In an integrating ADC, a current, proportional to the input voltage, charges a capacitor for a fixed time interval T charge.

**Dual slope
ADC (Integrating ADCs)**

In
an integrating ADC, a current, proportional to the input voltage, charges a
capacitor for a fixed time interval T charge. At the end of this interval, the
device resets its counter and applies an opposite-polarity negative reference
voltage to the integrator input. Because of this, the capacitor is discharged
by a constant current until the integrator output voltage zero again.

The
T discharge interval is proportional to the input voltage level and the
resultant final count provides the digital output, corresponding to the input
signal. This type of ADCs is extremely slow devices with low input bandwidths.
Their advantage, however, is their ability to reject high-frequency noise and
AC line noise such as 50Hz or 60Hz. This makes them useful in noisy industrial
environments and typical application is in multi-meters.

An
integrating ADC (also dual-slope or multi-slope ADC) applies the unknown input
voltage to the input of an integrator and allows the voltage to ramp for a
fixed time period (the run-up period). Then a known reference voltage of
opposite polarity is applied to the integrator and is allowed to ramp until the
integrator output returns to zero (the run-down period). The input voltage is
computed as a function of the reference voltage, the constant run-up time
period, and the measured run-down time period.

The
run-down time measurement is usually made in units of the converter's clock, so
longer integration times allow for higher resolutions. Likewise, the speed of
the converter can be improved by sacrificing resolution.

**Use: **Converters of this type (or
variations on the concept) are used in most digital** **voltmeters for their linearity and flexibility.

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Linear Integrated Circuits : Analog to Digital And Digital to Analog Converters : Dual slope ADC (Integrating ADCs) |

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