Computer Interfacing

Conversion between digital and analogue

reaches 0 V the output of the comparator will invert and

cause the control unit to disable the counter. The binary

value held by the counter is directly proportional to the

time taken for the ramp to return to zero. As the rate

which it does so is always constant it follows that the

time taken to return to zero depends upon the value of

the negative voltage from which it started. Hopefully it

is obvious that the latter in turn depends upon the value

of V

IN

the analogue input — hence the relation between

the latter and digital output.

This type of converter suffer from the same speed limi-

tation as th