SINGLE FREQUENCY DETECTION CIRCUIT

PURPOSE:To detect arbitrary single frequency by comparing the output of a 1/2 frequency dividing circuit with the output of a count detection frequency/ band width setting switch by a count number comparing circuit to send out the comparing result. CONSTITUTION:An analogue signal is inputted to a comparing circuit 1 and compared with a preset min. detection level to send out output having the pulse width corresponding to the cycle coinciding with the cycle of the analogue signal and the level of the analogue signal. A TT level converting circuit 2 receives the input of said pulse to send out pulse output converted to a TT level and inputs the same to a 1/2 frequency dividing circuit 3 to repeat reversal at rising and falling and the pulse output is divided to 1/2 in frequency to be converted to a signal having a pulse width optimum in the detection of frequency and said signal is sent to a count number comparing circuit 5. Further, a detection frequency/band width setting switch 4 is controlled to send output wherein desired detection frequency and a band width are set to the circuit 5. The circuit 5 compares both input signals and regards that the frequency in a detection band is being received when a comparing result is sent out and can detect the frequency of the input signal.