qualitatively do what it is supposed to after some tweaking, but with the RC values and and supply voltage as shown in the original schematic, it does not achieve nearly the performance claimed. I am wondering if there is any way to select NMOS and PMOS parameters to improve my simulation's accuracy to the actual CD4009. Any help is much appreciated! see files: Eli_R_CD4009_VCA_Question.asc?and photo album Eli_R_CD4009_VCA_Question datasheet: [Moderator's note:? The original Subject said "CD4007", but the body of the message refers only to "CD4009".? I have modified the Subject line to suggest the CD4009.]
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Re: Crystal oscillator oscillation startup
?
Note : The oscillation amplitude is a bit too small during stable phase, not sure how to fix it properly yet.
?
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Re: Single-phase H-bridge inverter circuit
There are a number of ways to skin that cat.
In case of P and N FET design it may be possible to use high voltage BJT? to drive the upper half of the bridge.
In case of N channel FET upper half there are a few ways to drive the gate source junction.
The bot strap charge pump driver, a small low power isolated DC to DC converter in conjunction with an opto coupler for high speed operation limited by opto coupler performance.
A similar approach using a photo voltaic coupler good for low speed gate drive. Drive capability affected by gate source capacitance. ( see Panasonic's APV2111VY for example)
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Re: Pease tuneable MFB band-pass filter
There is another single pot tunable band pass network called Hall’s network.
it can tune over a decade. The commercial worked example is used in the general radio model 1232a tuned amplifier/null detector. It is a different circuit than Pease’s.
Jeff Furman AD6MX
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Re: Pease tuneable MFB band-pass filter
That was the undeliberated mistake.
On 2025-05-11 17:32, Jerry Lee Marcel
via groups.io wrote:
Now, is really the
output where it's on your schemo? I would put it at the opamp's
output. There the amplitude is constant.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
Re: Pease tuneable MFB band-pass filter
On Sun, May 11, 2025 at 06:22 PM, John Woodgate wrote:
The bandwidth is constant, so the Q varies with frequency.
Ok, I understand the misunderstanding. For me BW is always relative (octave or decade)
It is interesting to regard it as a bridged-T.
Now, is really the output where it's on your schemo? I would put it at the opamp's output. There the amplitude is constant.
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Re: Pease tuneable MFB band-pass filter
Thanks: that's why a search for bandpass'
failed.
On 2025-05-11 16:32, Mike Fraser wrote:
John,
The article is listed here.
.
NOTE: THE ARTICLE HAS THE TITLE WRONG.
It is a bandpass circuit.
Mike
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
Re: Pease tuneable MFB band-pass filter
DOH! Thanks, Mike.
On 2025-05-11 16:29, Mike Fraser wrote:
John,
Your schematic has the net "OUT" connected to the junction of
R2 and C2.
Move "OUT" to the output pin of U1.
Mike
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
Re: Pease tuneable MFB band-pass filter
On Sun, May 11, 2025 at 04:21 PM, John Woodgate wrote:
I have uploaded the above as a .ZIP. According to Bob Pease, the gain at the peak should be close to 34 dB, independent of the tuned frequency.
Then he must hav ereferred to a different circuit, maybe one with two variable elements, as used in the George Massenburg parametric EQ.
I don't get either of those results using version 24.1.8.
Neither do I.
However, the bandwidth is fairly constant with frequency, as predicted.
That's not what I see. I see the BW narrowing a
I can't believe Bob Pease reported the performance in error.
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Re: Pease tuneable MFB band-pass filter
The bandwidth is constant, so the Q varies
with frequency. I agree that the tuning range is restricted if
R2 isn't varied over a very wide range, because the peak
frequency is proportional to sqrt(R2).
It is interesting to regard it as a bridged-T.
On 2025-05-11 16:24, Jerry Lee Marcel
via groups.io wrote:
This circuit is basically an inverter with a bridged-T in the
feedback. Since it has only one variable element, the amplitude
of the peak and the BW (some say "Q") vary. Its usage is usually
reserved for applications where the tuning range is restricted.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
Re: Pease tuneable MFB band-pass filter
Gain being dependent only on the ratio of R3/R1 would depend on having enough gain-bandwidth in the opamp.
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John Woodgate
Tony Casey
Roy McCammon