Schmitt Trigger Circuit

With a LO on U480B pin 7, the output at pin 3 goes LO as soon as the signal on U480B pin 6 reaches the switching threshold. The LO is applied to U480A pin 4 and, together with the fixed LO on pin 5, causes the output of U480B pin 6 via R480 to reinforce the switching action. As a result, the output signal at U480A pin 2 switches rapidly.

When the level from the filter network falls to the LO threshold level, the feedback supplied by R480 holds the Schmitt Trigger switched HI for a short time. The amount of time involved prevents noise occurring exactly at the threshold level from causing false triggering.

When either AUTO or NORM triggering is selected, input pin 6 of U480B is held LO, and the Comparator output signal on U480B pin 7 supplies the input to the Schmitt Trigger circuit.

The output of the Schmitt Trigger circuit is obtained from U480D pins 9 and 15. The differential output signal derived from U480D is applied to a two-transistor level-shifting circuit composed of Q492 and Q493. The level-shifting circuit converts the ECL logic levels to TTL logic levels required for the Sweep Generator. A signal obtained from the collector of Q493 is used to drive the Auto Baseline circuit.

0 0

Post a comment