A Circuit to Convert Random Pulses into Uniform Pulses

Author: J.B. Hoag

The left half of the circuit of Fig. 30 I will convert random pulses of from 30 to 3,000 counts per minute into pulses of uniform length and amplitude.

Fig. 30 I. A circuit to convert random pulses into uniform pulses. Also, a frequency meter. (See Rev. Sci. Inst., Dec. 1936)

It is basically a multivibrator, but possesses one marked difference from the usual form of this circuit; namely, that the grid of tube 1 (part of a 6N7 tube) is biased negatively beyond cutoff, whereas the grid of tube 2 is at the more usual zero bias voltage. This is accomplished by passing current from the B supply through R₁ via the 50,000-ohm resistor. Thus, at the start, 1 is off and 2 is on. A positive pulse on the grid of 1 trips this tube, current flows through R₂, reducing the voltage on the plate of 1. This sends a negative pulse through C₂ onto the grid of the tube 2. The plate current through 2 is thereby reduced and its plate voltage increased. This positive pulse passes through C₃ to the grid of 1, augmenting the original input pulse. The interaction continues until the plate voltage on 1 is very small. The circuit remains in this condition until the charge on C₂ leaks to the cathode through R₄. When the grid of 2 reaches a certain critieal voltage, the entire process reverses itself to restore the original conditions (1 off and 2 on).

Thus an input pulse of any size or duration (within limits) initiates a series of events wherein 2 is turned off and then back on again sharply after a definite time interval determined by the circuit constants and not by the input pulse. The resultant potential variations across R₃, and across the output terminals shown in Fig. 30 I, are of square wave-form.