Transcript Document

Nyquist-Rate DAC and ADC
Analog Integrated Circuit Design
David Johns
Ken Martin
University of Toronto
Outline
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The characteristic of ADC and DAC
Nyquist-rate D/A converters
Nyquist-rate A/D converters
Conclusion
In most case, Nyquist rate converter operates
at 1.5 to 10 times the Nyquist rate.
The other type converter is oversampling converter
which operates at 20 to 512 times the Nyquist rate.
Characteristic of ADC and DAC
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DAC
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Monotonic and nonmonotonic
Offset , gain error , DNL and INL
Glitch
Sampling-time uncertainty
ADC
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missing code
Offset , gain error , DNL and INL
Quantization Noise
Sampling-time uncertainty
Monotonic and missing code
If DNL < - 1 LSB => missing code. (A/D)
Offset and Gain Error
D/A
A/D
D/A nonlinearity (D/A)
Differential nonlinearity (DNL): Maximum
deviation of the analog output step from the
ideal value of 1 LSB .
Integral nonlinearity (INL): Maximum
deviation of the analog output from the ideal
value.
D/A nonlinearity (A/D)
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Differential nonlinearity (DNL): Maximum
deviation in step width (width between
transitions) from the ideal value of 1 LSB
Integral nonlinearity (INL): Maximum
deviation of the step midpoints from the
ideal step midpoints. Or the maximum
deviation of the transition points from ideal.
Glitch (D/A)
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I1 represents the MSB current
I2 represents the N-1 LSB current
ex:0111…1 to 1000…0
Quantization Noise (A/D)
Sampling-Time Uncertainty
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(Aperture Jitter)
Assume a full-scale sinusoidal input,
want
then
Nyquist-rate DAC
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decoder-based converters
binary-weighted converters
thermometer-code converters
hybrid converters
Decoder-Based D/A converters
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Inherently
monotonic.
DNL depend
on local
matching of
neighboring R's.
INL depends
on global
matching of the
R-string.
Decoder-Based D/A converters
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4-bit
folded Rstring D/A
converter
Decoder-Based D/A converters
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Multiple Rstring 6bit D/A
converter
interpolati
ng
Decoder-Based D/A converters
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R-string DACs
with binary-tree
decoding.
Speed is limited
by the delay
through the
resistor string as
well as the
delay through
the switch
network.
Binary-Scaled D/A Converters
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Monotonicity is not guaranteed.
Potentially large glitches due to timing
skews.
Current-mode converter
Binary-Scaled D/A Converters
Binary-array
charge-redistribution
D/A converter
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4 bit R-2R based D/A converter
No wide-range scaling of resistors.
Thermometer-Code Converter
Hybrid Converters
Resistor-capacitor hybrid
Segmented converter
(thermometer-code+
binary-weighted)
Nyquist-Rate A/D converters
Integrating converters
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Low conversion rate.
Successive-Approximation
Converters
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Binary search
Successive-Approximation
Converters
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DAC-based successive-approximation
converter.
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Requires a high-speed DAC with precision on
the order of the converter itself.
Excellent trade-off between accuracy and
speed. Most widely used architecture for
monolithic A/D.
Flash (Parallel) Converters
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High speed.
Requires only
one
comparison
cycle per
conversion.
Large size
and power
dissipation for
large N.
Interpolating A/D Converters
Pipelined A/D Converters
Time-Interleaved ADC