Test: Data Converters - 2

Flash ADC is also known as parallel comparative A/D converter

1) Flash  ADC - Faster speed and low noise immunity

2) SAC  ADC - Low noise immunity and medium speed

3) RAMP  ADC - Higher resolution and good noise immunity

4) Dual Slope  ADC - Low speed and good noise immunity

For n-bit conversion, the conversion time for different ADC are:

Counter type ADC: (2ⁿ – 1) Tclk

Successive approx. time ADC: n Tclk

Flash type ADC: T_clk

Dual slope ADC: (2ⁿ+1 – 1) Tclk (Maximum time is taken)

Concept:

Flash Type ADC:

1) It is the fastest ADC among all the ADC types.

2) An n-bit flash type ADC requires:

2ⁿ -1 comparators, 2n resistors and one 2ⁿ × n priority encoder. 

Calculation:

The number of comparators required to build an 8-bit flash ADC will be:

N = 2⁸ - 1

N = 256 - 1

N = 255

Resolution: It is defined as the smallest change in the analog output voltage corresponding to a change of one bit in the digital output.

The percentage resolution (%R) of an n-bit DAC is:

The resolution of an n-bit DAC with a range of output voltage from 0 to V is given by:

Hence the difference between analog voltage represented by two adjacent digital codes of an analog to digital converter is called resolution.

Hence option (B) is the correct answer.

Concept:

For an n-bit ADC signal to noise ratio is given by

= 1.8 + 6 n dB

Where message signal → sinusoidal & noise PDF = uniform distribution

Calculation:

Given data n = 8 bit

Signal to noise ratio (SNR) = 1.8 + 6 n dB

= 1.8 + 6 x 8

= 49.8 dB

Concept:

Maximum Quantization error = 

Step size= (V_max - V_min)

Calculation:

Given

Analog voltage ranging from 0 V (V_min) to 5 V (V_max)

No. of interval or number of steps = 10

Step size = (5 - 0) = 5 V

Maximum quantization error = 1/2 × (5/10) = 0.25 V

The Digital to analog converter takes the binary number as an input and produces the analog voltage proportional to the binary number. These analog voltages represent specific analog voltage levels and have stairstep characters.

When the number of bits is not sufficient enough to represent the analog voltage levels, quantization error occurs. The greater the number of bits, the greater the number of increments over the analog range and the smaller the quantizing error.

The minimum frequency at which an analog wave should be sampled is given by Nyquist frequency. If the sampling frequency is below this limit then the analog waveform is not fully represented and leads to data loss.

ADC corresponds to Analog to Digital Converter which is used to convert an analog signal into a digital. Digital signal can be processed and manipulated.

Signal frequency = 1/ time period of the wave = 1/71.4μs = 14,006Hz.