"Anthony Fremont" schrieb im Newsbeitrag
...
Helmut Sennewald wrote:
Hello Anthony,

1.
Please set the following option to sitch off data
reduction/compression in the result file..

.options plotwinsize=0

2.
You have to set a small maximum timestep in the .TRAN line too.
Maybe a value of 0.01*Period of oscillation if you hunt for very low
distortion.


Can you send me your file (.asc-file and model-file?) to check it?

In alt.binaries.schematics.electronic I have posted the schematic, the
asc-file and an oscilloscope screen shot from an actual circuit. Here is
the asc-file contents:


Hello Anthony,

The large capacitance of C1 (10nF) has caused an interrupted oscillation.
Please change its value to 1000p and the oscillator will work as expected.
I have also added MEASURE-commands to measure the frequency.
View - SPICE Error Log

Another method is using the FFT in the waveform viewer.

Best regards,
Helmut

Save as "osc1.asc".

Version 4
SHEET 1 880 708
WIRE -688 -96 -784 -96
WIRE -576 -96 -688 -96
WIRE -304 -96 -576 -96
WIRE -784 -64 -784 -96
WIRE -688 -64 -688 -96
WIRE -576 -16 -576 -96
WIRE -304 32 -304 -96
WIRE -784 48 -784 16
WIRE -688 48 -688 0
WIRE -576 80 -576 64
WIRE -480 80 -576 80
WIRE -432 80 -480 80
WIRE -368 80 -432 80
WIRE -576 128 -576 80
WIRE -432 144 -432 80
WIRE -576 240 -576 208
WIRE -432 240 -432 208
WIRE -304 240 -304 128
WIRE -304 240 -432 240
WIRE -240 240 -304 240
WIRE -160 240 -240 240
WIRE -64 240 -96 240
WIRE -32 240 -64 240
WIRE -576 272 -576 240
WIRE -432 272 -432 240
WIRE -32 272 -32 240
WIRE -304 288 -304 240
WIRE -32 368 -32 352
WIRE -576 384 -576 336
WIRE -432 384 -432 336
WIRE -432 384 -576 384
WIRE -304 384 -304 368
WIRE -304 384 -432 384
WIRE -432 416 -432 384
FLAG -784 48 0
FLAG -432 416 0
FLAG -688 48 0
FLAG -32 368 0
FLAG -64 240 out
FLAG -240 240 e
FLAG -480 80 b
FLAG -576 240 lc
SYMBOL voltage -784 -80 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 5.8
SYMBOL res -592 -32 R0
SYMATTR InstName R3
SYMATTR Value 100k
SYMBOL npn -368 32 R0
SYMATTR InstName Q3
SYMATTR Value 2N3904
SYMBOL cap -448 144 R0
SYMATTR InstName C1
SYMATTR Value 1000p
SYMBOL res -320 272 R0
SYMATTR InstName R7
SYMATTR Value 1k
SYMBOL cap -448 272 R0
SYMATTR InstName C2
SYMATTR Value 500p
SYMBOL ind -592 112 R0
WINDOW 39 36 108 Left 0
SYMATTR InstName L1
SYMATTR Value 20µ
SYMATTR SpiceLine Rser=.1
SYMBOL cap -592 272 R0
SYMATTR InstName C3
SYMATTR Value 200p
SYMBOL cap -96 224 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C4
SYMATTR Value 270p
SYMBOL cap -704 -64 R0
SYMATTR InstName C5
SYMATTR Value 10µ
SYMBOL res -48 256 R0
SYMATTR InstName R2
SYMATTR Value 100k
TEXT -824 -152 Left 0 !.tran 0 200uS 0 4n
TEXT -824 -184 Left 0 !.options plotwinsize=0
TEXT -816 472 Left 0 !.measure tran t1 FIND time WHEN V(out)=0 TD=90u RISE=1
TEXT -816 504 Left 0 !.measure tran t2 FIND time WHEN V(out)=0 TD=90u
RISE=101
TEXT -816 536 Left 0 !.measure tran f0 PARAM 100/(t2-t1)
TEXT -816 576 Left 0 ;View - SPICE Error Log \nfor the measured frequency
TEXT -520 -184 Left 0 ;C1 changed to 1000p!

