In this paper, by integrating InP/InGaAsP/InP Photonic crystal semiconductor optical amplifier (PhC-SOA) with photonic crystal channel drop filters (PhC-CDF), we present a novel fully integrated ultra-small low-power all-optical analog to digital converter (AO-ADC). The self-phase modulation in the PhC-SOA can shift the frequency of the Gaussian input pulse. The two output PhC-CDFs are designed in a way that appropriately codes the frequency-shifted pulse by the PhC-SOA, which consequently converts them to four desired digital output levels. The numerical results indicated that the center wavelength of an amplitude modulated Gaussian pulse with a center wavelength of 1551.228 nm, temporal pulse-width of 10.6 ps, and energy of 74.4 fJ can be shifted by 1.652 nm. This shift is accommodated by utilizing a PhC-SOA with a length of 9 µm and an injection current of 6.5 mA. The shifted pulse is then quantized and coded to the four digital levels of (00, 01, 10, 11) by two point-defect PhC-CDFs. The PhC-CDFs minimize the AO-ADC integral and differential nonlinearity (INL/DNL) errors by compensating for the effect of the nonlinear frequency shift induced by PhC-SOA. The proposed design offers a footprint of 142 µm2 AO-ADC working at 10 Gs/s.