Function Generator 1

Posted on Feb 4, 2014

At some time, you`ve probably run into this magical instrument in the lab - the function generator. Just turn the waveform selector knob and a triangle, square or sine wave appears at the output! Turn another knob and the frequency of the signal changes. Now you can feed the square wave into an amplifier you`re testing to see how quickly it respon

ds. Is there any over shoot or ringing Or maybe you`re testing an audio amplifier and you feed it a 1 kHz sine wave. Is there any distortion at the output I looked at my handy function generator and wondered what kind of circuit creates these waveforms A search on the web produced a few schematics. Although they all took different circuit approaches, the essence of each one resembled the overall topology shown above. At the core of the function generator is a triangle wave generator. How do you generate a triangle wave The most common way is to get a capacitor and then alternate charging it and discharging it. But how to you get a nice linear ramp across the capacitor The key here is to charge and discharge it with a constant current source. Mathematically, here`s how it works. A capacitor integrates a current, i. Looking at function generator schematics you`ll find different ways to implement constant current sources and integrators. One circuit uses the classic op amp integrator. To create the negative ramp, the circuit looks like this. In the SPICE circuit, vs and R1=10k set up I1. An inverter XOP2 creates -vs from vs. I2 is created using voltage -vs and with R2=5k. R2 is switched into the circuit by voltage-controlled switch S1. The integrator is created by XOP1 and CI. The next challenge is switching between the positive and negative ramps. Typically, two voltage thresholds (high and low) are created to set the...

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