A dual-slope analog to digital converter uses an N-bit counter. When the input signal V, is being integrated, the counter is allowed to count up to the value

Concept:

In dual slope type ADC, the integrator generates two different ramps, one with the known analog input voltage V_A and another with a known reference voltage –V_ref.

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• The Dual slope ADC has many advantages as Noise present on the input voltage is reduced by averaging. 
• The value of the capacitor and conversion clock does not affect conversion accuracy, since they act equivalently on the up-slope and down-slope.
• The dual-slope ADC architecture was truly a breakthrough in ADCs for high-resolution applications such as digital voltmeters (DVMs).

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Analysis:

In dual-slope ADC, the reference voltage count up to 2^{N + 1,} and when input voltage Va is integrated, the counter is allowed to count maximum up to 2^N+1