Download Digital to Analog Converter for High Fidelity Audio Applications

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 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
Complete Design Schematic
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