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1. Unit 5 Data Converters and PLDs 1

2. Volatile and Non Volatile Memory 2 Volatile Memory Non Volatile memory It require constant power to maintain the store information This memory can store the information even when there is no power supply to the memory or storage device It is typically use only for primary storage It is typically use only for secondary storage or long term persistent storage e.g. RAM, D-RAM, S-RAM e.g. ROM, flash memory, optical disk driver

3. Classification of Memory 3 Memory ROM RAM Masked ROM PROM EPROM EEPROM Static RAM Dynamic RAM

4. Difference between RAM and ROM 4 RAM ROM It is random access memory It is read only memory RAM is volatile ROM is non volatile It allows reading and writing It allows only reading Used in normal operation Used in start up process of computer Temporary Storage Permanent Storage It is expensive It is cheap

5. Difference between Static RAM and Dynamic RAM 5 Static RAM Dynamic RAM It contains less memory cells per unit area It contains more memory cells as compared to static RAM per unit area It has less access time hence faster memories It has greater access time than Static RAM It consists of Internal flip flop It consists of MOS transistor and capacitor Consume more power Consume less power Cost is more Cost is less It has low packing density It has high packing density It is used in cache memory It is used in main memory

6. Types of ROM 6

7. Types of DAC 7 There are two types of DAC Weighted Resistor DAC R-2R Ladder DAC

8. Weighted Resistor DAC 8

9. Weighted Resistor DAC 9 Let the 3-bit binary input is b2 b1 b0. Here, the bits b2 and b0 denote the Most significant Bit (MSB) and Least Significant Bit (LSB) respectively. The digital switches shown in the above figure will be connected to ground, when the corresponding input bits are equal to ‘0’. Similarly, the digital switches shown in the above figure will be connected to the negative reference voltage, −VR when the corresponding input bits are equal to ‘1’. In the above circuit, the non-inverting input terminal of an op-amp is connected to ground. That means zero volts is applied at the non-inverting input terminal of op-amp. According to the virtual short concept, the voltage at the inverting input terminal of opamp is same as that of the voltage present at its non-inverting input terminal. So, the voltage at the inverting input terminal’s node will be zero volts.

10. Weighted Resistor DAC 10

11. Weighted Resistor DAC 11 The above equation represents the output voltage equation of a 3-bit binary weighted resistor DAC. Since the number of bits are three in the binary (digital) input, we will get seven possible values of output voltage by varying the binary input from 000 to 111 for a fixed reference voltage, VR. Generalized output voltage equation of an N-bit binary weighted resistor DAC is The disadvantages of a weighted resistor DAC are as follows − 1. The difference between the resistance values corresponding to LSB & MSB will increase as the number of bits present in the digital input increases. 2. It is difficult to design more accurate resistors .

12. R-2R Ladder DAC 12 The R-2R Ladder DAC overcomes the disadvantages of a binary weighted resistor DAC. As the name suggests, R-2R Ladder DAC produces an analog output, which is almost equal to the digital (binary) input by using a R-2R ladder network in the inverting adder circuit. The circuit diagram of a 3-bit R-2R Ladder DAC is shown in the following figure −

13. R-2R Ladder DAC 13

14. R-2R Ladder DAC 14 Let the 3-bit binary input is b2 b1 b0. Here, the bits b2 and b0 denote the Most Significant Bit (MSB) and Least Significant Bit (LSB) respectively. The digital switches shown in the above figure will be connected to ground, when the corresponding input bits are equal to ‘0’. Similarly, the digital switches shown in above figure will be connected to the negative reference voltage, −VR when the corresponding input bits are equal to ‘1’. The advantages of a R-2R Ladder DAC are as follows − R-2R Ladder DAC contains only two values of resistor: R and 2R. So, it is easy to select and design more accurate resistors. If more number of bits are present in the digital input, then we have to include required number of R-2R sections additionally. Due to the above advantages, R-2R Ladder DAC is preferable over binary weighted resistor DAC.

15. DAC Specifications 15 Resolution : It is defined as the number of different analog output voltage levels that can be provided by a DAC. Or alternatively resolution is defined as the ratio of a change in output voltage resulting for a change of 1 LSB at the digital input. Simply, resolution is the value of LSB. Accuracy : It is the comparison of actual output voltage with expected output It is expressed in pe rcentage The accuracy of DAC should be, at worst , +- ½ of LSB Settling Time : The settling time is the time required for the DAC output to go from 0 to full scale as the binary input changes from all 0s to 1s

16. DAC Specifications 16 4. Linearity : The linearity of a D/A converter is defined as the exactness with which the digital input is converted into analog output. An ideal D/A converter produces equal increments or step sizes at output for every change in equal increments of binary input. 5. Monotonicity : A Digital to Analog converter is said to be monotonic if the analog output increases for an increase in the digital input.

17. Difference between Weighted register DAC and R-2R ladder DAC 17

18. Applications of DAC 18 Audio Amplifier - DACs are used to produce DC voltage gain with Microcontroller commands. Video Encoder - The video encoder system will process a video signal and send digital signals to a variety of DACs to produce analog video signals of various formats, along with optimizing of output levels. Display Electronics - The graphic controller will typically use a lookup table to generate data signals sent to a video DAC for analog outputs such as Red, Green, Blue (RGB) signals to drive a display. Data Acquisition Systems - Data to be measured is digitized by an Analog-to-Digital Converter (ADC) and then sent to a processor. The data acquisition will also include a process control end, in which the processor sends feedback data to a DAC for converting to analog signals. Calibration - The DAC provides dynamic calibration for gain and voltage offset for accuracy in test and measurement systems. Motor Control - Many motor controls require voltage control signals, and a DAC is ideal for this application which may be driven by a processor or controller.