A wide variety of conversion methods are usedin A/D converters. A/D converters in slope technology are relatively simple in design and operate with a relatively low sampling rate. In addition to the slope method, which works with a sawtooth, there is also the counting method and the dual-slope method, which is based on charge and discharge functions.
The slope method is a comparison method in which the input voltage to be digitized is compared with a defined sawtooth voltage. If the voltage is equal, the magnitude for the input voltage is digitally derived from the defined time of the sawtooth.
A slope converter consists of a comparator to whose one input the input voltage and to whose second input a defined sawtooth is applied, which is generated in a sawtooth generator. The output of the comparator is connected to a counter, which in turn is connected to a quartz oscillator.
The sawtooth voltage is triggered by a start pulse, which simultaneously enables the counter. The sawtooth voltage increases continuously from below 0 V until it corresponds to the input voltage. During the sawtooth rise, i.e. from the voltage value 0 V, a gate voltage operates, which enables the counter. This then counts the pulses transmitted by the crystal oscillator. As soon as the sawtooth voltage has reached the voltage value of the input voltage, the counting process is stopped by the gate voltage. The number of pulses counted is proportional to the voltage level of the input voltage. After resetting the counter, a new counting process can be initiated.
The dual-slope method, which uses two sawtooth-shaped charge functions and integration elements, is different. With this method, the discharge time serves as the decisive factor for the input voltage.