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Nyquist-Rate DAC and ADC. Analog Integrated Circuit Design David Johns Ken Martin University of Toronto. Outline. The characteristic of ADC and DAC Nyquist-rate D/A converters Nyquist-rate A/D converters Conclusion. In most case, Nyquist rate converter operates
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Nyquist-Rate DAC and ADC Analog Integrated Circuit Design David Johns Ken Martin University of Toronto
Outline • 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 • DAC • Monotonic and nonmonotonic • Offset , gain error , DNL and INL • Glitch • Sampling-time uncertainty • ADC • 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) • 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) • I1 represents the MSB current • I2 represents the N-1 LSB current • ex:0111…1 to 1000…0
Sampling-Time Uncertainty • (Aperture Jitter) • Assume a full-scale sinusoidal input, • want • then
Nyquist-rate DAC • decoder-based converters • binary-weighted converters • thermometer-code converters • hybrid converters
Decoder-Based D/A converters • 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 • 4-bit folded R-string D/A converter
Decoder-Based D/A converters • Multiple R-string 6-bit D/A converter • interpolating
Decoder-Based D/A converters • 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 • Monotonicity is not guaranteed. • Potentially large glitches due to timing skews. Current-mode converter
Binary-Scaled D/A Converters • 4 bit R-2R based D/A converter • No wide-range scaling of resistors. Binary-array charge-redistribution D/A converter
Hybrid Converters Resistor-capacitor hybrid Segmented converter (thermometer-code+ binary-weighted)
Integrating converters • Low conversion rate.
Successive-Approximation Converters • Binary search
Successive-Approximation Converters • DAC-based successive-approximation converter. • 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 • High speed. Requires only one comparison cycle per conversion. • Large size and power dissipation for large N.
