voltage to frequency converter circuit (VCO)

[[email protected]]

i'm working on a design project right now to create a voltage
controlled oscillator using only opamps and discrete components. I'm
able to create a square and triangle waveform easily and i've found
many methods to create a sine waveform such as piecewise breakpoint and
jfet amplifer from the triangle wave.

However, I'm having trouble finding information about a voltage to
frequency interface so that i can vary the frequency of the waveforms
using a DC voltage. There needs to be two ranges of voltages from
0.1-0.5V which control the frequency with 200hz/V and 1khz/V (user
selectable from one of the two).

Any help is appreciated. thanks.

 

[Tom Bruhns]

i'm working on a design project right now to create a voltage
controlled oscillator using only opamps and discrete components. I'm
able to create a square and triangle waveform easily and i've found
many methods to create a sine waveform such as piecewise breakpoint and
jfet amplifer from the triangle wave.

However, I'm having trouble finding information about a voltage to
frequency interface so that i can vary the frequency of the waveforms
using a DC voltage. There needs to be two ranges of voltages from
0.1-0.5V which control the frequency with 200hz/V and 1khz/V (user
selectable from one of the two).

Any help is appreciated. thanks.

I'm a bit confused whether you need the VCO to have native sinewave
output or not. Assuming that a fixed-amplitude sawtooth (triangle)
output is ok, the common way to do it is to use an op-amp integrator
which integrates between two setpoint voltages, say +1V and -1V. A
resistor feeds current into the integrator, just a capacitor from op
amp out to the (-) input. The voltage which feeds that resistor
determines the ramp rate of the integrator, and thus the frequency.
The control voltage input can be fed to an inverter to generate a
negative version of itself, and then the integrator input resistor is
switched between the control voltage and its negative to ramp down or
up, respectively. Which way it goes is controlled by some bi-stable
circuit that switches state when the integrator output limit in either
direction is reached. You can easily change either the capacitance or
the resistance in the integrator to change between 200Hz/V and 1kHz/V.

If you want native sinewave output, you _could_ build a pair of higher
frequency oscillators, controlled by varactor diodes, and mix
(multiply) the two outputs to generate the sum and difference
frequencies, using a simple low-pass filter to get rid of the sum
frequency. Making such an oscillator with a very linear f vs V
response is not easy.

I'm curious; is this a homework assignment?

Cheers,
Tom

 

[Jamie]

i'm working on a design project right now to create a voltage
controlled oscillator using only opamps and discrete components. I'm
able to create a square and triangle waveform easily and i've found
many methods to create a sine waveform such as piecewise breakpoint and
jfet amplifer from the triangle wave.

However, I'm having trouble finding information about a voltage to
frequency interface so that i can vary the frequency of the waveforms
using a DC voltage. There needs to be two ranges of voltages from
0.1-0.5V which control the frequency with 200hz/V and 1khz/V (user
selectable from one of the two).

Any help is appreciated. thanks.

http://www.musicfromouterspace.com/analogsynth/VCO200503REV01/VCO200503REV01.html

that mite give you something to work with.

 

[john jardine]

i'm working on a design project right now to create a voltage
controlled oscillator using only opamps and discrete components. I'm
able to create a square and triangle waveform easily and i've found
many methods to create a sine waveform such as piecewise breakpoint and
jfet amplifer from the triangle wave.

However, I'm having trouble finding information about a voltage to
frequency interface so that i can vary the frequency of the waveforms
using a DC voltage. There needs to be two ranges of voltages from
0.1-0.5V which control the frequency with 200hz/V and 1khz/V (user
selectable from one of the two).

Any help is appreciated. thanks.

I've been f****** programming all week and felt an extreme urge coming on
to design something for real. (better now
With smaller Cap, circuit is good to about 40kHz.

