reg: square wave to sine wave converter

[deepika97]

Hi,

I am working on a feedback circuit. I am using a sinusoidal signal to excite a sensor. I need to control the output voltage in the range of 100-200mV. So I am working with an AGC cirucit which is a real complicated one. So I have thought of using a simple diode clamping circuit for this but as it generates a square wave. I need a sine wave to be fed back to the sensor for the excitation again since the square wave gives spurious frequencies. I am operating my circuit around 1K-500KHz. If it would be great if anyone can suggest a simple circuitry with couple of opamps, resistors and capacitors.

Regards,
Deepika

 

[Siniša]

AGC cicuits should not be too complicated, and it very likely best choice for you. Triangle to sine shaping with resistor/diode networks is done in a lot off signal generators, just search for manuals with schematics on the net for example. I think this might be more comlicated than building AGC.

 

[zeeshanzia84]

use a low pass filter

the sharper edges of the square wave are due to the higher frequency components...so as you remove them, you get a smoother and smoother waveform.

 

[FvM]

I don't exactly understand what's your starting point. If you have a sine signal originally, I would use an analog multiplier or a JFET/MOSFET as controllable resistor. If it's a square wave, filters as suggested should help.

 

[LvW]

As mentioned in both contributions above, filtering the squarewave with a lowpass (or bandpass) is the most direct way to produce "something like a sinewave". The required filter order depends on the desired quality of the sine wave (THD).
However, this method works only for a fixed frequency.

Another - a bit unknown - method uses the classical differential amp (longtailed pair) to convert triangle waves to sine waves. This is in a broad frequency band independent on frequency, however, this method works only for a fixed amplitude.

Example: for an amplitude of 80 mV you get a sine wave with a THD of app. 1.5%.

Disadvantage: The squarewave has to be converted to triangle before (Integration)

 

[lladnar23]

Yea - for the most part, there are two main approaches: lowpass or bandpass filtering to remove harmonics, and "shaping" a triangle wave with diodes, etc..