Integrating
or Dual Slope ADC
•There
are basically 4 types of Analog to Digital converter (ADC).
1.Integrating
or Dual slope ADC
2.Successive
approximation ADC
3.Flash
ADC
4.Delta
sigma converter
•Dual
slope ADC is use for converting analog to digital value.
•This
is integrator.
•Dual
slope ADC is slow but have high accuracy and have high resistance to noise.
•This
method is use in digital
multimeter or digital voltmeter.
•It is
basically have integrator, comparator, control logic, clock, counter and electronically controlled
switches.
•Its
operation requires two voltage slopes hence it is name as Dual slope.
•The unknown voltage is applied to Vin and Known but with negative polarity
voltage is
applied to Vref.
•Vin
is for fixed amount of time and Vref is applied for variable amount of time.
•One slope (/) is made due to unknown voltage.
•The
negative polarity voltage is then applied until it become zero means second slope (\) will form.
•The comparator is use to detect zero crossing.
•Capacitor
charges and discharges linearly with a constant slopes.
•T
de-int is more than T int because discharging time of
capacitor is more than its charging time.
•If T de-int is large means large voltage and
if T
de-int is less means less voltage.
•When
the switch is at Vin
position capacitor charges (charging
time of capacitor is less).
•And
when the switch is at Vref position capacitor discharges (charging time of capacitor is more).
