# Operational Amplifiers circuits

Posted on Feb 4, 2014

The Wien-Bridge oscillator fulfills these requirements because there is a low pass filter, a high pass filter and a 180 deg. phase shift from the feedback networks from the input to output. This totals 360 deg. to start the circuit oscillating. If all three of the criteria are met and you have a resonant Grequency under 1 MHz, then you have a cir

cuit that produces a Sine Wave from a DC power source. The second stage of our Function Generator is this Schmitt Trigger. This circuit is used to convert a Sine Wave into a Square Wave. This happens because the input signal is large enough to pass through both the lower and the upper voltage trip points. This is possible when the upper part of the Sine Wave hits the output voltage. The voltage will go directly to +Vsat and stay there until the lower peak causes it to go to -Vsat add infinitum. This circuit produces a "ramp" voltage. Normally you would have just a capacitor in the negative feedback loop. But because we want no output offset voltage, we had to put a resistor in parallel with the cap. Besides limiting the output offset, it produces our "Virtual Ground. " This virtual ground is created by the 741`s very high input impedance. About 150 M*`s of it. What happens is the input resistor is connected to the positive input and a resistor coming from the output signal is connected also to the +in. Total current will go through the first resistor and split towards the second resistor because it`s an easier path to ground. When this is set up like this, as long as both resistors are less than 150 Megs, a ratio situation occurs between them. Depending on the ratio, or Gain created, you can control how much amplification it has. Now throe in the cap and a Saw Tooth wave shape is created. In conclusion, the 741 Op Amp can...

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