As discussed in Part 1 of our ADC Topology Series, Analog-to-Digital converters (ADCs) are used as an interface element between the analog and digital worlds to convert an analog input into a corresponding digital output.
There is a continuing trend in the industry toward achieving higher data throughput in both wired and wireless digital communication systems. This trend results in increasingly more demanding requirements from ADCs in terms of sampling rate and conversion accuracy. Meeting these specifications requires the use of different ADC topologies. One such topology is the Sigma-Delta ADC.
Overview of Sigma-Delta ADCs
Sigma-Delta (Σ – Δ) converters are more commonly called oversampling converters or charge-balancing ADCs. A sigma-delta ADC differs from other ADC approaches by sampling the input signals at a much higher rate than the maximum input frequency. This ADC topology provides the highest resolution while still achieving high speed in the order of 24 bits at 1.5 MHz. Oversampling and noise shaping are the two key techniques employed in these ADCs. Noise shaping is the process of shaping the quantization noise of the analog-to-digital conversion by the modulation scheme, shifting it (typically) from a low bandwidth up to a higher frequency, allowing a low-pass digital filter to eliminate it from the conversion result.
Oversampling is the process of sampling a signal with a sampling frequency significantly higher than twice the bandwidth or the highest frequency of the signal being sampled. Oversampling helps avoid aliasing, improves resolution, and reduces noise. The sigma-delta ADC oversamples the desired signal by a large factor and filters the desired signal band. Unlike the Nyquist rate converters, in oversampled converters each output is obtained from a sequence of coarsely quantized input samples.
Figure 1 shows the architecture of sigma delta converters, which consist of a summing amplifier, an integrator, a comparator, and a digital filter.
Figure 1. Sigma Delta ADC Architecture
Vidatronic has several data converter IP blocks that offer flexible and efficient analog-to-digital and digital-to-analog conversion at different speeds to cover customers’ needs. Vidatronic data converters are silicon proven in several silicon processes and can be ported to any process required by our customers.
This blog post is part of a series. You can view the other posts in the series below.
(Part 5 coming soon)
To learn more about ADCs, check out our full white paper on the different ADC topologies and their applications: