12-bit digital-analog converterjmorizio/ee299/projects_2010/12bitdac.pdf · design of a 12-bit...
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12-bit Digital-Analog Converter
ECE262 Analog Circuit Design
Team MemberTeam MemberTeam MemberTeam Member
Chao ChenChao ChenChao ChenChao ChenJae Jae Jae Jae ShikShikShikShik LimLimLimLim LingzhaoLingzhaoLingzhaoLingzhao XieXieXieXie
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Agenda
Abstract
Background
Block Diagram
Module Level Design
System Level Design
Design Review
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Abstract
Design of a 12-bit Digital-Analog Converter with mixed-signal design
The lower 8 bits of digital-analog conversion are implemented by R-2R Ladder while the upper 4 bits are implemented by Binary-to-Thermometer Decoder
Carefully design the Op-Amp to optimize the performance of the DAC
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BackgroundBinary-to-Thermometer Decoder
R-2R ladder requires significantly high precision
resistors and is usually limited to a max of 8-bit
resolution.
The implementation of Thermometer Decoderallows for a 12-bit resolution while only needing
the accuracy of a 8-bit DAC
N inputs thermometer decoder has 2n−1 outputs.
Each output corresponds to a base 10 value of the
possible binary inputs.
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Background Example of 3bits Binary-to-Thermometer Decoder
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Three bits input and corresponding seven outputs
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Background R-2R Ladder with Thermometer Decoder
R Array
R-2R Ladder
4 bits
Thermometer
Decoder
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OpampAnalogoutputAnalog
Low Pass Filter
Thermometer
Decoder
4-bit
+R-2R
Ladder
15-bit
LSB
MSB
R Array
8-bit
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Block Diagram
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Module Design
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R-2R Ladder and R Array Module
Opamp
Low Pass Filter
Thermometer
Decoder
R-2R Ladder
R Array
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R-2R Ladder (8bits)
Schematic
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R-2R Ladder (8bits)
Simulation using Hspice (Inputs)
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R-2R Ladder (8bits)
Simulation using Hspice (Output)
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R-2R Ladder and R Array Module
Layout (Both LVS and DRC clean)
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4bits Thermometer Decoder Module
Opamp
Low Pass Filter
Thermometer
Decoder
R-2R Ladder
R Array
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15 bits output to R Array 15
4bits Thermometer Decoder Module Schematic
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R Array
R-2R Ladder
Thermometer
Decoder
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4bits Thermometer Decoder Module Schematic
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4bits Thermometer Decoder Module Simulation using Eldo (12bits input)
Inputs for the thermometer decoder and R-2R array
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4bits Thermometer Decoder Module Simulation using Eldo (output)
Output of the thermometer decoder and R-2R array
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3.29422
3.29290
Resolution=1.3mV
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4bits Thermometer Decoder Module Simulation using Eldo (magnified output)
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4 input NAND 3 input NAND4 input NOR 3 input NOR
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4bits Thermometer Decoder Module Layout for MOS Gates
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2 input NAND 2 input NOR
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4bits Thermometer Decoder Module
Layout for MOS Gates
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4bits Thermometer Decoder Module
Layout (Both DRC and LVS Clean)
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OP Amplifier Module
Opamp
Low Pass Filter
Thermometer
Decoder
R-2R Ladder
R Array
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OP Amplifier Module
Schematic
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Linear through the whole range Input range: 0.575V ~ 4.807V DC Gain: 72.775 dB Phase Margin: 81.865 degrees Unity Gain Bandwidth: 28 MHz Slew rate: 8.4V/us
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OP Amplifier Module
Specification
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R, R-2R
Output
OPAMP
Output
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OP Amplifier Module
Simulation using Eldo
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1.3mV
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OP Amplifier Module
Simulation using Eldo
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OP Amplifier Module
Layout (Both DRC and LVS Clean)
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OP Amplifier Module
Layout (General View)
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Tail bias Out bias30
OP Amplifier Module
Layout (Details)
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P Load P Out
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OP Amplifier Module
Layout (Details)
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Common
Centroid
Differential
Pair
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OP Amplifier Module
Layout (Details)
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Low Pass Filter Module
Opamp
Low Pass Filter
Thermometer
Decoder
R-2R Ladder
R Array
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Active Low Pass Filter
Schematic
Second-order unity-gain Tschebyscheff LPF
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Active Low Pass Filter
Simulation - Hspice
Cut off frequency: 27.24MHz
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Active Low Pass Filter
Simulation - Hspice
Roll-off of 2nd order LPF: 39.6712 dB/decade
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Active Low Pass Filter
Layout OPAmp
5k Ω
2ea
22pF
0.3pF
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System Design
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12-bit Digital-Analog Converter Top Level Schematic
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Thermometer
Decoder +
R Array
Dummy
R and C
Source Follower
ActiveFilter
Analog
VDD
Analog
GND
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R, R-2R
Output
OPAMP
Output
LPF
Output
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12-bit Digital-Analog Converter Top level simulation using Eldo
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12-bit Digital-Analog Converter Layout (Both DRC and LVS Clean)
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12-bit Digital-Analog Converter All module layout
Thermometer
Decoder
(Digital)
R Array
(Analog)
OP Amp &
LPF
(Analog)
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12-bit Digital-Analog Converter Layout – Guard Rings
Digital Logic
Analog Circuit
P+
(GND)
N well, N+
(GND)
P+
(A Gnd)
N well, N+
(A Vdd)
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12-bit Digital-Analog Converter Simulation using Eldo (Max. at 14MHz)
Stable state exist, operate well at 14MHz
OPAMP
Output
R, R-2R
Output
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Input bits: 12-bit
Input voltage: 5V
Output range: 0.58V ~ 4.80V
Resolution: 1.3mV
Bandwidth: 14MHz
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Design ReviewSpecification
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R and R-2R Array9 resistors with resistance 2R (=2*20 kΩ)22 resistors with resistance R (=20 kΩ)
Thermometer Decoder2 Input NAND: 8 ea 3 Input NAND: 3 ea 4 Input NAND: 1 ea2 Input NOR: 8 ea 3 Input NOR: 3 ea 4 Input NOR: 1 eaInverter: 15 ea
OP-AMPNmos: 5, Pmos: 4, C: 5pF*1
2nd order Low Pass Filter
OP-AMP Capacitor: 0.3 pF, 22pF Resistor: 5 kΩ * 2
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Design ReviewComponent used
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Total power consumption (from Eldo)
P_system=1.5647mW
Total Area: 1.4453 mm2
1077um * 1342 um = 1.4453 mm2
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Design ReviewPower consumption & Area used
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In order to improve the non linearity of analog output, we have calibrated the resistor values connected to output of the thermometer decoder
The waveform on the next slide shows that the output of resistor array has almost linear output
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Design ReviewOutput calibration
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Design ReviewOutput calibration – simulation (Eldo)