This is a simple sawtooth generator circuit. The advantages of this circuit are low cost and produces an auxiliary square wave at the same frequency. This circuit can be used to sweep the frequency of another generator. Here is the circuit :
A voltage-controlled current source is formed by IC1 with R1 and Q1. The C1 is discharged by current Io until it’s voltage is less than 1.66V. It will swing its output to 5V and trips the IC2A comparator. The C1 is charged by current through the diode-connected transistor (Q2) until its voltage reaches 3.33V, so the IC2A output to swing back to ground. The output frequency is determined by :
fOUT = (3(5V +VC)/5V)(1/R1C1).
We can set the fOUT as high as desired by adjusting the values of C1and R1, subject to the limitations of comparator IC2A’s slew settling and rate time. The frequency range over which it can operate determined by generator’s linearity. [Source: maxim-ic.com]