The invention provides a multi-coil unit including first, second, . . . , (n−1)-th, and n-th coil elements corresponding to a number n of quantization bits of a digital signal, the coil elements including coil wires of a same length. The multi-coil unit has a winding structure in which the coil wires are wound a plurality of times to be stacked in a magnetic flux direction to form a plurality of tires.