I need a design for 1MHz to 2MHz Voltage controlled oscillator for square wave which uses op-amp. Any help is appreciated...thank you
- posted
17 years ago
I need a design for 1MHz to 2MHz Voltage controlled oscillator for square wave which uses op-amp. Any help is appreciated...thank you
Just buy an MC4024... 3.5:1 tuning range
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
Have a look at
at page 9 fig 27 for the basic idea. The circuit is described as as a triangular wave generator, but in fact the left-hand amplifier is producing a square wave.
The LM101 won't do 1MHz to 2MHz, but nowadays you can buy faster parts.
The LM101 won't produce a well-defined square waveat the output of the left-hand amplifier, but an amplifier delivering a rail-to-rail output swing would do better. The
comes to mind, but it isn't fast enough for a 1-2MHz oscillator either.
There are a couple of ways of making the circuit into a voltage controlled oscillator, but since this appears to be a homework excercise, I won't go into them yet.
-- Bill Sloman, Nijmegen (but in Melbourne at the moment)
square wave suggests using a comparator rather than op amp, at least for the output, a 'relaxation oscillator' is probably the best way to go, wich is just an inverting schmit trigger with negative feedback.
the control voltage can adjust the current in the negative feedback via a voltage dependant resistor such as a fet or current source + current mirror + steering diodes.
its possible to do it with a ne555 timer.
Colin =^.^=
If you want a linear control curve, beware the delay through the comparator, 555, or whatever you use.
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
Theres a technique to use an inductor in series with the feedback capacitor to make the cycle end earlier at higher frequency and so compensate for the comparator delay.
Colin =^.^=
capacitor
the
actualy make that a resistor not an inductor lol.
Colin =^.^=
Nope, not an inductor, a resistor, such that tau = R*C = tdelay, and you charge and discharge the capacitor with currents... it's NOT the "feedback capacitor".
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
capacitor
the
I think i just beat you to it with the correction at least on my news server lol, with a 555 type its not what you would think of as negative feedback but with a relaxation type using an inverting schmitt trigger the capacitor is in the lower half of the neg feedback RC divider, and the extra resistor would be in series with the capacitor but still in the lower leg. of course the upper leg would be variable resistance or preferably variable current.
using the op amp integrator type, the resistor would be in the output of the op amp, the triangle is still taken from the capacitor if thats what you want, but the comparator is fed from the op amp output directly.
A picture is worth a thousand words, however I got this nugget of info from a post in here quite some time back wich went into more detail with a nice schematic.
Colin =^.^=
It was probably my post. I discovered that trick at least 30 years ago ;-)
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
Here's a post from 2004 where I mention that the technique was discussed in a previous post of mine (which I still can't locate)...
Path: archiver1.google.com!news2.google.com!news.maxwell.syr.edu!border1.nntp.ash.giganews.com!border2.nntp.ash.giganews.com!nntp.giganews.com!cyclone1.gnilink.net!gnilink.net!peer01.cox.net!cox.net!p01!fed1read07.POSTED!not-for-mail From: Jim Thompson Newsgroups: sci.electronics.design Subject: Re: Triangle to sinus for high frequencies - how? Message-ID: References:
X-Newsreader: Forte Agent 1.93/32.576 English (American) MIME-Versi [snip]
[snip]I discussed this technique here several years ago. It not only fixes the delay overshoot problem but also linearizes the control curve when used for a VCO.
...Jim Thompson
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
Wasn't that designed by some old curmudgeon?
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it.
[snip add-resistor-to-555-timing-cap trick]
Cheers, James Arthur
Yep. That's the thread! Thanks!
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
Yep. A REALLY OLD curmudgeon. MRI next week to look at why I've developed leg pain in my left leg only... sufficient pain to make me limp :-(
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
Ah yes I remember it well, but sheesh was it realy 2002 ? shame the drawings get screwed when viewed via google, I wonder if theres an unscrew it up button somewhere.
Colin =^.^=
ah found it right at the top, I wonder what happened to Win's fig tree he had to bury ?
Colin =^.^=
My pleasure.
James
I'll pray for you, my freind. I have swelling and pain in both legs too, but you're the one who claims to be older than dirt. ;-)
PS, don't tell them how many parts of the MRI machine you designed. They don't like it when the patient knows how their toys work. :(
Yep, I enjoy tweaking them. Particularly the ultrasound stuff... NO BRAND out there I didn't have a hand in the analog front-ends ;-)
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.