Can you show us how you generate that -2.5~2.5 O/P from PSoC? If you get the voltage from PSoC after a capacitor, the voltage at the other end of the capacitor would be 0~5V.
What I understand from your statement is that you used an external function generator to generate a signal of amplitude -2.5V to +2.5 V. Is that correct?
It is possible to generate signal of amplitude 0-5V range using PSoC. But what kind of waveform is required? Is it sine, square or triangular?
An application note Easy Waveform generation with the WaveDAC8 Component will be of help.