The TTL 74123 integrated circuit consists of a monostable that can be configured to generate voltage controlled signals as shown in the figure. The maximum frequency of this circuit can reach a few dozen megahertz and even more if the faster 74123 subfamilies are used. In this circuit the control voltage varies between 0 and 6 V (may actually be a little more than 5 V of the power supply) when frequencies are obtained according to the graph in the figure below.
In this case, the frequency will typically vary between 10 and 60 kHz, with rectangular signals at the output. The amplitude of the signals is equal to the voltage used for the power supply, in this case 5 V. The diodes used in this circuit are commonly used as 1N4148 or equivalent.
