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Sine wave generator using diode network

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abbeyromy

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Hi guys,

I was earlier posting my queries in someone else post, so thought of starting this new thread. I hope this is not an issue with moderators.
Ok so I was working on generation of sine waves from triangular wave. One circuit I able to successfully test on pspice using differential pair and op-amp. thanks to FvM and other seniors for the help!

Now I saw a circuit on web showing diodes being used for this purpose. See the attached pdf. I tried to make my circuit in that line but was unsuccessful as I am still getting triangular wave at output. Any suggestions seniors? Can somebody explain the circuit in detail?
Really need your help guys!
-Hemanshu
 

Generator parameters in your simulation are wrong. Why not simulate complete function generator and analyze voltage levels of triangle signal before diode shaper cstage if you are unable to calculate it from complete circuit.
 

@Borber

Actually I was avoiding drawing the complete circuit because I dont know how to model R5 in the function generator circuit.

If you have any idea about using Diode for sine wave generation. Please suggest.I was just looking for a simple circuit to implement this.
 

OK, R5 replace with fixed resistor (100k or 500k).
Another thing you can do is to change your simulation circuit. Non-inverting input of OPA connect to ground so as diode branches on right side or set R25 to 0ohm. Then change V16 generator amplitudes as needed.
 

    A

    abbeyromy

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To understand the sine generation all you need to look at is the diode section - you can ignore the opamp. It works by simply rounding off the peaks of the triangle. Just connect the triangle waveform generator to the diodes (with the resistors) and increase the amplitude until it starts to round off.

Keith

Edit: I seem to think there is an interesting example in Hans Camenzind's online book. Just Google his name. Unless it has changed you can download his book for free from his web site.
 

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    abbeyromy

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Just connect the triangle waveform generator to the diodes (with the resistors) and increase the amplitude until it starts to round off.
Click to expand...
Yes, two or four diodes, a triangular voltage and a series resistor are all you need. The offset voltage to the diode network
is e.g. only used because the original circuit has a single supply voltage.

Among the different sine shaper circuits, the simple diode circuits gives least sine quality, the said online book

shows a multi transistor circuits as utilized in ICL8038.
 

    A

    abbeyromy

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Thanks for posting a proper link. I cannot cut & paste web addresses on my mobile phone.

Keith
 

@keith1200rs/FvM

Hey I tired simulating an input triangular wave + 2 diodes + series resistor circuit but still I am getting triangular at the output. Also the book you said I am not able to find where this is mentioned in the book...
Really sorry.. I dont like spoon-feeding but I am not able to get this circuit working :(

Thanks for the help..if possible can you draw a sample circuit?
 

Increase generator voltage untill top of output signal is quasi rounded. Start with 2Vpp.
 

    A

    abbeyromy

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Awesome Man this circuit works fine..Thanks a ton!!

As keith pointed out earlier that the circuit works by simply rounding off the peaks of the triangle. I just wanted to know as to why this happens in a layman's term?

Also if I am using the circuit as shown by you I expect around 1-1.2V output ( adding forward drop across diodes). If I use only one diode in each section I get around 0.5V-0.6V. So basically the peak voltage we expect depends upon the number of diodes in the circuit?

The more in input voltage above 1V the more the flattening of sine waves right? Maybe because the max output I can get is the forward drop and more input means more time we are stuck with the same forward drop at output peak.

Please correct/suggest!!
Thanks again for taking your time out for helping me...
 

@keith1200rs

Thanks for the page.. This one looks so complicated though! Hey if possible can you answer the above post having a few questions..
 

abbeyromy said:
@keith1200rs

Thanks for the page.. This one looks so complicated though! Hey if possible can you answer the above post having a few questions..
Click to expand...

The circuits rely on the soft 'knee' in the voltage-current curve of the diode. You cannot change where that happens so yes, it has to work at a particular voltage. You can alter the 'softness' a little by changing the series resistor. I seem to remember with my video circuit I had to boost the voltage first - perform the shaping then attenuate because the video signal was only 0.7V.

Keith

Added after 2 minutes:

It always seems a bit of a 'Heath Robinson' approach to creating a sine wave, but it does work provided you use a fixed amplitude sine wave.

Quite a few years ago I made an LCD lineariser for a medical application which made three slopes with a combination of diodes & resistors working on the RGB video signals.

Keith

(my posts seem to be getting out of order).

The Hans Camenzind circuit was for a custom IC.

Keith
 

This circuit is implemented in ICL8038 Precision Waveform Generator/Voltage Controlled Oscillator IC. Adjusted THD is only 1.5%.
 

Hans claims 1% is his book so that sounds about right. Did he design the 8038? I know he did the 555.

Keith
 

This old appnote from National may be of some help **broken link removed**
 

The circuits rely on the soft 'knee' in the voltage-current curve of the diode. You cannot change where that happens so yes, it has to work at a particular voltage. You can alter the 'softness' a little by changing the series resistor.
Click to expand...
Assuming an ideal diode characteristic (almost realistic in this case), you'll get an optimal triangular input voltage. For single 1N4148
pair with 10k series resistance, it's 1.25 Vpp (or 2.5 Vpp for the double pair) , resulting in about 1.2% THD. Changing the series resistor
shifts the operating point along the exponential diode characteristic, resulting in a slightly different optimal voltage, but basically the same
waveform.

To change the output voltage, you obviously need an amplifier stage.
 

abbeyromy said:
.....................
Ok so I was working on generation of sine waves from triangular wave. One circuit I able to successfully test on pspice using differential pair and op-amp. thanks to FvM and other seniors for the help!
...................
-Hemanshu
Click to expand...

Since I don't know how "successfull" you was, just a short remark to the method mentioned by FvM within this thread:

You can achieve a THD of app. 1.3% at the BJT differential pair output, if the triangle input amplitude is selected to be app. 80 mV. For my opinion, it is the simplest method (if you can live with the THD).
 

Yes, I know. It was only my intention to inform you about my experience concerning signal amplitude.
LvW
 

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