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Vertical topology of ELPF2 Filter
Last Updated: March 06, 2010
Question:Is it possible to have vertical topology of ELPF2 filter in PSoC devices?
Response:No.The feed forward capacitor Cpp used in the implementation of ELPF2 filter is the B input of the second stage ASD block(ASDxx)(Refer the datasheet of ELPF2 filter for the implementation details). But ASD block B inputs are limited to source blocks immediately above. For example ASD11 B input can only come from ACB00 or ACB01. To implement ELPF2 filter, the input signal should be routed to A input of ASCxx block and B input of ASDxx block in order to achieve feed forward function that provides zero in the transfer function of ELPF2 filter.
For example if the user intend to place a vertical topology ELPF2 filter in analog column 1, it is required to route the signal from ACB01(input signal) to B input of ASD11 and A input of ASC21. But the connection from ACB01 to A input of ASC21 does not exist. Similarly if the user intends to place the ELPF2 module in column 0, it is required to route the signal from ACB00(input signal) to B input of ASD20 and A input of ASC10. But the connection from ACB00 to B input of ASD20 does not exists.
This is reason for not providing vertical topology of ELPF2 filter user module in PSoC device.