Cirrus-logic AN241 User Manual download pdf (Page 14)

AN241

Figure 7. Single Ended Input Buffer with a Common Reference Pin

5.4 Overview of Filter Topology

5.4.1 High Pass Filter and DC Biasing

The first stage of the buffer forms a high pass filter from the combination of the AC-coupling capacitor

along with the resistor divider that biases the positive terminal of the op-amps to the proper DC bias volt-

age. The value of the resistors denoted as “R” will vary depending on the optimal DC bias for the given

converter. Typically this is around half of the VA voltage supply. Please refer to the converter datasheet

for the recommended input bias voltage. The 3dB corner of the high pass filter can be calculated as fol-

lows:

where:

is the value of the resistor divider in parallel (in Ohms)

is the value of the AC-coupling capacitor (in Farads)

Ω

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Cirrus-logic AN241 User Manual Page 14