Subject: Liner Integrated Circuits

Topic: Non-Linear Applications of Operational Amplifier

Difficulty: Low

Triangular Wave Generator Using Op amp

A Triangular Wave Generator Using Op amp can be formed by simply connecting an integrator to the square wave generator.

Triangular wave is generated by alternatively charging and discharging a capacitor with a constant current. This is achieved by connecting integrator circuit at the output of square wave generator as shown in the figure above.

Assume that V’ is high at +Vsat. This forces a constant current (+Vsat/R3) through C (left to right) to drive Vo negative linearly. When V’ is low at —Vsat, it forces a constant current (— Vsat /R3) through C (right to left) to drive Vo positive, linearly. The frequency of the triangular wave is same as that of square wave. This is illustrated in Figure below.

Although the amplitude of the square wave is constant (± Vsat), the amplitude of the triangular wave decreases with an increase in its frequency, and vice versa. This is because the reactance of capacitor decreases at high frequencies and increases at low frequencies. In practical circuits, resistance R4 is connected across C to avoid the saturation problem at low frequencies as in the case of practical integrator as shown in the Figure below

To obtain stable triangular wave at the output, it is necessary to have 5R3 C2 > T/2, where T is the period of the square wave input.

The time period of the output of the square wave generator is T = 2 x 2.303 Rf C x log((2R2+R1)/R1) which is the same for triangular wave generator. Frequency of the output f = 1/T