Single Supply Active Filter with Virtual Ground


Posted on Feb 7, 2014

All filter stages using a Virtual Ground will have the Virtual Ground DC potential on their outputs, while all stages having a resistive divider on their input (and no virtual Ground) will have the divider potential on their output. For supply currents of up to 20 ma, the TLE2426 (and the TLE2425 for 5V circuits) provide a low cost and space effective precision virtual ground.


Single Supply Active Filter with Virtual Ground
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Output impedance is typically less than 1 ohm for frequencies up to 30kHz ( when sourcing or sinking 10 ma). The 8-pin version has an additional Noise Reduction pin, allowing an external capacitor to bypass the internal divider junction (a 1uF capacitor could be used). It is possible to add capacitors between the output Vgnd and the two rails, in order to provide higher instantaneous source and sink currents, as long as the average current doesn`t exceed the TLE2426 output current capacity. Note that any such capacitors will add poles that could interfere with the active filter circuit response. This circuit can be used as an alternative to the TLE2426, or whenever the required Virtual Ground current exceeds 20ma. For small currents (~5ma), a general purpose op amp can be used, such as the TL071 or uA741. For very high currents, the following op amps could be considered: Note that as with all filter op amps, both rails should be bypassed with 0. 1uF and 1uF capacitors. Star grounding of all true grounds (Virtual Ground excluded) is recommended. Several micropower voltage regulators provide an adjustable voltage output and at least 40ma output current, with very low quiescent current. Probably the most common is the ADM663 (also MAX663), which can be configured with only 2 external resistors, and an optional third resistor for current limiting (Rcl). If current limiting is not required, then SENSE should be connected to...




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