Voltage controlled oscillator question

[Daku]

Could someone please clarify the following ?
Consider a LC-tank and a ring oscillator based voltage controlled
oscillator. In a LC-tank, the control voltage influences the
oscillation frequency - hence "voltage controlled oscillator". In a
ring oscillator based voltage controlled oscillator, the oscillation
frequency is independent of a control voltage. The control voltage
basically switches the inverters on and off. So how does one control
the oscillation frequency ??

 

[Phil Allison]

"Daku"

Could someone please clarify the following ?
Consider a LC-tank and a ring oscillator based voltage controlled
oscillator. In a LC-tank, the control voltage influences the
oscillation frequency - hence "voltage controlled oscillator". In a
ring oscillator based voltage controlled oscillator, the oscillation
frequency is independent of a control voltage. The control voltage
basically switches the inverters on and off. So how does one control
the oscillation frequency ??

** Ever heard of Google, you PITA time waster ??

http://en.wikipedia.org/wiki/Ring_oscillator

Yawnnnnnnnnnnnn....



...... Phil

 

[John O'Flaherty]

On Sun, 9 May 2010 23:30:32 -0700 (PDT), Daku <dakupoto@gmail.com>
wrote:

Could someone please clarify the following ?
Consider a LC-tank and a ring oscillator based voltage controlled
oscillator. In a LC-tank, the control voltage influences the
oscillation frequency - hence "voltage controlled oscillator". In a
ring oscillator based voltage controlled oscillator, the oscillation
frequency is independent of a control voltage. The control voltage
basically switches the inverters on and off. So how does one control
the oscillation frequency ??

Unless some other aspect than frequency is being controlled by the
control voltage (amplitude or phase or waveshape), your description is
contradictory. According to a google search, a "ring oscillator VCO"
is a string of inverting stages connected in a circle, whose frequency
of oscillation is changed by a control voltage that modifies
resistance or capacitance so as to change the delay. This could also
be called a "But...!" gate.

http://tinyurl.com/2564vxw

--
John

 

[Michael Black]

On Sun, 9 May 2010, Daku wrote:

Could someone please clarify the following ?
Consider a LC-tank and a ring oscillator based voltage controlled
oscillator. In a LC-tank, the control voltage influences the
oscillation frequency - hence "voltage controlled oscillator". In a
ring oscillator based voltage controlled oscillator, the oscillation
frequency is independent of a control voltage. The control voltage
basically switches the inverters on and off. So how does one control
the oscillation frequency ??

Lots of things can change frequency with voltage, some schemes work

better than others.

If you are really seeing a voltage variable ring oscillator (your
description almost sounds like it's merely a ring counter with a means
of turning it on and off, but that's not clear), there are various
things that might work.


For instance, for really cheap applications, or hobbyists playing around,
changing the voltage to the IC would change the frequency, though within a
limited range and it may impact on some other aspects of the oscillator.
But if you need a cheap and dirty VCO for some limited application, it
might work.

Another scheme is that by injecting a DC voltage into the right point, you
control the switching point of that stage, and that changes the frequency
of the ring counter.

Otherwise, you're back to changing the capacitor or resistor of the
ring counter to change frequency.

Note that one popular VCO is to use a 555 timer, and vary the voltage
on pin 5, the threshold level pin. That changes when the timer switches,
and thus allows for a limited variation of frequency by control voltage.
Similar schemes have been cooked up, though with such things one is
usually limited by how much you can vary the frequency, and it may
affect some other part of the oscillator. But again, if you only
need a small variation, it works and is simpler circuit wise than
a more complicated VCO.

Michael

 

[Tim Wescott]

Daku wrote:

Could someone please clarify the following ?
Consider a LC-tank and a ring oscillator based voltage controlled
oscillator. In a LC-tank, the control voltage influences the
oscillation frequency - hence "voltage controlled oscillator".

In general, LC tanks don't have control voltage ports, so their
resonance frequency can't be controlled by a voltage. In VCO usage,
there's a voltage-controlled part -- nearly always a varactor diode,
although there are other ways to control the frequency of an LC
oscillator, if you're feeling perverse.

In a
ring oscillator based voltage controlled oscillator, the oscillation
frequency is independent of a control voltage. The control voltage
basically switches the inverters on and off. So how does one control
the oscillation frequency ??

Like the LC oscillator, a ring oscillator is not an inherently voltage
controlled device. Like the LC oscillator, if one wants to base a VCO
on a ring oscillator, one must modify one's oscillator to respond to a
control voltage.

