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Waveform generator circuits

2017-11-24 19:44  
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There are many different types of waveform generator circuits for many different uses. Here are some which I've collected. I leave it up to you to find uses for them!

Dual Ramp Generator

 

Circuit /files/Images/Article/Circuit_Diagram/ramps.gif

The first circuit is a dual ramp generator where the positive and negative ramps are generated separately. This circuit was used as a ramp generator for a transistor curve tracer: the positive going ramp was used for testing NPN transistors and the negative ramp for testing PNP transistors. The two ramp outputs are at A and B. The A output sits at -12v whilst the B output is ramping and then it ramps positive while the B output sits at 12v. The two waveforms are shown below the circuit and ramp lengths are determined by the integrator (-ve feedback) capacitors and the 'set' presets. For transistor testing this is nice since each ramp is 50% of the duty cycle so the transistor gets a chance to rest between ramps. If the output is selected with respect to ve or negative (which requires an isolated supply) the polarity can be switched as shown in the bottom right of the diagram.

Three phase oscillator

 

Circuit: /files/Images/Article/Circuit_Diagram/tpo.gif

The second circuit is a 3 phase squarewave oscillator, or tristable. Its operation should be reasonably obvious and it is like a simple bistable oscillator with 3 stages.

Quadrature (sine/cosine) voltage controlled oscillator

 

Circuit /files/Images/Article/Circuit_Diagram/quad.gif

This is a voltage controlled oscillator with a difference: it gives a quadrature output which is shaped as shown in the diagram, with an output which approximates to a sine/cosine waveform.

If you have difficulty understanding it this is because it does not use standard op-amps but an LM3900 which is a Norton op-amp - it works on differential currents, not on differential voltages. The LM3900 is a very versatile op-amp which has some very special advantages over standard op-amps but is not nearly as commonly used: I suspect that few students are taught about it so few consider using it.


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