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
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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 Channels||8|
|Decimation Rate Change Factor||64|
|Input Sample Rate||3.072 Mbps|
|Output Sample Rate (fs)||48 KHz|
|Output Data Width||16|
|Passband Frequency||0.423 fs|
|Stopband Frequency||0.5 fs|
|Passband Ripple||0.04 dB|
|Device Family||Cyclone® III|
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