Analog to Digital and Digital to Analog Converter

Analog to Digital and Digital to Analog Converter

1. Analog to Digital & Digital to Analog Converter

2. Introduction Microprocessor is a logical device which performs complex processing on digital signals. The real world physical quantities such as temperature, pressure, speed and displacement are continuous in nature. These continuous signals are analog signals. Analog signals are more susceptible to the deleterious effects of additive noise. These data converters are available as integrated circuits. DATA Converters A/D (Converts an analog signal to a digital signal) D/A (Converts a digital signal to an analog signal )

3. Digital to Analog Converter Digital to Analog (D/A) converter can be classified as: current output D/A converters voltage output D/A converters. Operational amplifier converts the current signal into a voltage signal. The performance is limited by: the number of samples it can process number of bits that is used in converting the digital code into an analog signal

4. 000 001 010 011 100 101 110 111 1/8 2/8 3/8 4/8 5/8 6/8 7/8 Digital Input Analog Output D D 1 D 2 Digital Input Analog Output D/A Converter A 3-Bit D/A Converter

5. N-bit D/A converter has n input lines, it can have 2 n input combinations. If the full scale analog voltage is 1V, the smallest unit or LSB is equivalent to 1/2 n of 1V. This is defined as resolution. The MSB represents the half of the full-scale value. For the maximum input signal, the output is equal to the value of the full scale input signal minus the value of the 1 LSB input signal.

6. Binary Weighted Input Resistors D 2 D 1 D R 1 =2K R 2 =4K R 3 =8K I 1 I 2 I 3 R f =1K I V I T I T - + V0=- R f I T Io=   V in

7. D D 1 D 2 R 1 =2K R 2 =4K R 3 =8K V ref =1V R f V - + Weighted Resistor D/A Converter

8. R f V - + D D 1 D 2 R R 2R 2R 2R 2R 1 V ref =1V R/2R Ladder Network R/2R LADDDER NETWORK

9. Analog to Digital Converter The output of transducer gives output which are in analog form, these are converted to digital signals using an ADC. An ADC is an encoding device since it is used to encode analog signals for i /p into a digital system. In many servo-controlled system & variable speed drive system use digital sensors. The feedback information from the digital sensors have to be converted into analog signals by means of DAC. Since DAC is used to decode a digital signal into an analog form, it is referred to as decoder.

10. SENSORS AND SIGNAL CONDITIONER ANALOG TO DIGITAL CONVERTER (ADC) SIGNAL CONDITIONER DIGITAL TO ANALOG CONVERTER (DAC) DIGITAL SYSTEM (COMPUTER) DIGITAL SYSTEM (COMPUTER) Analog to digital conversion Digital to analog conversion

11. Counter Type ADC Counter type ADC or Digital Ramp type The Counter type ADC is the basic type of ADC which is also called as digital ramp type ADC or staircase approximation ADC. This circuit consists of N bit counter, DAC and Op-amp comparator.

12. The N bit counter generates an n bit digital output which is applied as an input to the DAC. The analog output corresponding to the digital input from DAC is compared with the input analog voltage using an op-amp comparator. The op-amp compares the two voltages and if the generated DAC voltage is less, it generates a high pulse to the N bit counter as a clock pulse to increment the counter. The same process will be repeated until the DAC output equals to the input analog voltage.

13. If the DAC output voltage is equal to the input analog voltage, then it generates low clock pulse and it also generates a clear signal to the counter and load signal to the storage resistor to store the corresponding digital bits. These digital values are closely matched with the input analog values with small quantization error. For every sampling interval the DAC output follows a ramp fashion so that it is called as Digital ramp type ADC. This ramp looks like staircases for every sampling time so that it is also called as staircase approximation type ADC.

14. Successive Approximation ADC It includes three major elements: D/A converter, successive approximation register and the comparator. The conversion process involves comparing the output of the D/A converter V o with the analog input signal V in . The digital input to the DAC is generated using the successive-approximation method. When the DAC output matches the analog signal, the input to the DAC is the equivalent digital signal.

15. + - Comparator 4 bit D/A converter Output Register Control Successive Approximation Register D 3 D 2 D 1 D Analog Reference V in Analog Input V Status CLK Start Data Ready

16. 4-bit A/D converter Initially Bit D3 is turned on first. The output of the DAC is compared with an analog signal. If the comparator changes the state, indicating that the output generated by D3 is larger than the analog signal, bit D3 is turned off and D2 is turned on. The process continues until the input reaches bit D .