reciprocal counter

see also:

A reciprocal counter measures a frequency by measuring the time between a certain number of edges of a clock signal. This is opposed to the approach of a simple counter that counts the number of signal edges in a certain time interval. All of our TDCs can be used as reciprocal counters with very high precision. To measure frequencies that are higher than the maximum count rate of a given TDC an external prescaler is required.