The reference level for the relative attenuation arel of TFS374B is the minimum of the pass band attenuation amin. This value is defined as the insertion loss ae. The centre frequency fc is the arithmetic mean value of the upper and lower frequencies at the 3 dB filter attenuation level relative to the insertion loss ae. The given values for the relative attenuation arel and the group delay ripple have to be reached at the frequencies given below, even if the centre frequency fc is shifted due to the temperature coefficient of frequency TCf in the operating temperature range and due to a production tolerance for the centre frequency fc.