Ramp technique

This technique is of great importance in analog to digital converters. Here a ‘ramp’ voltage is internally generated which rises linearly with time. When the ramp voltage becomes zero, a pulse is formed which opens a gate so that a counting circuit begins to count the pulses from a stable oscillator. When the input voltage becomes equal to ramp voltage, another pulse is formed which enables the closure of gate and stops the counting. Thus number of counts is proportional to the input voltage which is to be measured. So here voltage to time conversion is being carried out using ramp technique. In some instruments, the ramp voltage passes from one polarity to the opposite polarity. Two voltage comparators are used in most of the instruments of this type. One comparator produces a signal when the ramp voltage is zero. The other comparator produces a signal when the input voltage and the ramp voltage become equal.