There must be a real question buried in here, but you've worked so hard
to abstract your question from what you're doing that you've lost the
sense of it. Try again, starting with what you want to _do_ -- even if
it's to understand why professor X and university Y has published an
article about phase locked loops using ring oscillators.

With a sensible question, perhaps we can make sensible answers.

With a more detailed but still mangled question, perhaps we can help you
make a sensible question.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

[George Herold]

On May 10, 11:52 am, Tim Wescott <t...@seemywebsite.now> wrote:

Daku wrote:
Could someone please clarify the following ?
Consider a LC-tank and a ring oscillator based voltage controlled
oscillator. In a LC-tank, the control voltage influences the
oscillation frequency - hence "voltage controlled oscillator".

In general, LC tanks don't have control voltage ports, so their
resonance frequency can't be controlled by a voltage.  In VCO usage,
there's a voltage-controlled part -- nearly always a varactor diode,
although there are other ways to control the frequency of an LC
oscillator, if you're feeling perverse.

In a
ring oscillator based  voltage controlled oscillator, the oscillation
frequency is independent of a control voltage.  The control voltage
basically switches the inverters on and off. So how does one control
the oscillation frequency ??

Like the LC oscillator, a ring oscillator is not an inherently voltage
controlled device.  Like the LC oscillator, if one wants to base a VCO
on a ring oscillator, one must modify one's oscillator to respond to a
control voltage.

Hey, does CMOS have a time delay that depends on the supply voltage?
(It seems like it might.. or you could add some R's between stages.)
Then you could control the frequency somewhat by changing the supply
voltage.

George H.

There must be a real question buried in here, but you've worked so hard
to abstract your question from what you're doing that you've lost the
sense of it.  Try again, starting with what you want to _do_ -- even if
it's to understand why professor X and university Y has published an
article about phase locked loops using ring oscillators.

With a sensible question, perhaps we can make sensible answers.

With a more detailed but still mangled question, perhaps we can help you
make a sensible question.

--
Tim Wescott
Control system and signal processing consultingwww.wescottdesign.com

 

[Tim Wescott]

Daku wrote:

Thanks for the feedback. My question, basically is:
How do I control the oscillation frequency of a ring oscillator based
voltage
controlled oscillator? I have created SPICE code for both varactor-LC
tank
and ring oscillator VCOs, and while I am testing the ring oscillator
based
code, I am not sure what parameters I need to tweak to see the
oscillation
frequency change.

On May 10, 8:52 pm, Tim Wescott <t...@seemywebsite.now> wrote:
In general, LC tanks don't have control voltage ports, so their
resonance frequency can't be controlled by a voltage. In VCO usage,
there's a voltage-controlled part -- nearly always a varactor diode,
although there are other ways to control the frequency of an LC
oscillator, if you're feeling perverse.
Yes, as I said before, I do have a working SPICE model of a varactor
-LC VCO.
In a
ring oscillator based voltage controlled oscillator, the oscillation
frequency is independent of a control voltage. The control voltage
basically switches the inverters on and off. So how does one control
the oscillation frequency ??
Like the LC oscillator, a ring oscillator is not an inherently voltage
controlled device. Like the LC oscillator, if one wants to base a VCO
on a ring oscillator, one must modify one's oscillator to respond to a
control voltage.

Exactly. Consider the simplest ring oscillator consisting of 3 CMOS
inverters, wirh a PMOS and NMOS at the top and bottom of each, so
that each of the PMOS acts a pull-up and the NMOS as the pull-down.
Each of the pull-up PMOS have their gates tied, and each of the NMOS
have their gates tied as well. By applying an appropriate gate
voltage, I
can pull down each of the inverters and start the ring oscillator to
oscillate.
Now if the voltage applied to each of the NMOS is below the NMOS
threshold, there is no oscillation. However, once the start the
oscillator,
how do I vary the frequency ??

There must be a real question buried in here, but you've worked so hard
to abstract your question from what you're doing that you've lost the
sense of it. Try again, starting with what you want to _do_ -- even if
it's to understand why professor X and university Y has published an
article about phase locked loops using ring oscillators.

With a sensible question, perhaps we can make sensible answers.

With a more detailed but still mangled question, perhaps we can help you
make a sensible question.

If you don't have any clue how to vary the frequency of your ring
oscillator, why do you want to use one?

Have you searched the literature? Have you Googled?

