Ring discriminator

A ring discriminator comprising means for receiving an input ringing signal, a counter, means for applying clock pulses to the counter, means for enabling the counter to count clock pulses from a cycle of ringing current, and means for determining a clock pulse count on the counter to distinguish a frequency characteristic of the ringing signal, the cycle of ringing current being a first cycle in a ring burst, the counter enabling means being comprised of a differentiator for differentiating leading edges of the input ringing signal, an integrator for generating a ring burst envelope pulse for the duration of each ring burst of the input ringing signal, a NAND gate for receiving the differentiated leading edges and the ring burst envelope pulse, means for generating an enable pulse beginning at every second differentiated leading edge and ending at every alternate following differentiated leading edge, means for inhibiting the enable pulse generating means from the end of a first enable pulse and means for applying a resulting single enable pulse to the counter.