An image sensor circuit, wherein the image sensor circuit comprises: a photo pixel array, comprising a plurality of photo pixel series, wherein a photo pixel serie comprises a plurality of photo pixel circuits, a first end of the photo pixel serie is configured to receive a clock signal, which is propagated from the first end of the photo pixel serie to a second end of the photo pixel serie, the clock signal received by each of the plurality of photo pixel circuits has a propagation delay with respect to the clock signal received by the first end of the photo pixel serie, and the photo pixel array is configured to output a plurality of pixel values; a reference pixel array, comprising at least one reference pixel serie (RPXS), wherein the reference pixel serie (RPXS) comprises a plurality of reference pixel circuits, a first end of the reference pixel serie is configured to receive the clock signal, which is propagated from the first end of the reference pixel serie to a second end of the reference pixel serie, the clock signal received by each of the plurality of reference pixel circuits has a propagation delay with respect to the clock signal received by the first end of the reference pixel serie, the each of the plurality of photo pixel circuits corresponds to one of the plurality of reference pixel circuits, the clock signal received by the each of the plurality of photo pixel circuits has a same propagation delay as the clock signal received by the corresponding one of the plurality of reference pixel circuits, the plurality of reference pixel circuits are further configured to receive reference clock signals having same phases, and the reference pixel array is configured to output a plurality of phase differences of a plurality of the clock signals received by the plurality of reference pixel circuits with respect to the reference clock signals; and an image depth determining unit, coupled to the photo pixel array and the reference pixel array, and configured to determine an image depth according to the plurality of pixel values and the plurality of phase differences. a photo pixel array, comprising a plurality of photo pixel series, wherein a photo pixel serie comprises a plurality of photo pixel circuits, a first end of the photo pixel serie is configured to receive a clock signal, which is propagated from the first end of the photo pixel serie to a second end of the photo pixel serie, the clock signal received by each of the plurality of photo pixel circuits has a propagation delay with respect to the clock signal received by the first end of the photo pixel serie, and the photo pixel array is configured to output a plurality of pixel values; a reference pixel array, comprising at least one reference pixel serie (RPXS), wherein the reference pixel serie (RPXS) comprises a plurality of reference pixel circuits, a first end of the reference pixel serie is configured to receive the clock signal, which is propagated from the first end of the reference pixel serie to a second end of the reference pixel serie, the clock signal received by each of the plurality of reference pixel circuits has a propagation delay with respect to the clock signal received by the first end of the reference pixel serie, the each of the plurality of photo pixel circuits corresponds to one of the plurality of reference pixel circuits, the clock signal received by the each of the plurality of photo pixel circuits has a same propagation delay as the clock signal received by the corresponding one of the plurality of reference pixel circuits, the plurality of reference pixel circuits are further configured to receive reference clock signals having same phases, and the reference pixel array is configured to output a plurality of phase differences of a plurality of the clock signals received by the plurality of reference pixel circuits with respect to the reference clock signals; and an image depth determining unit, coupled to the photo pixel array and the reference pixel array, and configured to determine an image depth according to the plurality of pixel values and the plurality of phase differences.