As far as I know a ring oscillator is a really crappy oscillator that
semiconductor companies build for bragging rights about how fast their
new processes go. To what practical use are you planning on putting
your ring oscillator, why won't something like an RC oscillator work,
and why would you want to control the speed of a ring oscillator if all
they're good for is going fast?

If you have no clue, if you can't find the answer from colleagues or
fellow students, and if you really do need to make the thing work -- how
about "bleeder" FETS at each stage, to lightly pull the node up or down?
You'll kill gain, which will make the thing not want to oscillate, but
you'll also slow it down.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

[Daku]

Thanks for the feedback. My question, basically is:
How do I control the oscillation frequency of a ring oscillator based
voltage
controlled oscillator? I have created SPICE code for both varactor-LC
tank
and ring oscillator VCOs, and while I am testing the ring oscillator
based
code, I am not sure what parameters I need to tweak to see the
oscillation
frequency change.

On May 10, 8:52 pm, Tim Wescott <t...@seemywebsite.now> wrote:

In general, LC tanks don't have control voltage ports, so their
resonance frequency can't be controlled by a voltage. In VCO usage,
there's a voltage-controlled part -- nearly always a varactor diode,
although there are other ways to control the frequency of an LC
oscillator, if you're feeling perverse.
Yes, as I said before, I do have a working SPICE model of a varactor

-LC VCO.

In a
ring oscillator based voltage controlled oscillator, the oscillation
frequency is independent of a control voltage. The control voltage
basically switches the inverters on and off. So how does one control
the oscillation frequency ??

Like the LC oscillator, a ring oscillator is not an inherently voltage
controlled device. Like the LC oscillator, if one wants to base a VCO
on a ring oscillator, one must modify one's oscillator to respond to a
control voltage.
Exactly. Consider the simplest ring oscillator consisting of 3 CMOS

inverters, wirh a PMOS and NMOS at the top and bottom of each, so
that each of the PMOS acts a pull-up and the NMOS as the pull-down.
Each of the pull-up PMOS have their gates tied, and each of the NMOS
have their gates tied as well. By applying an appropriate gate
voltage, I
can pull down each of the inverters and start the ring oscillator to
oscillate.
Now if the voltage applied to each of the NMOS is below the NMOS
threshold, there is no oscillation. However, once the start the
oscillator,
how do I vary the frequency ??

There must be a real question buried in here, but you've worked so hard
to abstract your question from what you're doing that you've lost the
sense of it. Try again, starting with what you want to _do_ -- even if
it's to understand why professor X and university Y has published an
article about phase locked loops using ring oscillators.

With a sensible question, perhaps we can make sensible answers.

With a more detailed but still mangled question, perhaps we can help you
make a sensible question.

--
Tim Wescott
Control system and signal processing consultingwww.wescottdesign.com

 

[whit3rd]

On May 10, 9:37 am, George Herold <ggher...@gmail.com> wrote:

[on the subject of VCO circuitry]

Hey, does CMOS have a time delay that depends on the supply voltage?
(It seems like it might.. or you could add some R's between stages.)
Then you could control the frequency somewhat by changing the supply
voltage.

The output impedance of CMOS does depend on the power supply
voltage, of course, as well as on temperature and unit-to-unit
variations. This quality is better developed, IMHO, in OTA
(operational transconductance amplifier) circuits.
CMOS impedance can vary by a factor of six (3 to 18V range of
4000 series gates), but the old CA3080 was good for a factor
of 1000.

 

[John Fields]

On Mon, 10 May 2010 09:37:56 -0700 (PDT), George Herold
<ggherold@gmail.com> wrote:

Hey, does CMOS have a time delay that depends on the supply voltage?
(It seems like it might.. or you could add some R's between stages.)
Then you could control the frequency somewhat by changing the supply
voltage.

---
From TI's 1989 High Speed CMOS Logic Data Book:

news:t6piu55sqenrovms7k5fuhrl8m7666thng@4ax.com

 

[Daku]

Dear Sir,
I do not intend to use a ring oscillator based VCO.
However, as you have said below, literature search
shows a lot of people using the ring oscillator based
voltage controlled oscillator in phase locked loop
designs, which is sounds strange to me, since in a
phase locked loop, the VCO oscillation frequency
must be very sensitive to the input voltage level.
Maybe the ring oscillator is designed to oscillate
at the central frequency, but frequency variation is
difficult and tricky.