Helmut Sennewald wrote:
"Anthony Fremont" schrieb im Newsbeitrag
...
Helmut Sennewald wrote:
Hello Anthony,

1.
Please set the following option to sitch off data
reduction/compression in the result file..

.options plotwinsize=0

2.
You have to set a small maximum timestep in the .TRAN line too.
Maybe a value of 0.01*Period of oscillation if you hunt for very low
distortion.


Can you send me your file (.asc-file and model-file?) to check it?

In alt.binaries.schematics.electronic I have posted the schematic,
the asc-file and an oscilloscope screen shot from an actual circuit.
Here is the asc-file contents:


Hello Anthony,

The large capacitance of C1 (10nF) has caused an interrupted
oscillation. Please change its value to 1000p and the oscillator will
work as expected. I have also added MEASURE-commands to measure the
frequency. View - SPICE Error Log

Another method is using the FFT in the waveform viewer.

Best regards,
Helmut

Save as "osc1.asc".

Version 4
SHEET 1 880 708
WIRE -688 -96 -784 -96
WIRE -576 -96 -688 -96
WIRE -304 -96 -576 -96
WIRE -784 -64 -784 -96
WIRE -688 -64 -688 -96
WIRE -576 -16 -576 -96
WIRE -304 32 -304 -96
WIRE -784 48 -784 16
WIRE -688 48 -688 0
WIRE -576 80 -576 64
WIRE -480 80 -576 80
WIRE -432 80 -480 80
WIRE -368 80 -432 80
WIRE -576 128 -576 80
WIRE -432 144 -432 80
WIRE -576 240 -576 208
WIRE -432 240 -432 208
WIRE -304 240 -304 128
WIRE -304 240 -432 240
WIRE -240 240 -304 240
WIRE -160 240 -240 240
WIRE -64 240 -96 240
WIRE -32 240 -64 240
WIRE -576 272 -576 240
WIRE -432 272 -432 240
WIRE -32 272 -32 240
WIRE -304 288 -304 240
WIRE -32 368 -32 352
WIRE -576 384 -576 336
WIRE -432 384 -432 336
WIRE -432 384 -576 384
WIRE -304 384 -304 368
WIRE -304 384 -432 384
WIRE -432 416 -432 384
FLAG -784 48 0
FLAG -432 416 0
FLAG -688 48 0
FLAG -32 368 0
FLAG -64 240 out
FLAG -240 240 e
FLAG -480 80 b
FLAG -576 240 lc
SYMBOL voltage -784 -80 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 5.8
SYMBOL res -592 -32 R0
SYMATTR InstName R3
SYMATTR Value 100k
SYMBOL npn -368 32 R0
SYMATTR InstName Q3
SYMATTR Value 2N3904
SYMBOL cap -448 144 R0
SYMATTR InstName C1
SYMATTR Value 1000p
SYMBOL res -320 272 R0
SYMATTR InstName R7
SYMATTR Value 1k
SYMBOL cap -448 272 R0
SYMATTR InstName C2
SYMATTR Value 500p
SYMBOL ind -592 112 R0
WINDOW 39 36 108 Left 0
SYMATTR InstName L1
SYMATTR Value 20µ
SYMATTR SpiceLine Rser=.1
SYMBOL cap -592 272 R0
SYMATTR InstName C3
SYMATTR Value 200p
SYMBOL cap -96 224 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C4
SYMATTR Value 270p
SYMBOL cap -704 -64 R0
SYMATTR InstName C5
SYMATTR Value 10µ
SYMBOL res -48 256 R0
SYMATTR InstName R2
SYMATTR Value 100k
TEXT -824 -152 Left 0 !.tran 0 200uS 0 4n
TEXT -824 -184 Left 0 !.options plotwinsize=0
TEXT -816 472 Left 0 !.measure tran t1 FIND time WHEN V(out)=0 TD=90u
RISE=1 TEXT -816 504 Left 0 !.measure tran t2 FIND time WHEN V(out)=0
TD=90u RISE=101
TEXT -816 536 Left 0 !.measure tran f0 PARAM 100/(t2-t1)
TEXT -816 576 Left 0 ;View - SPICE Error Log \nfor the measured
frequency TEXT -520 -184 Left 0 ;C1 changed to 1000p!

