Filter cutoff tracks ADC conversion rate. (analog-digital converter)

EDN, November, 1997 by Hoskins, Kevin R.

The circuit in Figure 1 matches an antialiasing filter's cutoff frequency to an ADC's changing conversion rate. Two main design requirements are high efficiency and the ability to convert signals with varying bandwidths. To help conserve power, the circuit uses a low-power switched-capacitor filter and an ADC whose power consumption decreases as its conversion rate decreases.

The ability to change an antialiasing filter's cutoff frequency, [F.sub.C], is important when an ADC uses different conversion rates to convert analog signals. If you use a fixed-frequency filter, you'll have a tough time choosing the right cutoff frequency. For example, if you set the cutoff to handle the highest conversion rate, the cutoff may be too high when the conversion rate goes...

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