Frequency detector suitable for circuit integration - has low-pass RC filters, driving comparators and gate

摘要

The arrangement for detecting frequencies has a pulse shaper (3) via which the input signal is fed in as a square wave. It is simplified compared to conventional arrangements contg. expensive components such as up-down counters and can be produced in integrated form. The pulse shaper output drives an inverter (4) and both drive two RC low pass filter circuits (8a,9a,11a,12a; 8b,9b,11b,12b) via two controlled changeover switches (5a,5b) driven by clock pulses phase shifted w.r.t. each other. Each filter output drives two comparators (16a,16b,17a,17b) whose outputs are connected to an OR gate (18) with as many inputs as there are comparators. The comparators produce binary signals indicating when upper and lower voltage levels are exceeded. The levels corresp. to sinusoidal components in the filter inputs which can just pass through undamped.