Thank you very much. :-) I have now switched to using an MPF102 JFET
instead of the bipolar and much less capacitance for C1 (now 470pF). I only
get a 2V peak to peak signal out now, but it's quite nice looking.

Anthony Fremont wrote:
Pictures available in ABSE

The top trace (yellow) is taken between C4 and R2. The bottom trace (cyan)
is taken at the base of the transistor. There is a switchercad file, but
the simulation will show allot of distortion that really isn't present in
the prototype circuit, because of lots of circuit capactance I suspect. R1
was something I was playing with to try and tame the voltage across L1/C3
being applied to the base.


Hello all,

I was tinkering with this LC oscillator (Colpitts/Clapp) this weekend. I
arrived at the values of C1 and C2 empirically after starting with a crystal
oscillator circuit. The values in the original circuit created a horrid
waveform that looked allot like the simulation. After much tinkering around
and simulating, I come to the conclusion that getting a perfect waveform is
nearly impossible, especially with big swing. It seems that the transistor
likes to take a bite out of the right half of the peak of the wave.

What is the secret to beautiful waveforms? Do I need another LC resonator
on the output to fix it up? I mean, I'm getting a pretty nice wave now, but
there is still some distortion that you can just see at the top of the peaks
on the yellow trace.

How do you control the peak voltages of an LC resonattor without mangling
the waveform? The waveform at the junction of L1/C3 is of course quite
beautiful, how do I get it from there to the output? ;-)

I realize that I will need a buffer stage(s) before I can make any real use
of the signal, but I want the input to the buffer to be as perfect as
possible.

Thanks :-)



The secret to a beautiful waveform is -- you usually don't need it
straight from the oscillator.

There are a lot of things that you want out of an LC oscillator. Low
phase noise, frequency stability, consistently strong oscillation, pure
tone, etc. Of these, the only two that you can't clean up later in the
following amplifier chain is low phase noise and frequency stability.
Concentrate on those, & don't sweat the nice waveform.

Frequency stability and phase noise performance are often achieved by
intentionally designing the amplifier so the active element operates in
class C, without ever going into voltage saturation. This keeps it's
drain (or collector) impedance high, yet delivers a large voltage swing
to the gate (or base) to keep phase noise low. It also gives you a more
or less consistent standing voltage in the tank, which helps the design
of the following buffer stages.

If you absolutely positively must tap the World's Most Beautiful Sine
Wave off of the oscillator section, consider a parallel-tuned tank
that's loosely coupled to the active element. Then loosely couple your
output tap to that -- it's your best chance.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott wrote:

The secret to a beautiful waveform is -- you usually don't need it
straight from the oscillator.

Okay..

There are a lot of things that you want out of an LC oscillator. Low
phase noise, frequency stability, consistently strong oscillation,
pure tone, etc. Of these, the only two that you can't clean up later
in the following amplifier chain is low phase noise and frequency
stability. Concentrate on those, & don't sweat the nice waveform.

Okay, that certainly explains why all the sample circuits I find don't
expend any great effort at creaing a nice sine wave, and none at explaining
why. What you say certainly makes sense, especially if there are no really
negative consequences of having the oscillator make a "less than perfectly
shaped" wave.

Frequency stability and phase noise performance are often achieved by
intentionally designing the amplifier so the active element operates
in class C, without ever going into voltage saturation. This keeps
it's drain (or collector) impedance high, yet delivers a large
voltage swing to the gate (or base) to keep phase noise low. It also
gives you a more or less consistent standing voltage in the tank,
which helps the design of the following buffer stages.

