Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Variable frequency sine wave oscillator

Status
Not open for further replies.

abhishek.2138

Full Member level 2
Joined
Dec 21, 2013
Messages
130
Helped
0
Reputation
0
Reaction score
1
Trophy points
1,298
Activity points
2,375
How to generate constant amplitude variable frequency sine wave USING OPAMPS???? Say the frequency to be varied by potentiometer...(20 to 50 Hz)

I am trying using low pass filters (square wave to sine wave) but the signal is attenuated as the frequency is increased..that is signal amplitude reduces...

Any help???
 

I designed a variable frequency sinewave oscillator that uses a switched-capacitor lowpass filter IC to produce perfect very low distortion stable signal amplitude sinewaves. The variable frequency clock for the squarewave generator is the same clock used to set the cutoff frequency on the switched-capacitor lowpass filter IC.

But you want to use opamps so make an active lowpass filter with a variable frequency using opamps and make its frequency adjusted with a pot ganged to the squarewave frequency setting pot.
 
Which switched-capacitor lowpass filter IC you have used for variable freq. sine wave oscillator??
 

I used two National Semi LMF40 ICs in series for a Butterworth 8th-order LPF a long time ago but it has been discontinued. Today Maxim have some.
I used a switched-capacitor LMF100 filter to make a variable frequency notch filter for a distortion analyser that measures down to very low amounts of distortion. it also uses the same clock as the generator so they track together.

My input to the LPF filter in my generator does not use a squarewave, instead it uses a (Don Lancaster Digital Sinewave) CD4018 counter and a few resistors to make a stepped sinewave that does not have any lower harmonics and the LPF removes the higher harmonics.
The distortion with a squarewave is 0.1% and with the stepped sinewave the distortion is below 0.001%.
Don Lancaster wrote the book called Cmos Cookbook.
 

How to generate constant amplitude variable frequency sine wave USING OPAMPS???? Say the frequency to be varied by potentiometer...(20 to 50 Hz)

I am trying using low pass filters (square wave to sine wave) but the signal is attenuated as the frequency is increased..that is signal amplitude reduces...

Any help???

Do you want to create the circuit by yourself (opamps, resistors, capacitors) or are you allowed to use special-purpose IC`s (like switchend-C blocks)?
 

20Hz to 50Hz is as very narrow range of frequencies so it will be simple to make a variable frequency active lowpass filter circuit track the frequency of the squarewave oscillator.
Did you look up Digital Sinewaves that are made with a clock, counter and a few resistors?
 

If you review the previous threads, you'll realize that 20 - 50 Hz can be tuned with a single resistor (resistor ratio 1:6.25) if you choose an analog sine oscillator.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top