Successive Approximation ADC

This is one of a type of Analog to Digital Converter (ADC).
Through this presentation, you will have a clear view of how an ADC works. This one specifies one of the types of Analog to Digital Convertor.

1. Abhay Dhupar (01) Abhay s. bhadoriya(02) Aditi Tomar (17) Aditya Sahu (19) Presented by :- CS - 304 DIGITAL SYSTEM Successive Approximation ADC

2. A/D CONVERTER An analog to digital(A/D) converter takes an analog input voltage and after a certain amount of time produces a digital output code which represent the analog input . This type of converter is used to convert analog voltage to its corresponding digital output. The function of the analog to digital converter is exactly opposite to that of a  DIGITAL TO ANALOG CONVERTER . Like a D/A converter, an A/D converter is also specified as 8, 10, 12 or 16 bit. Though there are many types of A/D converters, we will be discussing only about the successive approximation type.

3. APPLICATION OF (A/D)CONVERTER ADC are used virtually everywhere where an analog signal has to be processed, stored, or transported in digital form. Microphones - take your voice varying pressure waves in the air and convert them into varying electrical signals Strain Gages - determines the amount of strain (change in dimensions) when a stress is applied Thermocouple – temperature measuring device converts thermal energy to electric energy Voltmeters Digital Multimeters

4. TYPES OF A/D CONVERTER Successive approximation type A/D converter Simultaneous or Flash type A/D converter Counter type A/D converter Continuous type A/D converter Single slope type Dual slope type Voltage to Frequency (integrating) type

5. Successive approximation type A/D converter A successive approximation A/D converter consists of a comparator, a successive approximation register (SAR), output latches, and a D/A converter. The circuit diagram is shown below. A successive-approximation ADC is a type of  analog-to-digital converter  that converts a continuous  analog  waveform into a discrete  digital  representation using a  binary search  through all possible  quantization  levels before finally converging upon a digital output for each conversion.

6. Working At the start of a conversion cycle, the SAR is reset by making the start signal (S) high. The MSB of the SAR (Q7) is set as soon as the first transition from LOW to HIGH is introduced. The output is given to the D/A converter which produces an analog equivalent of the MSB and is compared with the analog input Vin. If comparator output is LOW, D/A output will be greater than Vin and the MSB will be cleared by the SAR.

7. If comparator output is HIGH, D/A output will be less than Vin and the MSB will be set to the next position (Q7 to Q6) by the SAR. According to the comparator output, the SAR will either keep or reset the Q6 bit. This process goes on until all the bits are tried. After Q0 is tried, the SAR makes the conversion complete (CC) signal HIGH to show that the parallel output lines contain valid data. The CC signal in turn enables the latch, and digital data appear at the output of the latch. As the SAR determines each bit, digital data is also available serially. As shown in the figure, the CC signal is connected to the start conversion input in order to convert the cycle continuously.

8. Advantages and disadvantages ADVANTAGES The main merit of the successive approximation type A/D converter is speed. It takes only n-clock pulses to produce n-bit resolution of the analog signal. Low power consumption. DISADVANTAGE It requires a digital to analog converter. Circuit is complex. The conversion time is more compared to flash type ADC. Limited resolution due to limits of DAC and Comparator Size increases with number of bits.

9. APPLICATION Ideal for multichannel data acquisition systems with sampling frequencies under 10 MHz and resolutions between 8-16 bits. The SAR ADC will used widely data acquisition techniques at the sampling rates higher than 10KHz