If you don't have any clue how to vary the frequency of your ring
oscillator, why do you want to use one?

Have you searched the literature? Have you Googled?

As far as I know a ring oscillator is a really crappy oscillator that
semiconductor companies build for bragging rights about how fast their
new processes go. To what practical use are you planning on putting
your ring oscillator, why won't something like an RC oscillator work,
and why would you want to control the speed of a ring oscillator if all
they're good for is going fast?

If you have no clue, if you can't find the answer from colleagues or
fellow students, and if you really do need to make the thing work -- how
about "bleeder" FETS at each stage, to lightly pull the node up or down?
You'll kill gain, which will make the thing not want to oscillate, but
you'll also slow it down.

--
Tim Wescott
Control system and signal processing consultingwww.wescottdesign.com

 

[John Fields]

On Tue, 11 May 2010 20:39:37 -0700 (PDT), Daku <dakupoto@gmail.com>
wrote:

Dear Sir,
I do not intend to use a ring oscillator based VCO.
However, as you have said below, literature search
shows a lot of people using the ring oscillator based
voltage controlled oscillator in phase locked loop
designs, which is sounds strange to me, since in a
phase locked loop, the VCO oscillation frequency
must be very sensitive to the input voltage level.
Maybe the ring oscillator is designed to oscillate
at the central frequency, but frequency variation is
difficult and tricky.

---
Please bottom post, or inline post when it's necessary for clarity.
Thank you.

As others have noted, your original post seems to indicate that you
don't have a really good grasp on what's required to change the
frequency of an oscillator as a function of an applied voltage.

For an LC tank, where:

1
f = -------------,
2pi sqrt LC

then either L or C must be varied as a function of voltage in order to
make f change.

In the old days it was done with a saturable reactor, where the DC
voltage on the control winding and the attendant current through it
changed the reluctance of the core and, thererfore, the inductance
described by the secondary.

Today, afaik, it's done with varactors.

Comment?

 

[krw@att.bizzzzzzzzzzzz]

On Wed, 12 May 2010 19:09:42 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Tue, 11 May 2010 20:39:37 -0700 (PDT), Daku <dakupoto@gmail.com
wrote:

Dear Sir,
I do not intend to use a ring oscillator based VCO.
However, as you have said below, literature search
shows a lot of people using the ring oscillator based
voltage controlled oscillator in phase locked loop
designs, which is sounds strange to me, since in a
phase locked loop, the VCO oscillation frequency
must be very sensitive to the input voltage level.
Maybe the ring oscillator is designed to oscillate
at the central frequency, but frequency variation is
difficult and tricky.

---
Please bottom post, or inline post when it's necessary for clarity.
Thank you.

As others have noted, your original post seems to indicate that you
don't have a really good grasp on what's required to change the
frequency of an oscillator as a function of an applied voltage.

For an LC tank, where:

1
f = -------------,
2pi sqrt LC

then either L or C must be varied as a function of voltage in order to
make f change.

In the old days it was done with a saturable reactor, where the DC
voltage on the control winding and the attendant current through it
changed the reluctance of the core and, thererfore, the inductance
described by the secondary.

Today, afaik, it's done with varactors.

Comment?

It can be done with ring oscillators, too. Gate delay isn't a strong function
of Vcc, though so it's not done often. DLLs generally use a mux to select the
number of gates in the ring.

 

[Michael Black]

On Wed, 12 May 2010, Daku wrote:

On May 13, 5:09 am, John Fields <jfie...@austininstruments.com> wrote:

---
Please bottom post, or inline post when it's necessary for clarity.
Thank you.

As others have noted, your original post seems to indicate that you
don't have a really good grasp on what's required to change the
frequency of an oscillator as a function of an applied voltage.

For an LC tank, where:

1
f = -------------,
2pi sqrt LC

then either L or C must be varied as a function of voltage in order to
make f change.

In the old days it was done with a saturable reactor, where the DC
voltage on the control winding and the attendant current through it
changed the reluctance of the core and, thererfore, the inductance
described by the secondary.

Today, afaik, it's done with varactors.

Comment?

Dear Sir,
I am fully aware of the LC-tank circuit, and that a varactor needs to
be
added in the tank to get the voltage control. However, a simple
literature
search on voltage controlled oscillators indicates that a large number
of
designs are based on the CMOS ring oscillator. As one of other posters
noted before (and I fully agree with him) that it is difficult to
dynamically
control the oscillation frequency of the CMOS ring oscillator - this
frequency
is based on the characteristics of the MOSFETs in the inverters of
the
ring oscillator. Given that, how are these ring oscillator based
designs
being labelled "voltage controlled" since the voltage control merely
switches the oscillations on and off, NOT control the frequency as in
a
LC tank.

