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

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

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

D Flip Flop Schematic

D Flip-Flop Simulation Results CLK DIN Q QNOT

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

Voltage Reference

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

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

Resistor 50K resistor takes ~1700 um 2 We used values of 50K, 25K, 16K, and 8K Unexpectedly, resistors ended up being a small portion of our total layout

Output Buffer Unity gain opamp Open loop gain = 2560

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

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

Complete Design Schematic

Opamp 50K resistor Tx_gate (2 huge NMOS) D - Flip Flop Bias Layout

Simulation Results Complete-circuit simulation with top 7 bits active and the rest tied high (This simulation took >15 minutes to run and almost overran my storage space)

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

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 uV Just a little noisy … simulation problem or real?

Future Work / Improvements Increase resistance values to decrease tx_gate size Temperature stability (reference) Wide swing output Decrease noise on output