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)

D/A Offset and Gain Error 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

Quantization Noise (A/D)

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 interpolati ng

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 Binary-array charge-redistribution D/A converter  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  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.

Interpolating A/D Converters

Pipelined A/D Converters

Time-Interleaved ADC