Show us a sample circuit, and we'll explain it. Until we actually

see what you are talking about, then "how" can only be conjecture.
Show us a sample circuit, and then that circuit can be explained.

Michael

 

[Daku]

On May 13, 5:09 am, John Fields <jfie...@austininstruments.com> wrote:

---
Please bottom post, or inline post when it's necessary for clarity.
Thank you.

As others have noted, your original post seems to indicate that you
don't have a really good grasp on what's required to change the
frequency of an oscillator as a function of an applied voltage.

For an LC tank, where:

1
f = -------------,
2pi sqrt LC

then either L or C must be varied as a function of voltage in order to
make f change.

In the old days it was done with a saturable reactor, where the DC
voltage on the control winding and the attendant current through it
changed the reluctance of the core and, thererfore, the inductance
described by the secondary.

Today, afaik, it's done with varactors.

Comment?

Dear Sir,
I am fully aware of the LC-tank circuit, and that a varactor needs to
be
added in the tank to get the voltage control. However, a simple
literature
search on voltage controlled oscillators indicates that a large number
of
designs are based on the CMOS ring oscillator. As one of other posters
noted before (and I fully agree with him) that it is difficult to
dynamically
control the oscillation frequency of the CMOS ring oscillator - this
frequency
is based on the characteristics of the MOSFETs in the inverters of
the
ring oscillator. Given that, how are these ring oscillator based
designs
being labelled "voltage controlled" since the voltage control merely
switches the oscillations on and off, NOT control the frequency as in
a
LC tank.

 

[Jasen Betts]

On 2010-05-13, Daku <dakupoto@gmail.com> wrote:

However, a simple literature
search on voltage controlled oscillators indicates that a large number
of designs are based on the CMOS ring oscillator. As one of other posters
noted before (and I fully agree with him) that it is difficult to
dynamically control the oscillation frequency of the CMOS ring oscillator
- this frequency is based on the characteristics of the MOSFETs in the
inverters of
the ring oscillator. Given that, how are these ring oscillator based
designs
being labelled "voltage controlled" since the voltage control merely
switches the oscillations on and off,

No, it doesn't


also feedback helps things.


--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

 

[John Fields]

On Wed, 12 May 2010 22:07:32 -0500, "krw@att.bizzzzzzzzzzzz"
<krw@att.bizzzzzzzzzzzz> wrote:

On Wed, 12 May 2010 19:09:42 -0500, John Fields
jfields@austininstruments.com> wrote:

On Tue, 11 May 2010 20:39:37 -0700 (PDT), Daku <dakupoto@gmail.com
wrote:

Dear Sir,
I do not intend to use a ring oscillator based VCO.
However, as you have said below, literature search
shows a lot of people using the ring oscillator based
voltage controlled oscillator in phase locked loop
designs, which is sounds strange to me, since in a
phase locked loop, the VCO oscillation frequency
must be very sensitive to the input voltage level.
Maybe the ring oscillator is designed to oscillate
at the central frequency, but frequency variation is
difficult and tricky.

---
Please bottom post, or inline post when it's necessary for clarity.
Thank you.

As others have noted, your original post seems to indicate that you
don't have a really good grasp on what's required to change the
frequency of an oscillator as a function of an applied voltage.

For an LC tank, where:

1
f = -------------,
2pi sqrt LC

then either L or C must be varied as a function of voltage in order to
make f change.

In the old days it was done with a saturable reactor, where the DC
voltage on the control winding and the attendant current through it
changed the reluctance of the core and, thererfore, the inductance
described by the secondary.

Today, afaik, it's done with varactors.

Comment?

It can be done with ring oscillators, too. Gate delay isn't a strong function
of Vcc, though so it's not done often. DLLs generally use a mux to select the
number of gates in the ring.

---
Actually, the change in delay is quite pronounced, as shown by:

news:t6piu55sqenrovms7k5fuhrl8m7666thng@4ax.com

from TI's 1989 GMOS logic data book.

Also, for an HC00, tpd at 25C is 15ns max for Vcc = 6V, 18ns for 4.5V,
and 90ns for 2V.

