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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
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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 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 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 um2 • 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
Layout Bias 0 7 15 8 Opamp Tx_gate (2 huge NMOS) 50K resistor D - Flip Flop
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 +- 0.2uV • 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