If you absolutely positively must tap the World's Most Beautiful Sine
Wave off of the oscillator section, consider a parallel-tuned tank
that's loosely coupled to the active element. Then loosely couple
your output tap to that -- it's your best chance.

Ok, thanks for the information. :-) I did allot of googling but found
nothing that explained it like this. I was thinking of building a little
single conversion superhet WWV receiver for 10MHz, if I continue with that
I'll just concentrate on cleaning it up in another stage.

Some material I read suggested keeping Xl of L1 at ~300Ohms, the series Xc
(C3) at ~200Ohms and Xc of C1/C2 at 45Ohms. Do you have any thoughts on
that? Right now I have way too much inductance for 3.5MHz by that theory,
and judging from other circuits I've seen. 10uH seems to be the going thing
for around 4MHz?

Anthony Fremont wrote:

Tim Wescott wrote:


The secret to a beautiful waveform is -- you usually don't need it
straight from the oscillator.


Okay..


There are a lot of things that you want out of an LC oscillator. Low
phase noise, frequency stability, consistently strong oscillation,
pure tone, etc. Of these, the only two that you can't clean up later
in the following amplifier chain is low phase noise and frequency
stability. Concentrate on those, & don't sweat the nice waveform.


Okay, that certainly explains why all the sample circuits I find don't
expend any great effort at creaing a nice sine wave, and none at explaining
why. What you say certainly makes sense, especially if there are no really
negative consequences of having the oscillator make a "less than perfectly
shaped" wave.


Frequency stability and phase noise performance are often achieved by
intentionally designing the amplifier so the active element operates
in class C, without ever going into voltage saturation. This keeps
it's drain (or collector) impedance high, yet delivers a large
voltage swing to the gate (or base) to keep phase noise low. It also
gives you a more or less consistent standing voltage in the tank,
which helps the design of the following buffer stages.

If you absolutely positively must tap the World's Most Beautiful Sine
Wave off of the oscillator section, consider a parallel-tuned tank
that's loosely coupled to the active element. Then loosely couple
your output tap to that -- it's your best chance.


Ok, thanks for the information. :-) I did allot of googling but found
nothing that explained it like this. I was thinking of building a little
single conversion superhet WWV receiver for 10MHz, if I continue with that
I'll just concentrate on cleaning it up in another stage.

Some material I read suggested keeping Xl of L1 at ~300Ohms, the series Xc
(C3) at ~200Ohms and Xc of C1/C2 at 45Ohms. Do you have any thoughts on
that? Right now I have way too much inductance for 3.5MHz by that theory,
and judging from other circuits I've seen. 10uH seems to be the going thing
for around 4MHz?


That sounds more or less right. With a Clapp oscillator the main tank
is isolated by the series cap, so more of the energy is kept in the coil
and C3, and less of it shows up in C1, C2, and the transistor.

If you're driving a balanced mixer you want to have an LO signal that
doesn't have much even-harmonic (2nd, 4th, etc.) energy in it, but for a
casual receiver that's the least of your worries. Since you're
operating at a fixed frequency it may be a good idea to just feed the
oscillator output into a single-tuned resonant circuit to clean it up,
then send it on to the mixer.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott wrote:
Anthony Fremont wrote:

Some material I read suggested keeping Xl of L1 at ~300Ohms, the
series Xc (C3) at ~200Ohms and Xc of C1/C2 at 45Ohms. Do you have
any thoughts on that? Right now I have way too much inductance for
3.5MHz by that theory, and judging from other circuits I've seen.
10uH seems to be the going thing for around 4MHz?


That sounds more or less right. With a Clapp oscillator the main tank
is isolated by the series cap, so more of the energy is kept in the
coil and C3, and less of it shows up in C1, C2, and the transistor.

If you're driving a balanced mixer you want to have an LO signal that
doesn't have much even-harmonic (2nd, 4th, etc.) energy in it, but
for a casual receiver that's the least of your worries. Since you're
operating at a fixed frequency it may be a good idea to just feed the
oscillator output into a single-tuned resonant circuit to clean it up,
then send it on to the mixer.

