Sigma-Delta Converter

This design example is a cost-effective, high-precision analog-to-digital converter (ADC) commonly used in wireless and audio applications, consisting of two major blocks: analog modulator and digital filter. The analog modulator over-samples and converts the analog signal into a stream of bits. The digital filter then converts the serial stream into digital number by decimation operation.

This design example shows an efficient and cost-effective way to implement the digital decimation filter with multi-stage partition method and use the time-division multiplexed (TDM) feature in DSP Builder Advanced Blockset to achieve both high-speed performance and low-resource usage.

Figure 1 shows the block diagram of a Sigma-Delta ADC with analog modulator that is modeled with a Simulink block and a digital decimation filter (implemented with a DSP Builder block).

Figure 1. Sigma-Delta ADC Block Diagram

Figure 1. Sigma-Delta ADC Block Diagram

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Tables 1 lists the specifications used to design the digital decimation filter.

Table 1. Specifications for the Digital Decimation Filter

Digital Decimation Filter Parameters


Number of Channels8
Decimation Rate Change Factor64
Input Sample Rate3.072 Mbps
Output Sample Rate (fs)48 KHz
Output Data Width16
Passband Frequency0.423 fs
Stopband Frequency0.5 fs
Passband Ripple0.04 dB
Clock Rate

24.576 MHz

Device FamilyCyclone® III


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