The present work presents a new method for enhancement of contrast of coherent population trapping resonance in Rb vapour based on feedback and fast digital processing of the error signal in the feedback loop. In the proposed method, when the frequency difference between the pump field components is detuned from the resonance of coherent population trapping, a linear combination of two measured values, - pump field power prior and after passing through the cell, - is stabilised. This parameter combination is stabilised through adjustment of the pump radiation power with an electrooptical amplitude modulator. The studied method is shown to improve CPT resonance contrast by more than two orders of magnitude, while also improving the signal-to-noise ratio more than two-fold. The possibilities and limitations of the proposed method for enhancement of CPT resonance contrast are analysed.