Ok, I've now put in an MPF102 and changed R3 to a pull-down. I lowered C1
to 470pF and I get a nifty 2V p-p sine wave on the output. It really tamed
the tank circuit voltage down as well. Which brings up a question, with the
tank now completely DC blocked from Vcc and Vss, where does it get it's
energy. I assume that it must come thru the gate. How does that happen?
:-? My circuit is much like Figure 1 here, without the diode though:
http://www.electronics-tutorials.com...scillators.htm

Anthony Fremont wrote:
Tim Wescott wrote:

Anthony Fremont wrote:


Some material I read suggested keeping Xl of L1 at ~300Ohms, the
series Xc (C3) at ~200Ohms and Xc of C1/C2 at 45Ohms. Do you have
any thoughts on that? Right now I have way too much inductance for
3.5MHz by that theory, and judging from other circuits I've seen.
10uH seems to be the going thing for around 4MHz?



That sounds more or less right. With a Clapp oscillator the main tank
is isolated by the series cap, so more of the energy is kept in the
coil and C3, and less of it shows up in C1, C2, and the transistor.

If you're driving a balanced mixer you want to have an LO signal that
doesn't have much even-harmonic (2nd, 4th, etc.) energy in it, but
for a casual receiver that's the least of your worries. Since you're
operating at a fixed frequency it may be a good idea to just feed the
oscillator output into a single-tuned resonant circuit to clean it up,
then send it on to the mixer.


Ok, I've now put in an MPF102 and changed R3 to a pull-down. I lowered C1
to 470pF and I get a nifty 2V p-p sine wave on the output. It really tamed
the tank circuit voltage down as well. Which brings up a question, with the
tank now completely DC blocked from Vcc and Vss, where does it get it's
energy. I assume that it must come thru the gate. How does that happen?
:-? My circuit is much like Figure 1 here, without the diode though:
http://www.electronics-tutorials.com...scillators.htm


It comes from the source, through the coupling capacitors -- Cfb-a and
Cfb-b in your link.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

Anthony Fremont wrote:

Pictures available in ABSE

The top trace (yellow) is taken between C4 and R2. The bottom trace
(cyan)
is taken at the base of the transistor. There is a switchercad file, but
the simulation will show allot of distortion that really isn't present in
the prototype circuit, because of lots of circuit capactance I suspect.
R1 was something I was playing with to try and tame the voltage across
L1/C3 being applied to the base.


Hello all,

I was tinkering with this LC oscillator (Colpitts/Clapp) this weekend. I
arrived at the values of C1 and C2 empirically after starting with a
crystal
oscillator circuit. The values in the original circuit created a horrid
waveform that looked allot like the simulation. After much tinkering
around and simulating, I come to the conclusion that getting a perfect
waveform is
nearly impossible, especially with big swing. It seems that the
transistor likes to take a bite out of the right half of the peak of the
wave.

What is the secret to beautiful waveforms? Do I need another LC resonator
on the output to fix it up? I mean, I'm getting a pretty nice wave now,
but there is still some distortion that you can just see at the top of the
peaks on the yellow trace.

How do you control the peak voltages of an LC resonattor without mangling
the waveform? The waveform at the junction of L1/C3 is of course quite
beautiful, how do I get it from there to the output? ;-)

I realize that I will need a buffer stage(s) before I can make any real
use of the signal, but I want the input to the buffer to be as perfect as
possible.

Thanks :-)

In some LC oscillators, the amplitude of the oscillation is controlled by a
feedback loop. For example, a rectifier can be used to create a DC voltage
proportional to the oscillation amplitude on the LC tank, and then an
op-amp can be used to compare the rectifier output signal to a reference
voltage. The output from the op-amp can be filtered and then used to
control the current in the oscillator core. It is difficult to do all of
this in a way that keeps the phase noise low, but given the right
simulation tools (e.g. SpectreRF which is rather expensive), good results
can be obtained. In particular, a well-defined oscillation amplitude can
help to keep the KVCO well controlled, which is useful in PLLs.

