CMPE 146 - [18] DAC
7. Integral Nonlinearity (INL) (a) What is integral nonlinearity? (b) What are the 2 methods of calculation? (c) What is End Point? (d) What is Best Straight Line?
(a) - It is the maximum deviation, at any point in the transfer function, of the output voltage level from its ideal value - a measure of the deviation between the ideal output and the actual measured output value for a certain input code (b) - End Point - Best Straight Line (c) End point is the deviation from the straight line through the 0 and full-scale points (d) Uses curve fitting method on the transfer function
12. DAC Design (a) What are 3 basic DAC designs?
(a) - Voltage Divider - Binary-Weighted - R/2R Ladder
4. DAC Properties (a) What are the 5 important properties of a DAC?
(a) 1. Resolution 2. Nonlinearity 3. Monotonicity 4. Settling Time 5. Update Rate
16. Advantages (a) Voltage Divider (b) Binary Weighted (c) R/2R Ladder DAC
(a) - Fast - Monotonic (b) - need to tightly control resistor ratios to maintain monotonicity (c) - few components - few resistors to trim - scalable
13. Voltage Divider (a) What is a voltage divider used for? (b) What does the voltage divider consist of? (c) What are the advantages of a voltage divider DAC? (d) What are the disadvantages of a voltage divider DAC?
(a) - used to change a large voltage to a small voltage - input code to the decoder turns on one of the switches (b) N-bit DAC consists of 2^n resistors in series and 2^n switches (c) - Fast - Monotonic (d) large number of resistors and switches for high resolution
1. DAC (a) What is a DAC? (b) Give an example of DAC.
(a) Digital to Analog Converter (b) Music File to Sound
2. Ideal DAC (a) What is an Ideal DAC? (b) What function is represented?
(a) converts the abstract numbers into a conceptual sequence of impulses that are then processed by a reconstruction filter using some form of interpolation to fill in data between the impulses (b) discrete linear transfer function
17. Disadvantages (a) Voltage Divider (b) Binary Weighted (c) R/2R Ladder DAC
(a) large number of resistors and switches for high resolution (b) - need to tightly control resistor ratios to maintain monotonicity - hard to achieve high resolution due to variations of resistors (c) - few components - few resistors to trim - scalable
14. Binary-Weighted DAC (a) What is a binary-weighted DAC? (b) What does the binary-weighted DAC? (c) What is the output current Iout? (d) What are the advantages of a binary-weighted DAC?
(a) produces an analog output by using binary weighted resistors and outputs the sum of individual current called current Iout (b) N-bit DAC consists N binary-weighted resistors, N switches (c) output current Iout is the sum of individual currents through the resistors (d) few components (e) - need to tightly control resistor ratios to maintain monotonicity - hard to achieve high resolution due to variations of resistors
3. Support Circuits (a) What does the voltage reference provide for a DAC? (b) What does a filter do in a DAC? (c) What kinds of filter is passed? (d) What are the advantages of using a filter?
(a) provides DAC a precise reference voltage to produce the correct output voltages (b) - A DAC produces a constant voltage level (step function) periodically - Filter smooths out the ragged edges of the piece wise output signal (c) Essentially a low-pass filter to produce a smooth analog output signal (d) - Interpolates the signal between 2 successive output voltage levels - Removes high frequency components
15. R/2R Ladder DAC (a) What is a R/2R Ladder DAC? (b) What does a R/2R Ladder consist of? (c) What are the advantages of a R/2R Ladder DAC?
(a) simple and inexpensive way to perform DAC using repetitive arrangements of precise resistor networks in a ladder like configuration (b) 2N resistors of only two values in the ratio of 1:2, N switches (c) - few components - few resistors to trim - scalable (d) higher noise on large current swing
9. Monotonicity (a) How does a monotonic DAC behave? (b) When will it be non-monotonic?
(a) the analog output always increases or remains constant as the digital input increases (b) if the analog output decreases at any point during the input sequence
6. Nonlinearity (a) What is nonlinearity? (b) What is it typically expressed in? (b) What are the 2 types of nonlinearity?
(a) the error between the desired analog output and the actual output (b) typically expressed in terms of numbers of LSB's (c) - Differential - Integral
10. Settling Time (a) What is settling time? (b) What does the settling time determine?
(a) the interval between the output voltage starts to change and it settles within the Vlsb of the expected value (b) determines the maximum output update rate
8. Differential Nonlinearity (DNL) (a) What is differential nonlinearity?
(a) the maximum deviation of an actual analog output step, between adjacent input codes, from the ideal step value - the deviation between 2 analog values corresponding to adjacent input digital values
11. Update Rate (a) What is the definition of update rate in a DAC? (b) What does the update rate depend on?
(a) the maximum speed at which the DAC circuitry can operate and still produce correct output (b) - depends on the clock speed of the input signal - depends on the settling time of converter
5. Resolution (a) What is the resolution of a DAC? (b) What is the amount of variance? (c) What does it measure? (d) What are the benefits of having a higher resolution?
(a) the number of bits representing the digital values (b) amount of variance in output voltage for every change of the LSB in the digital input (c) a measure of how closely we can approximate the desired output signal (d) higher resolution = smaller voltage division = finer detail on output
