If you need a triangle wave signal or a square one but you only have a sinewave generator, use this converter to avoid the trouble of beginning from scratch.
It is made up of two ICs: one LM13700 and one TL084.
The amplitude of the squarewave can be varied through P1 while potentiometer P2 varies the amplitude of the trianglewave signal. The converter can process signals from
6 Hz up to 60 kHz.
In many function generators, a triangle wave generator (which is usually made of a schmitt-trigger combined with an integrator) is the heart of the circuit.
The resulting sine wave is then synthesized from the triangle wave with the help of special diode networks.
The circuit featured here, however, does it the other way around. First, the sinewave is reshaped to a triangle. Finally, the triangle is reshaped to a square wave.
The sinewave is, however, not generated by this circuit. Therefore, you must get it from a sinewave source. The sinewave is reshaped by the opamp IC1A. The two resistors
R3 and R4 reduce the output level of the IC1A, since this output level swings back and forth from negative 15 volts to positive 15 volts.
The signal coming from IC1A is integrated by the combination of the transconductance amplifier IC1 and capacitor C2. The integration time factor can be easily adjusted with
a preset voltage level fed to pin 1 of IC1. The opamp IC2B is added to the circuit to act as an impedance converter. It prevents voltage shifts at the capacitor C2 that might
happen due to overloading.
The trianglewave can be sampled right from the output of IC2B. The following IC2C compares the trianglewave´s amplitude with the value which is preset through P2. The output of
IC2C controls the current regulator at the output of IC1A. This technique guarantees that the amplitude of the output signal remains independent from the input signal´s frequency.
The resistor R6 combined with the capacitor C1 play together so that the output level exactly matches the level that was preset by R4. They are connected in a feedback manner.
This technique solves the very common problem with high precision integrators - the sensitivity to offset voltages and stray currents. For example: a stray current (maximum: 7mA
at 75°C) can cause a slight change at the output signal.
We want the resulting square wave to remain clean. That is why it is important the triangle wave must remain clean. To achieve it, the time constant of the RC circuit is selected to be high.
This guarantees that the triangle wave can never influence the waveform to be integrated even at the lowest frequency levels.
This converter can process signals from 5 Hz with amplitude shifts of 0% up to 60 kHz with amplitude shifts of minus 10%. At higher frequencies - above 1 kHz - the circuit needs a
longer time to stabilize itself. This is due to the high time constant levels of the RC circuits.
You must set the maximal amplitude of the source signal to 1 volt. You can also use a battery to power the circuit since the current consumption is around 10 mA only.
Electronic Circuits volume 1.0 - Circuit Nr. 86
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
Click on the image to view the book.