Chris

On Mar 19, 12:23 pm, "Anthony Fremont" wrote:
Pictures available in ABSE

The top trace (yellow) is taken between C4 and R2. The bottom trace (cyan)
is taken at the base of the transistor. There is a switchercad file, but
the simulation will show allot of distortion that really isn't present in
the prototype circuit, because of lots of circuit capactance I suspect. R1
was something I was playing with to try and tame the voltage across L1/C3
being applied to the base.

Hello all,

I was tinkering with this LC oscillator (Colpitts/Clapp) this weekend. I
arrived at the values of C1 and C2 empirically after starting with a crystal
oscillator circuit. The values in the original circuit created a horrid
waveform that looked allot like the simulation. After much tinkering around
and simulating, I come to the conclusion that getting a perfect waveform is
nearly impossible, especially with big swing. It seems that the transistor
likes to take a bite out of the right half of the peak of the wave.

What is the secret to beautiful waveforms? Do I need another LC resonator
on the output to fix it up? I mean, I'm getting a pretty nice wave now, but
there is still some distortion that you can just see at the top of the peaks
on the yellow trace.

How do you control the peak voltages of an LC resonattor without mangling
the waveform? The waveform at the junction of L1/C3 is of course quite
beautiful, how do I get it from there to the output? ;-)

Oscillators have to have gain greater than one at the frequency of
oscillation.

When turned on, the amplitude builds up until something in the circuit
cuts back the gain. In simple oscillators, that "something that cuts
back the gain" is almost always the active device saturating and
distorting its output.

The higher your gain, the more reliable the oscillator starting up,
but also the higher the distortion.

If you take the output not from the output of the active device, but
from a lightly-coupled tank, then you'll see something much more like
the sine wave you were expecting. This is what you see at the L1/C3
junction. But still you'll get lower distortion there if the active
device isn't driven so far into saturation/distortion. And by
definition you cannot suck much power out of the L1/C3 junction
without decreasing the Q of the tank and making distortion there too.

You can add a few more active devices and not only buffer things but
also put a fairly linear AGC in the loop. This still has distortion,
but this is done intentionally in a rectifier to derive the AGC
control voltage, which is then filtered. The intentional distortion
does not have to appear in the output!

Clever use of devices can make the AGC loop quite beautiful. Look at
the Wien Bridge or Meacham Bridge oscillators that use a light bulb in
the bridge to not only be the loop-control device but also do
filtering (thermal time constant of the filament).

Tim.

Tim Shoppa wrote:

Oscillators have to have gain greater than one at the frequency of
oscillation.

When turned on, the amplitude builds up until something in the circuit
cuts back the gain. In simple oscillators, that "something that cuts
back the gain" is almost always the active device saturating and
distorting its output.

The higher your gain, the more reliable the oscillator starting up,
but also the higher the distortion.

If you take the output not from the output of the active device, but
from a lightly-coupled tank, then you'll see something much more like
the sine wave you were expecting. This is what you see at the L1/C3
junction. But still you'll get lower distortion there if the active
device isn't driven so far into saturation/distortion. And by
definition you cannot suck much power out of the L1/C3 junction
without decreasing the Q of the tank and making distortion there too.

It seams reasonable that if I can look at the junction with a scope and the
wave looks good, I should be able to tap it with a secondary JFET without
destroying it. Yet I see no examples of that being done. I guess it's just
easier to accomplish the waveform repair by using a tank on the output of
the oscillator and not loading down the primary tank circuit.

You can add a few more active devices and not only buffer things but
also put a fairly linear AGC in the loop. This still has distortion,
but this is done intentionally in a rectifier to derive the AGC
control voltage, which is then filtered. The intentional distortion
does not have to appear in the output!

This sounds like what Chris Jones was talking about. Do you have a link so
I could check it out?

Clever use of devices can make the AGC loop quite beautiful. Look at
the Wien Bridge or Meacham Bridge oscillators that use a light bulb in
the bridge to not only be the loop-control device but also do
filtering (thermal time constant of the filament).

Clever stuff. :-)