Q. Dual-ramp analog to digital converter?

Figure (a) shows the block diagram of a dual-ramp (dual-slope) A/D converter. After a start-of-conversion pulse, the counter is cleared and the analog input Vin becomes the input of the ramp generator (integrator). When the output of the ramp generator Vo reaches zero, the counter starts to count. After a fixed amount of time T, as shown in Figure (b), the output of the ramp generator is proportional to the analog input signal. At the end of T, the reference voltage Vref is selected, when the integrator gives out a ramp with a positive slope. As Vo increases, the counter is incremented until Vo reaches the comparator threshold voltage of 0 V, when the counter stops being incremented again. The value of the counter becomes the binary code for the analog voltage Vin, since the number of clock pulses passing through the control logic gate for a time t is proportional to the analog signal Vin. Dual-ramp A/D converters can provide accuracy at low cost, even though the process is slow because a double clock pulse count is an inherent part of the process