Page 223 - Op Amps Design, Applications, and Troubleshooting

Triangle-Wove Oscillator 205

In the case of the circuit in Figure 4.11, the threshold voltages are computed as

We are now ready to compute the frequency of operation. Since both positive
and negative saturation voltages, as well as both thresholds of A& are equal in this
circuit, the time for either alternation can be computed with Equation (4.36).

In our present case, these times are computed as follows:

13 V + 6 V
±
t = 470 kQ. x 0.1 uF x In = 46.93 ms
^ 13 V - 6 V
The total period for one cycle is, of course, twice the time computed with Equation
(4.36). The frequency is simply the inverse of the total period, which is

In our particular circuit, the frequency of oscillation is found as follows:

4*5.3 Practical Design Techniques
Now let us design a dual ramp oscillator similar to the one shown in Figure 4.11.
For this design, we will strive for the following design goals:

1. Frequency of oscillation l.Skilohertz
2. Ramp amplitude ±3 volts

Calculate the Values for R 2 and &a* Resistors R 2 and R 3 establish the thresh-
old voltages for comparator A 2. These voltages in turn determine the output
amplitude of the ramp voltage. The ratio of R 2 to R 3 can be found by applying
Equation (4.35).