You can find more detial introducing Decimator in the device TRM - CY8CPLC20, CY8CLED16P01, CY8C29x66, CY8C27x43, CY8C24x94, CY8C24x23, CY8C24x23A, CY8C22x13, CY8C21x34, CY8C21x34B, CY8C2…
Here is a inactive apps note which could be helpful to understand decimator - http://www.cypress.com/file/94441/download
PSoC4 does not have decimator.
... and PSoC4 does not need a separate decimator. Instead there is an averaging filter built into the ADC serving the very same functionality as the decimator in PSoC1.