Generating Triangle Waves

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Direct links to other pages:
Basic Summing:	[Setting the Gain Coefficient] [Analog Addition] [Adding a Fixed Constant]
Variations in Feedback Circuits:	[Integrators] [Differentiators] [Logarithmic Amplifiers] [Non-Inverting Amplifiers] [A Difference Amplifier] [Increasing the Output Current Capacity] [A Half-Wave Rectifier] [A Full-Wave Rectifier]
Mixing Analog and Digital Technologies:	[Comparators] [Digital to Analog Conversion] [Analog to Digital Conversion]
Generating Waveforms:	[A Square Wave Generator] [A Triangle Wave Generator] [A Sine Wave Generator]
Operational Amplifiers:	[Characteristics of Operational Amplifiers] [Inside the 741]

Generating Triangle Waves

In the basic square wave generator circuit, a gradually-charging capacitor was used to help set the timing or frequency of the circuit. However, since it was only charging through a resistor, it necessarily charged on a logarithmic curve, rather than as a linear ramp. Can we use an op amp integrator here to obtain a linear triangle wave along with the square wave?

A generator for both square and triangle waves

In the circuit to the right, we use a separate integrator to generate a ramp voltage from the generated square wave. As a result, we can get both waveforms from a single circuit. The phase relationship shown between the two output waveforms is correct — remember that the integrator inverts as well as integrating, so it will produce a negative-going ramp for a positive input voltage, and vice-versa.

Because we are now using an op amp integrator to get the triangle wave, we no longer have a logarithmic response anywhere in the circuit. Therefore, the equation for the operating frequency is simplified to:

f_out =	1	(	R₂	)

	4R_tC		R₁

The squarewave amplitude is still the limit of voltage transistion, which we are assuming here to be ±10 volts. The triangle wave's amplitude is set by the ratio of R₁/R₂.