 

[John Fields]

On Wed, 12 May 2010 20:07:26 -0700 (PDT), Daku <dakupoto@gmail.com>
wrote:

On May 13, 5:09 am, John Fields <jfie...@austininstruments.com> wrote:

---
Please bottom post, or inline post when it's necessary for clarity.
Thank you.

As others have noted, your original post seems to indicate that you
don't have a really good grasp on what's required to change the
frequency of an oscillator as a function of an applied voltage.

For an LC tank, where:

1
f = -------------,
2pi sqrt LC

then either L or C must be varied as a function of voltage in order to
make f change.

In the old days it was done with a saturable reactor, where the DC
voltage on the control winding and the attendant current through it
changed the reluctance of the core and, thererfore, the inductance
described by the secondary.

Today, afaik, it's done with varactors.

Comment?

Dear Sir,
I am fully aware of the LC-tank circuit, and that a varactor needs to
be added in the tank to get the voltage control. However, a simple
literature search on voltage controlled oscillators indicates that a large number
of designs are based on the CMOS ring oscillator.

---
After doing a cursory search for "ring counter VCO", such seems notv
to be the case.

Can you cite the links you found, please?
---

As one of other posters
noted before (and I fully agree with him) that it is difficult to
dynamically control the oscillation frequency of the CMOS ring oscillator - this
frequency is based on the characteristics of the MOSFETs in the inverters of
the ring oscillator. Given that, how are these ring oscillator based
designs being labelled "voltage controlled" since the voltage control merely
switches the oscillations on and off, NOT control the frequency as in
a LC tank.

---
That's not true, since if Vcc is varied, as shown in:

news:t6piu55sqenrovms7k5fuhrl8m7666thng@4ax.com

Then a VCO can be readily fashioned from HCMOS logic gates by
exploiting the fact that the gate delay varies over quite a wide range
(about 6:1) with Vcc changing from 2 to 6V.

 

[krw@att.bizzzzzzzzzzzz]

On Thu, 13 May 2010 08:50:37 -0500, John Fields
<jfields@austininstruments.com> wrote:

On Wed, 12 May 2010 22:07:32 -0500, "krw@att.bizzzzzzzzzzzz"
krw@att.bizzzzzzzzzzzz> wrote:

On Wed, 12 May 2010 19:09:42 -0500, John Fields
jfields@austininstruments.com> wrote:

On Tue, 11 May 2010 20:39:37 -0700 (PDT), Daku <dakupoto@gmail.com
wrote:

Dear Sir,
I do not intend to use a ring oscillator based VCO.
However, as you have said below, literature search
shows a lot of people using the ring oscillator based
voltage controlled oscillator in phase locked loop
designs, which is sounds strange to me, since in a
phase locked loop, the VCO oscillation frequency
must be very sensitive to the input voltage level.
Maybe the ring oscillator is designed to oscillate
at the central frequency, but frequency variation is
difficult and tricky.

---
Please bottom post, or inline post when it's necessary for clarity.
Thank you.

As others have noted, your original post seems to indicate that you
don't have a really good grasp on what's required to change the
frequency of an oscillator as a function of an applied voltage.

For an LC tank, where:

1
f = -------------,
2pi sqrt LC

then either L or C must be varied as a function of voltage in order to
make f change.

In the old days it was done with a saturable reactor, where the DC
voltage on the control winding and the attendant current through it
changed the reluctance of the core and, thererfore, the inductance
described by the secondary.

Today, afaik, it's done with varactors.

Comment?

It can be done with ring oscillators, too. Gate delay isn't a strong function
of Vcc, though so it's not done often. DLLs generally use a mux to select the
number of gates in the ring.

---
Actually, the change in delay is quite pronounced, as shown by:

news:t6piu55sqenrovms7k5fuhrl8m7666thng@4ax.com

from TI's 1989 GMOS logic data book.

Also, for an HC00, tpd at 25C is 15ns max for Vcc = 6V, 18ns for 4.5V,
and 90ns for 2V.

+/- 10% isn't very good for the capture ratio. The normal (lot-to-lot)
variation is likely much larger, making it more or less useless for a VCO.

 

[Phil Allison]

<krw@att.bizzzzzzzzzzzz>
John Fields

Also, for an HC00, tpd at 25C is 15ns max for Vcc = 6V, 18ns for 4.5V,
and 90ns for 2V.

+/- 10% isn't very good for the capture ratio.

** Learn to read dickhead.

The ratio is 6:1.




..... Phil