Voltage controlled oscillator with a sine wave output.

Thread Starter

alexmd

Joined Dec 5, 2019
13
Hey guys,
I have a really big problem, I have a project at university and I am stuck on one part. I need to make a VOC with a sine wave output (10kHz - 15kHz), I have 4 different values for the input (3V, 4.5V, 6V, 7.5V), but I am not sure how can I make a stable oscillator.
 

kubeek

Joined Sep 20, 2005
5,724
Does it need to be made from discrete parts, or can it be any convenient solution? Depends on what are your requirements. If I needed such circuit as building block for something else, and not an excercise in analog design, I would probably use a microcontroller to do it.
 

schmitt trigger

Joined Jul 12, 2010
275
There used to be an old app note from RCA semiconductor, which showed how to make a voltage tuneable sinewave oscillator with a transconductance opamp. The CA3080.

Unfortunately RCA semi has been kaput for decades, and the different companies which have successively acquired the assets, haven't kept the old app notes online.
Additionally, the CA3080 has been obsolete for at least 15 years, although you still find some on e-bay.
 

SLK001

Joined Nov 29, 2011
1,548
Hey guys,
I have a really big problem, I have a project at university and I am stuck on one part. I need to make a VOC with a sine wave output (10kHz - 15kHz), I have 4 different values for the input (3V, 4.5V, 6V, 7.5V), but I am not sure how can I make a stable oscillator.
Why were you assigned the task of making a VCO, when you don't know how to make a stable oscillator? And, making a VCO with a 50% control range is a challenge, even for the experts, especially in the kHz range. Where are your specs for the end result? What do the 4 voltages you give mean?

So, "yes", you have a really big problem.
 

Thread Starter

alexmd

Joined Dec 5, 2019
13
I have to make a "gesture-controlled" glove which is actually one finger with a 9V source and the others with resistors so I can have a voltage divider. It is connected with an oscillator which needs to output a sine wave with different frequencies in the (10 to 15kHz) range.
 

LvW

Joined Jun 13, 2013
1,054
Well, there is an oscillator principle which is rather unknown - however, it could be a solution of your problem.
This oscillator is called "GIC resonator" and needs two operational amplifiers. It is based on the well-known GIC (introduced by Antoniou) which is a very versatile active block used in active filter design.
This oscillator topology has a special feature: It can be tuned with a single resistor that is grounded and which can be, therefore, replaced by a FET for voltage tuning. It is important to mention that such a tuning does not touch the oscillation condition.
 

AnalogKid

Joined Aug 1, 2013
8,484
National Semiconductor (now a part of TI) LM13700 datasheet, figure 17. This is an adaptation of a phase-shift oscillator, one of the easier sine circuits. The text description calls out figure 16 in error. The part is in stock at Digi-Key and Jameco.

ak
 
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LvW

Joined Jun 13, 2013
1,054
Yes - that is the circuit I have mentioned....if you have further questions......do not hesitate.
As an attachement I give you a revised version of the paper - with some test results
 

Attachments

LvW

Joined Jun 13, 2013
1,054
As you know, the FET must be operated for small VDS voltages (quasi-linear region). with the source node grounded. It may be very useful to use the FET in series with a suitrable resistor. This is a good solution because (1) the VDS voltage can be made rather small and (2) the linearity of this combination is better than the linear behaviour of the DS-path alone.

PS: FET used as a resistance is not the only method for realizing a voltage-controlled resistor.
For example, you also could use an OTA for this purpose.
 
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danadak

Joined Mar 10, 2018
4,057
For future ref this can be done quite easily with a single chip solution and maybe 10-15
lines of code.

PSOC 5LP is part familiy.

The DelSig A/D reads your V source and translates (with code) the V to DDS freq value
for DDS clock to the WaveDAC to produce the desired freq out of the WaveDAC. All
onchip, including vref for A/D.

Tool, compiler and IDE are free, dev board $ 10.

Right hand window show how few onchip resources were used. Lots of other stuff can
be incorporated into design. In fact 4 channels of this could be done onchip. Keep
also in mind WaveDAC can produce any arbitrary waveform, albeit limited in freq
to ~ 10's of Khz.


1575643071334.png



Regards, Dana.
 

AnalogKid

Joined Aug 1, 2013
8,484
the bad thing about the analog sine generators is that they are not quite sine - all of them . . . or the majority of
Disagree. The majority of analog sine generators - Wein, Phase Shift, Bubba, Bi-Quadratic, Gyrator, Twin-T, Butler, Clapp, Colpitts, Hartley, Pierce, etc. - do not depend on non-linear circuit components, such as the breakpoint diode waveshaping in your second link, to approximate a sinusoidal output shape. Some, like the Wein bridge oscillator, need a non-linear element to stabilize the output amplitude; but that is not the same thing.

ak
 

DickCappels

Joined Aug 21, 2008
6,452
How about a microcontroller with an on-chip A-to-D converter driving a Direct Digital Synthesis chip like the AD9833? Would that be cheating?
 

atferrari

Joined Jan 6, 2004
4,002
Why most people asking for help on their homework, do explain the task they were given instead of showing the actual text / graphics as received from the instructor?

Reminds me my secretary that when telling about last emails received, she used to comment them instead reading them verbatim to me. But then, one day I got my first mobile able to do email.
 
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