(max 3.5V) +5V
0 to 500mV i/p .-----o-. 10n|| Triangle
o-o--------------------o1 14 | .-||---.6V pkpk Square
| ___ 10k | | | || | ___
| .-|___|-. | 2o--. | | .-|___|-.
| | | | | | ___ |6|\| | | 15k |
| | +5V | | IC1 | o-|___|-o-|-\ | ___ | |\ |
| ___ |2|\| | | | | Rset | >-o|___|-o-|+\ |
'-|___|-o-|-\ 1 | | 9o--' .-|+/ 7 10k 10| >--o-o
10k | >--o----o8 | |5|/| .--|-/ 8 |
.---|+/ | | | | 9|/ |
| 3|/| | | -o- -o- |
-o- -5V .-o3 5o-. 0V 0V |
0V | | | | |
.---o-o6 13o-o------------------------------'
| | |
.-. | | Rset=7350 ohms for 1KHz/V
10k| | | 4 7 | Rset=36750 ohms for 200Hz/V
| | '-o---o-' IC1 74HC4066
'-' -5V -5V Opamp TL084 (+5V p4,-5V p11)
|
+5 -o- "Voltage controlled Oscillator".

(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

 

[Jan Panteltje]

I've been f****** programming all week and felt an extreme urge coming on
to design something for real. (better now
With smaller Cap, circuit is good to about 40kHz.

(max 3.5V) +5V
0 to 500mV i/p .-----o-. 10n|| Triangle
o-o--------------------o1 14 | .-||---.6V pkpk Square
| ___ 10k | | | || | ___
| .-|___|-. | 2o--. | | .-|___|-.
| | | | | | ___ |6|\| | | 15k |
| | +5V | | IC1 | o-|___|-o-|-\ | ___ | |\ |
| ___ |2|\| | | | | Rset | >-o|___|-o-|+\ |
'-|___|-o-|-\ 1 | | 9o--' .-|+/ 7 10k 10| >--o-o
10k | >--o----o8 | |5|/| .--|-/ 8 |
.---|+/ | | | | 9|/ |
| 3|/| | | -o- -o- |
-o- -5V .-o3 5o-. 0V 0V |
0V | | | | |
.---o-o6 13o-o------------------------------'
| | |
.-. | | Rset=7350 ohms for 1KHz/V
10k| | | 4 7 | Rset=36750 ohms for 200Hz/V
| | '-o---o-' IC1 74HC4066
'-' -5V -5V Opamp TL084 (+5V p4,-5V p11)
|
+5 -o- "Voltage controlled Oscillator".

(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

Yes, nice, but if you want only a square wave, and use chips anyways,
why not use the 74HCT4046 PLL.
It has has a VCO.

But I think I can do this simpler with discrete components:

----------------------------------------- +12V
| | |
[ ] [ ] R1 [ ]
| | |
| |</ e |
|---| PNP T2 | T3
| |\ c |--
T1 | --------\ | unijucntion transistor
| | |--
|---- d | |------------ pulse out
----| JFET | |
|---- s | [ ]
| === |
Uin [ ] | C1 |
| | |
------------------------------------------- 0V



Capacitor C1 will be charged by constant current source T2.
The amount of current determines how fast T3 will trigger.

Current source T2 is controlled by T1
You probably want top add a si diode for temp compensation of T2.

[] are resistors (European symbol).
Does anybody still remember UJTs? Great stuff.
If you want a square wave add a 2 transistor flip flop
OK, have to dash now.

 

[martin griffith]

On a sunny day (Fri, 20 Oct 2006 20:29:45 +0100) it happened "john jardine"
<[email protected]> wrote in

But I think I can do this simpler with discrete components:

----------------------------------------- +12V
| | |
[ ] [ ] R1 [ ]
| | |
| |</ e |
|---| PNP T2 | T3
| |\ c |--
T1 | --------\ | unijucntion transistor
| | |--
|---- d | |------------ pulse out
----| JFET | |
|---- s | [ ]
| === |
Uin [ ] | C1 |
| | |
------------------------------------------- 0V

Does anybody still remember UJTs? Great stuff.

2N2646, still got a copy of the GE transistor manual somewhere with a
whole UJT chapter, (and one on tunnel diodes)


martin