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Studies on CMOS Digital-to-Analog Converters
本书的部分前言 高清晰,全书约300页)
In this work we consider many of converter architectures and chips. The current-steering DAC
is pointed out as a suitable converter for both high speed and high resolution. We also investigate
the oversampling DAC (OSDAC) and discuss its properties in detail.
The performance of the converters is limited by both static and dynamic errors. The static
errors are usually caused by mismatch of the components and limit the accuracy at low speed.
The static performance is often described by measures of differential and integral nonlinearities,
(DNL and INL). For communication applications these measures are not especially used
for characterization of the DACs. Instead, the dynamic errors, such as settling errors, glitches,
etc., are more important since they increase with higher sample rates and signal frequencies.
To analyze the effect of errors it is usually easier to consider the DAC’s behavior in frequency
domain using measures, such as the spurious-free dynamic range (SFDR) and signal-to-noiseand-
distortion ratio (SFDR). These measures are normally derived from the output spectrum
when a sinusoidal input signal is used. In some applications it may be necessary to use several
sinusoidal tones to get relevant measures. Two common measures are the multi-tone power
ratio (MTPR) and the peak-to-average ratio (PAR). The PAR of the input signal affects the
maximum signal-to-noise ratio (SNR) of the converter and a small PAR is preferred since it
maximizes the SNR.
To help us understand how to design a converter several models and algorithmic expressions
are presented. The models are verified through simulations and partially through measurements
and experiments. Some of the most dominating error sources in converters, such as limited
output impedance, device mismatch, and noise, are highlighted. We give suggestions on
how to reduce and minimize the influence of these types of error sources. These techniques
involve calibration and randomization, as well as cancellation through for example pre-distortion
algorithms. We also present the basics of dynamic element matching techniques (DEM). |
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