what are the main advantages and disadvantes of sigma delta ADCs compared to other ADC architectures.
Most of the circuitry in sigma delta converters is digital, allowing these converters to be fabricated on a wide range of IC processes. This implies that performance will not drift significantly with time and temperature. They are inherently monotonic (i.e., a change in the digital output has always the same slope as the analog input). This is of particular importance in closed-loop control systems, where misinterpretation of the direction of change of a measured variable may cause the system to become unstable. They are inherently linear, and present little differential non-linearity. External sample & hold circuits are not required due to the high input sampling rate and low precision of the A to D conversion in the modulator, (the devices are inherently self-sampling and tracking). Requirements for analog anti-aliasing filters are minimum - in most cases, a simple single pole RC-filter suffices as the bandwidth of interest is considerably lower than the first image that occurs about the modulator frequency. In contrast, the filters required for medium- to high-resolution applications using other (non-oversampling) technologies are very sophisticated, difficult to design, large, and expensive.
The penalty paid for the high resolution achievable with sigma delta technology has always been speed: the hardware has to operate at the over-sampled rate, much larger than the maximum signal bandwidth, thus demanding great complexity of the digital circuitry. Because of this limitation, sigma delta converters have traditionally been relegated to high-resolution, very-low frequency applications and more recently speech, audio and medium speeds (100 kHz to 1 MHz).
The digital filtering stage results in long latency between the start of the sampling cycle, and the first valid digital output; similarly, there is a significant lag thereafter between digital outputs and their corresponding sampling instants. These characteristics reduce the throughput time in multiplexed systems as it takes many clock cycles for the digital filter to settle after switching from one channel to the next.
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