The decimation filter is the function in the ??? converter, before the serial interface ( Figure 13-20). The primary job of the decimation filter is to slow the data output rate and provide further signal bandlimiting. This seems like it would not be a good idea, but in fact, the converter user is not interested in the intermediary averaging steps that the converter implements. Instead, the user is only interested in the final results. So with this filter, the output data rate speed is reduced considerably with respect to the sampling frequency. The digital filter and decimation filter both reside in the same silicon space.

Figure 13-20: The purpose of a decimation filter is to slow the output data rate to match the output data rate to the input frequency bandwidth. The FIR lowpass filter inputs a multibit data stream to the input of the decimation filter. The simplest decimation filter filters out several conversion results while keeping enough to meet the output data rate of the converter

The discrete, high-precision analog front end in the data acquisition circuit is not outdated but is being gently pushed further into its exclusive corner. This is not to say that the demand for precision data acquisition circuits has disappeared. The solutions to these problems are changing in orientation from the analog-dominated circuit to digital. Although the task of signal processing seems to be migrating to the digital domain, good analog engineering practices still apply. To my delight, it...