In electronics, waveforms are primarily plotted in terms of voltage and time. The frequency and amplitude of the signal can vary depending on the circuit. There are many kinds of waveforms, such as sine wave, square wave, triangle wave, ramp wave, sawtooth wave and so on. We have designed sine wave and square wave generator circuits. Now, in this tutorial, we will show you how to design a sawtooth generator circuit with adjustable gain and waveform DC offset using an operational amplifier and 555 timer IC.
A sawtooth wave is a non-sinusoidal wave that looks similar to a triangle wave. This waveform is named a sawtooth because it looks like a sawtooth. A sawtooth wave differs from a triangle wave in that a triangle wave has the same rise and fall time, whereas a sawtooth wave rises from zero to a maximum peak value and then quickly falls to zero.
Sawtooth waves are used in filters, amplifier circuits, signal receivers, etc. It is also used for tone generation, modulation, sampling, etc. An ideal sawtooth wave looks like this:
Operation of sawtooth generator circuit
To generate the sawtooth waveform, we have used 555 timer IC and LM358 dual op-amp IC. In this circuit we use transistor T1 as a controlled current source with adjustable emitter and collector currents. Here 555 timer IC is used in astable mode.
Resistors R2 and R3 set the bias voltage used to bias the base pin of PNP transistor T1. And, R1 is used to set the emitter current, effectively setting the collector current, and this constant current charges capacitor C1 in a linear fashion. That’s why we receive the ramp output. By replacing R1 with a potentiometer you can adjust the ramp speed.
This allows the capacitor to charge and discharge by shorting the trigger, discharge and threshold pins of the 555 timer directly to capacitor C1.
Here, the first operational amplifier, O1, acts as a level-shifting inverting buffer. Since it is an inverting buffer, the lower part of the ramp will become the upper part of the inverting ramp.
The output of this operational amplifier is then connected to POT P1 to adjust the amplitude of the signal. Similarly, Op-amp O2 is used to adjust the DC offset of the signal. And, the output is taken from the output of the operational amplifier O2.
The oscilloscope’s first probe is connected to this output, and the second probe is connected to the trigger pulse, which comes from the output of the 555 timer IC. Therefore, after connecting the two probes of the oscilloscope, the output of the sawtooth wave will be as shown in the following figure:
Move potentiometers P1 and P2 respectively to adjust the gain and DC offset of the signal.