Integrating ADC simulation single and dual slope using op amp

Contents:

• Introduction to Integrating ADC
• Single slope ADC
• Dual Slope ADC
• Multisim Simulation

Introduction to Integrating ADC:

Integrating analog-to-digital converters (ADCs) provide high resolution analog-to-digital conversions, with good noise rejection. These ADCs are ideal for digitizing low bandwidth signals, and are used in applications such as digital multi-meters and panel meters. They often include LCD or LED drivers and can be used stand alone without a micro controller host.

Integrating analog-to-digital converters (ADCs) provide high resolution and can provide good line frequency and noise rejection. Having started with the ubiquitous 7106, these converters have been around for quite some time. The integrating architecture provides a novel yet straightforward approach to converting a low bandwidth analog signal into its digital representation. These type of converters often include built-in drivers for LCD or LED displays and are found in many portable instrument applications, including digital panel meters and digital multi-meters.

Single-Slope ADC Architecture:

The simplest form of an integrating ADC uses a single-slope architecture. Here, an unknown input voltage is integrated and the value compared against a known reference value. The time it takes for the integrator to trip the comparator is proportional to the unknown voltage (T_INT/V_IN). In this case, the known reference voltage must be stable and accurate to guarantee the accuracy of the measurement.

One drawback to this approach is that the accuracy is also dependent on the tolerances of the integrator's R and C values. Thus in a production environment, slight differences in each component's value change the conversion result and make measurement repeatability quite difficult to attain. To overcome this sensitivity to the component values, the dual-slope integrating architecture is used.

Dual-Slope ADC Architecture:

A dual-slope ADC (DS-ADC) integrates an unknown input voltage (V_IN) for a fixed amount of time (T_INT), then "de-integrates" (T_DEINT) using a known reference voltage (V_REF) for a variable amount of time.

The key advantage of this architecture over the single-slope is that the final conversion result is insensitive to errors in the component values. That is, any error introduced by a component value during the integrate cycle will be cancelled out during the de-integrate phase. In equation form:

Vin × T_INT = V_REF × T_DEINT

or

T_DEINT = T_INT × (V_IN / V_REF)

From this equation, we see that the de-integrate time is proportional to the ratio of V_IN / V_REF.

Circuit specifications:

1. R=10k, C=0.1uF and clock frequency=1kHz.
2. Apply a DC input in range of 0V-1V 
3. Keep the clock frequency at 1kHz square-wave.

Now using these formula's calculate the values.
Here is the simulation Multisim file.Download it and modify according to your values or you can use same values.

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