1. Digital to Analog Converter for High Fidelity Audio Applications Matt Smith Alfred Wanga CSE598A

2. Project Summary High Quality Audio Applications –Accurate Reproduction [16 bit] –Low Noise Versatile –Support for Standard Sampling Rates –Specifications that allow use in Various Audio Applications

3. R-2R Ladder Architecture * Buffer inserted on output for low output impedance

4. D Flip Flop Schematic

5. D Flip-Flop Simulation Results CLK DIN Q QNOT

6. Pass Switch NMOS pass transistor only CMOS Transmission gate not needed because we don’t go near VDD Sized to allow proper operation

7. Voltage Reference

8. Voltage Reference Results Circuit modified from Homework #3 provides 2.5V and 1.1V voltage reference Reference output stable down to ~3.3V supply voltage 2.5V reference varies by 400mV over -40C to 85C (3.2 mV/˚C) 1.1V reference varies by 150mV over -40C to 85C (1.2 mV/˚C)

9. Voltage Reference Results Power supply rejection ratio is 48dB LSB accuracy corresponds with 7mV p-p supply noise

10. Resistor 200K resistor takes ~6800 um 2 We used values of 400K, 200K, 16K, and 8K Resistors are a large part of area, but there is room to spare in the pad frame

11. Output Buffer Unity gain opamp Open loop gain = 2560

12. Output Buffer The high end wasn’t a problem – we wouldn’t go that high But what to do about the low end?

13. Output Filter This noise is partly an artifact of simulation, but a low-pass filter is a good idea anyway

14. Complete Design Schematic

15. 07 815 Opamp 200K resistors D - Flip Flops Bias Final Layout 400K resistors Transistor Switches

16. Simulation Results Complete-circuit simulation with top 7 bits active and the rest tied high

17. Simulation Results Full-circuit simulation with all 16 bits operating. LSB increments are 28uV Noise peaks are 1/4LSB

18. Design Assessment Maximum output voltage: 3.441V Minimum output voltage: 1.604V Voltage swing: 1.836V LSB voltage change: 28uV –Calculated and observed agree to +- 0.2uV Just a little noisy … simulation problem or real?

19. Future Work / Improvements Temperature stability (reference) Wide swing output Decrease noise on output